Co-reporter:Liangliang Zhang, Zhendong Hao, Xia Zhang, Guo-Hui Pan, Yongshi Luo, Huajun Wu, Xuewei Ba, and Jiahua Zhang
Inorganic Chemistry November 6, 2017 Volume 56(Issue 21) pp:13062-13062
Publication Date(Web):October 9, 2017
DOI:10.1021/acs.inorgchem.7b01794
Er3+-induced intensity enhancement of ∼2 μm emission is observed in 2 atom % Tm3+ doped Lu2O3 under 782 nm excitation. The maximum enhancement reaches 41.9% with only 0.05 atom % Er3+. Er3+ introduces a new quantum cutting process which is proved to be a Tm3+ → Er3+ → Tm3+ forward–backward energy transfer (FBET) system. The FBET system is observed to work efficiently even at very low Er3+ concentration. Thus, energy loss due to energy migration among Tm3+ ions is suggested to be suppressed by the FBET process. The Tm3+ → Er3+ → Tm3+ FBET system may be a new route to improve the performance of Tm3+ lasers.
Co-reporter:Guotao Xiang, Yan Ma, Wen Liu, Jiapeng Wang, Zhiwei Gu, Ye Jin, Sha Jiang, Xiaobing Luo, Li Li, Xianju Zhou, Yongshi Luo, and Jiahua Zhang
Inorganic Chemistry November 20, 2017 Volume 56(Issue 22) pp:13955-13955
Publication Date(Web):November 2, 2017
DOI:10.1021/acs.inorgchem.7b02086
The red upconversion (UC) emission of Eu3+ ions in Lu2O3: Yb3+/Eu3+ powders was successfully enhanced by tridoping Ho3+ ions in the matrix, which is due to the bridging function of Ho3+ ions. The experiment data manifest that, in Yb3+/Eu3+/Ho3+ tridoped system, the Ho3+ ions are first populated to the green emitting level 5F4/5S2 through the energy transfer (ET) processes from the excited Yb3+ ions. Subsequently, the Ho3+ ions at 5F4/5S2 level can transfer their energy to the Eu3+ ions at the ground state, resulting in the population of Eu3+ 5D0 level. With the assistance of the bridging function of Ho3+ ion, this ET process is more efficient than the cooperative sensitization process between Yb3+ ion and Eu3+ ion. Compared with Lu2O3: 5 mol % Yb3+/1 mol % Eu3+, the UC intensity of Eu3+ 5D0→7F2 transition in Lu2O3: 5 mol % Yb3+/1 mol % Eu3+/0.5 mol % Ho3+ is increased by a factor of 8.
Co-reporter:Guotao Xiang, Yan Ma, Wen Liu, Sha Jiang, Xiaobing Luo, Li Li, Xianju Zhou, Zhiwei Gu, Jiapeng Wang, Yongshi Luo, and Jiahua Zhang
Inorganic Chemistry August 7, 2017 Volume 56(Issue 15) pp:9194-9194
Publication Date(Web):July 12, 2017
DOI:10.1021/acs.inorgchem.7b01236
The monochromaticity improvement of green upconversion (UC) in Lu2O3:Yb3+/Ho3+ powders has been successfully realized by tridoping Eu3+. The integral area ratio of green emission to red emission of Ho3+ increases 4.3 times with increasing Eu3+ doping concentration from 0 to 20 mol %. The energy transfer (ET) mechanism in the Yb3+/Ho3+/Eu3+ tridoping system has been investigated carefully by visible and near-infrared (NIR) emission spectra along with the decay curves, revealing the existence of ET from the Ho3+ 5F4/5S2 level tothe Eu3+ 5D0 level and ET from the Ho3+ 5I6 level to the Eu3+ 7F6 level. In addition, the population routes of the red-emitting Ho3+ 5F5 level in the Yb3+/Ho3+ codoped system under 980 nm wavelength excitation have also been explored. The ET process from the Yb3+ 2F5/2 level to the Ho3+ 5I7 level and the cross-relaxation process between two nearby Ho3+ ions in the 5F4/5S2 level and 5I7 level, respectively, have been demonstrated to be the dominant approaches for populating the Ho3+ 5F5 level. The multiphonon relaxation process originating from the Ho3+ 5F4/5S2 level is useless to populate the Ho3+ 5F5 level. As the energy level gap between the Ho3+ 5I7 level and Ho3+ 5I8 level matches well with that between Eu3+ 7F6 level and Eu3+ 7F0 level, the energy of the Ho3+ 5I7 level can be easily transferred to the Eu3+ 7F6 level by an approximate resonant ET process, resulting in a serious decrease in the red UC emission intensity. Since this ET process is more efficient than the ET from the Ho3+ 5F4/5S2 level to the Eu3+ 5D0 level as well as the ET from the Ho3+ 5I6 level to the Eu3+ 7F6 level, the integral area ratio of green emission to red emission of Ho3+ has been improved significantly.
Co-reporter:Wenge Xiao, Dan Wu, Liangliang Zhang, Xia Zhang, Zhendong Hao, Guo-Hui Pan, Ligong Zhang, Xuewei Ba, and Jiahua Zhang
Inorganic Chemistry August 21, 2017 Volume 56(Issue 16) pp:9938-9938
Publication Date(Web):August 10, 2017
DOI:10.1021/acs.inorgchem.7b01457
Forming solid solutions through cation substitution is an efficient way to improve the luminescence properties of Ce3+ or Eu2+ activated phosphors and even to develop new ones, which is badly needed for phosphor-converted white LEDs. Here, we report new color tunable solid solution phosphors based on Eu2+ activated K2Al2B2O7 as a typical case to demonstrate that, besides crystal field splitting of 5d levels, centroid shift and Stokes shift can be dominant in tuning excitation and emission spectra as well as thermal stability of solid solution phosphors, both of which were previously considered to be negligible. Moreover, a general model involving the inductive effect of neighboring cations is proposed to explain the obvious variations in centroid shift and Stokes shift with cation substitution. Our work is propitious for the construction of more reasonable structure–property relations and thus offers theoretical guidance for designing solid solution phosphors.
Co-reporter:Wen Liu;Zhendong Hao
Journal of Materials Science: Materials in Electronics 2017 Volume 28( Issue 11) pp:8017-8022
Publication Date(Web):20 March 2017
DOI:10.1007/s10854-017-6506-5
Near-infrared downconversion phenomenon has been demonstrated in Lu2O3: Tm3+/Yb3+ phosphor upon direct excitation of Tm3+:1G4 level at 463 nm. The efficient energy transfer from Tm3+: 1G4 → Yb: 2F5/2 has been elucidated by the excitation spectra, the visible and NIR spectra as well as the decay curves of Tm: 1G4 state. The mechanism of downconversion in Lu2O3:Tm3+/Yb3+ has been discussed in detail. According to analysis of the dependence of the initial transfer rate over Yb3+ ion concentration, it could be included that energy transfer (ET) from Tm3+ to Yb3+ is a single-step ET process instead of a cooperative one. By varying the Yb3+ concentrations, we obtain the Lu2O3: 0.2%Tm3+/30%Yb3+ sample with theoretical quantum efficiency as high as 148.2%. Because the excited state of Yb3+ just above the band edge of crystalline silicon, it suggested that Lu2O3: Tm3+/Yb3+ sample will be beneficial to improve the conversion efficiency of c-Si solar cells.
Co-reporter:Anqi Zhang, Zhen Sun, Guofeng Liu, Zuoling Fu, Zhendong Hao, Jiahua Zhang, Yanling Wei
Journal of Alloys and Compounds 2017 Volume 728(Volume 728) pp:
Publication Date(Web):25 December 2017
DOI:10.1016/j.jallcom.2017.09.010
•Er3+/Tm3+/Ho3+ doped NaYb(MoO4)2 phosphors show strong visible luminescence.•FIR technique of thermally coupled states (TCS) and non-TCS have been explained.•The temperature sensor has high sensitivity in wide range (323–573 K).Well-crystallized NaYb(MoO4)2 doped with lanthanide ions (Ln3+: Er3+, Tm3+ and Ho3+) are successfully synthesized by hydrothermal method with further calcination. And the samples with different morphologies are obtained by changing the pH values and the molar ratio of Ln(NO3)3/Na2MoO4 of the resultant solutions. The upconversion (UC) luminescence spectra of NaYb(MoO4)2: Ln3+ between 323 K and 573 K under 980 nm excitation exhibit temperature-dependent property. The fluorescence intensity ratio (FIR) techniques with thermally coupled states (TCS) (Er3+: 2H11/2, 4S3/2 → 4I15/2, Tm3+: 1G4(1),(2) → 3H6, Ho3+: 5F5(1),(2) → 5I8) have high sensitivity (S) values (Er3+: 0.0122 K−1 at 548 K, Tm3+: 0.0025 K−1 at 323 K and Ho3+: 0.00035 K−1 at 323 K). The non-TCS (Ho3+: 5F5, 5S2/5F4 → 5I8) is used to extend the range of S, and the slope of FIR (non-TCS)-T is the S value as high as 0.02455 K-1 in the wide temperature range from 323 K to 573 K.Download high-res image (247KB)Download full-size image
Co-reporter:Dan Wu, Wenge Xiao, Xia Zhang, Zhendong Hao, Guo-Hui Pan, Liangliang Zhang, Yongshi Luo, Jiahua Zhang
Journal of Alloys and Compounds 2017 Volume 722(Volume 722) pp:
Publication Date(Web):25 October 2017
DOI:10.1016/j.jallcom.2017.06.088
•2 μm emission of Tm3+:3F4 → 3H6 transition is largely enhanced by codoping Yb3+.•The BET efficiency is as high as 88% for codoping with 10 mol% Yb3+.•The BET upon 782 nm excitation is more efficient than ET upon 980 nm excitation.Tm3+ doped luminescence materials have attracted great attention owing to their potential for achieving 2 μm laser. Here, we report that the 2 μm emission intensity of Tm3+:3F4 → 3H6 transition can be enhanced by as large as 1.8 times through introducing Yb3+ into Tm3+ doped Y2O3 upon 782 nm excitation, where the population of Tm3+:3F4 level is increased by backward energy transfer from Yb3+ following the forward energy transfer from the upper level Tm3+:3H4 to an intermediate level Yb3+:2F5/2. In addition, the efficiencies of Yb3+ to Tm3+ backward energy transfer are determined based on the analysis of emission spectra and fluorescence time profiles. It is found that the Yb3+ to Tm3+ backward energy transfer upon Tm3+ excitation at 782 nm is more efficient than the Yb3+ to Tm3+ energy transfer upon Yb3+ direct excitation at 980 nm, which is explained by the preferential excitation of Yb3+ with a nearby Tm3+ in the forward energy transfer from Tm3+ to Yb3+ upon Tm3+ excitation. Our results demonstrate that codoping Yb3+ into Tm3+ activated materials offers a promising approach to obtain efficient 2 μm laser, and the efficient backward energy transfer may play a key role in other rare earth ions doped luminescence materials.
Co-reporter:Dan Wu;Wenge Xiao;Liangliang Zhang;Xia Zhang;Zhendong Hao;Guo-Hui Pan;Yongshi Luo
Journal of Materials Chemistry C 2017 vol. 5(Issue 45) pp:11910-11919
Publication Date(Web):2017/11/23
DOI:10.1039/C7TC03941G
Developing phosphors with high quantum efficiency and superior thermal stability is still a challenge for phosphor-converted white light-emitting diodes (w-LEDs). Energy transfer between ions is usually utilized to tune the emission wavelength. In this study, we demonstrate that in addition to the tunable emission color, an improved thermal stability can be achieved by energy transfer from Ce3+ to Tb3+ in Ce3+ and Tb3+ codoped Ba2Y3(SiO4)3F (BYSF:Ce3+,Tb3+) phosphors without quantum efficiency loss, which is ascribed to the combined effect of fast energy transfer within the nearest Ce3+–Tb3+ pairs via electric dipole–quadrupole interactions, and the following energy diffusion among the Tb3+ ions. An efficient energy transfer from Ce3+ to Tb3+ results in the novel green phosphor BYSF:2%Ce3+,40%Tb3+ with an internal quantum efficiency of as high as 83.12%. In addition, a w-LED lamp was fabricated to explore its possible application in w-LEDs based on near UV LEDs. Our results indicate that fast energy transfer to Tb3+ may provide an alternative way of improving the thermal stability of phosphors.
Co-reporter:Guotao XiangYan Ma, Xianju Zhou, Sha Jiang, Li Li, Xiaobing Luo, Zhendong Hao, Xia Zhang, Guo-Hui Pan, Yongshi Luo, Jiahua Zhang
Inorganic Chemistry 2017 Volume 56(Issue 3) pp:
Publication Date(Web):January 18, 2017
DOI:10.1021/acs.inorgchem.6b02600
A high-temperature solid-state method was used to synthesize the Ho3+- and Yb3+-codoped cubic Lu2O3 powders. The crystal structures of the as-prepared powders were characterized by X-ray diffraction. The energy-transfer (ET) phenomenon between Ho3+ ions and Yb3+ ions was verified by the steady-state spectra including visible and near-infrared (NIR) regions. Beyond that, the decay curves were also measured to certify the existence of the ET process. The downconversion phenomena appeared when the samples were excited by 446 nm wavelength corresponding to the transition of Ho3+: 5I8→5G6/5F1. On the basis of the analysis of the relationship between the initial transfer rate of Ho3+: 5F3 level and the Yb3+ doping concentration, it indicates that the ET from 5F3 state of Ho3+ ions to 2F5/2 state of Yb3+ ions is mainly through a two-step ET process, not the long-accepted cooperative ET process. In addition, a 62% ET efficiency can be achieved in Lu2O3: 1% Ho3+/30% Yb3+. Unlike the common situations in which the NIR photons are all emitted by the acceptors Yb3+, the sensitizers Ho3+ also make contributions to the NIR emission upon 446 nm wavelength excitation. Meanwhile, the 5I5→5I8 transition and 5F4/5S2→5I6 transition of Ho3+ as well as the 2F5/2→2F7/2 transition of Yb3+ match well with the optimal spectral response of crystalline silicon solar cells. The current research indicates that Lu2O3: Ho3+/Yb3+ is a promising material to improve conversion efficiency of crystalline silicon solar cell.
Co-reporter:Wenge XiaoDan Wu, Liangliang Zhang, Xia Zhang, Zhendong Hao, Guo-Hui Pan, Haifeng Zhao, Ligong Zhang, Jiahua Zhang
The Journal of Physical Chemistry C 2017 Volume 121(Issue 5) pp:
Publication Date(Web):January 13, 2017
DOI:10.1021/acs.jpcc.6b11633
As is well-known, the aliovalent substitution level is usually very limited due to the charge mismatch. Particularly, the single phase can hardly be obtained by solid-state reaction for the famous silicate garnet Ca3Sc2Si3O12 (CSS), even when the doping level of trivalent rare earth ion (RE3+) for Ca2+ in CSS is lower than 2 mol %, which largely restricts CSS to be an ideal host for RE3+-activated luminescence materials especially where high doping concentration is required. Herein, by using the strategy of multiple chemical unit cosubstitution, we obtained RE3+ heavily doped single-phase CSS via the sol–gel method followed by high-temperature sintering. Multiple chemical unit substitutions of [REO8], [AlO6], and [AlO4], respectively, for [CaO8], [ScO6], and [SiO4] polyhedra can act as charge compensators for each other to promote the doping level of RE3+ up to 20 mol %, which is high enough for most of the RE3+-doped luminescence materials. Moreover, intense cooperative upconversion (UC) luminescence (UCL) was observed in Yb3+ and Tb3+ codoped CSS, whose intensity is 37 times higher than that of the reported Y3Al5O12 with garnet structure as well, making it a potential candidate for optical applications like a tunable UC laser. The results show that the preferred formation of the Yb3+–Yb3+ pair in CSS can largely enhance the efficiency of the cooperative UC process. Besides, the UCL properties were investigated in detail to understand the UC processes and the underlying energy transfer mechanisms. It is confirmed that the multiple chemical unit cosubstitution is an effective strategy to promote the aliovalent substitution level or design solid solution materials to enhance or tune the luminescence properties where relatively high doping concentration is required.
Co-reporter:Zhendong Hao, Ying Wang, Liangliang Zhang, Guohui Pan, Xia Zhang, Huajun Wu, Yongshi Luo, Jiahua Zhang
Optical Materials 2017 Volume 71(Volume 71) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.optmat.2017.03.051
•The addition of NH4Cl produced the emission of Eu2+ in CaO.•Efficient blue emission of Eu2+ can be excited under 400 nm near ultraviolet light.•High thermal stability with 94% of luminescent intensity remains at 120 °C.In this paper, we synthesized series of Eu2+ activated CaO ceramic powders by conventional solid state reaction. Using NH4Cl as a reducing additives, the Eu3+ has been successfully reduced to Eu2+. An intense blue emission peaked at 460 nm from Eu2+ was observed. The luminescent intensity of the doping-optimized CaO:Eu2+ sample can be as high as 106% of commercial BAM blue phosphor under 400 nm near-ultraviolet (NUV) excitation. The effect of Eu2+ and NH4Cl contents on photoluminescence properties and crystal phase formation have been investigated, respectively. The thermal stable property which is an important performance for LED application has also been measured. The emission intensity at 120 °C can maintain 94% of that at room temperature. Our results suggest that CaO: Eu2+ ceramic powder could be used as a promising blue emitting phosphor for NUV chip based white LEDs.
Co-reporter:Wen Liu, Zhendong Hao, Liangliang Zhang, Xia Zhang, Yongshi Luo, Guohui Pan, Huajun Wu, Jiahua Zhang
Journal of Alloys and Compounds 2017 Volume 696(Volume 696) pp:
Publication Date(Web):5 March 2017
DOI:10.1016/j.jallcom.2016.11.126
•Tm3+-Yb3+-Tm3+ efficient forward-backward energy transfer is proved.•BET is benefit from the preferential excitation in the step of FET.•Be propitious to Tm3+ blue upconversion with red light excitation.•A new method to calculate radiative rate of Tm3+:3H4 state is demonstrated.Under 808 nm excitation into the Tm3+:3H4 level, a considerable enhancement in intensity of Tm3+: 3F4→3H6 emission with respect to Tm3+: 3H4→3F4 emission is observed in Tm3+/Yb3+ codoped Lu1.6Sc0.4O3. The Tm3+-Yb3+-Tm3+ forward-backward energy transfer is proved to generate an additional route for the 3H4→3F4 nonradiative relaxation, that is, energy transfer from Tm3+:3H4 to Yb3+:2F5/2 and the subsequent back transfer from Yb3+:2F5/2 to Tm3+:3F4. The analysis of emission spectra reveals that back transfer from Yb3+ that excited by the forward energy transfer is more efficient than by absorption of 980 nm infrared light. The efficiency can reach as high as 96% with an extremely low Tm3+ concentration (0.05%). We propose that those Yb3+ ions with nearby Tm3+ ions in the forward energy transfer are preferentially excited instead of equally excited as by absorption of light. The efficiencies of the energy back transfer at different Yb3+ concentrations are evaluated, indicating that the forward-backward energy transfer can act as a dominant route for the Tm3+: 3H4→3F4 nonradiative relaxation when Yb3+ concentration is higher than 5%. A method to determine the radiative rate of Tm3+:3H4 state based on the model of cross relaxation is also demonstrated.
Co-reporter:Liangliang Zhang, Jiahua Zhang, Guo-Hui Pan, Xia Zhang, Zhendong Hao, Yongshi Luo, and Huajun Wu
Inorganic Chemistry 2016 Volume 55(Issue 19) pp:9736-9741
Publication Date(Web):September 12, 2016
DOI:10.1021/acs.inorgchem.6b01490
Luminescence property of low-concentration Eu2+-doped SrAlSi4N7:Ce3+ yellow phosphor is reported in this paper. Three optical centers Ce1, Ce2, and Eu2 are observed in the phosphor. Deconvolution of emission spectrum confirms the three centers to be green (530 nm), yellow (580 nm), and red (630 nm), respectively. This property promises considerable improvement of color-rendering property of a white light-emitting diode (wLED). For example, color-rendering index (CRI) of wLED fabricated by combining a blue LED chip and SrAlSi4N7:0.05Ce3+,0.01Eu2+ phosphor reaches 88. A competitive energy transfer process between Ce1–Ce2 and Ce1–Eu2 is confirmed based on Inokuti–Hirayama formula. Ratio of energy transfer rate between Ce1–Ce2 and Ce1–Eu2 (WCe1–Eu2/WCe1–Ce2) is calculated to be 2.0. This result reveals the effect of Eu2+ concentration on quantity of green and red components in SrAlSi4N7:Ce3+,Eu2+ phosphor.
Co-reporter:Leyu Feng, Zhendong Hao, Xia Zhang, Liangliang Zhang, Guohui Pan, Yongshi Luo, Ligong Zhang, Haifeng Zhao and Jiahua Zhang
Dalton Transactions 2016 vol. 45(Issue 4) pp:1539-1545
Publication Date(Web):07 Dec 2015
DOI:10.1039/C5DT04341G
CaO:Ce3+,Mn2+ phosphors with various Mn2+ concentrations were synthesized by a solid state reaction method. Efficient energy transfer from Ce3+ to Mn2+ was observed and it allows the emission color of CaO:Ce3+,Mn2+ to be continuously tuned from yellow (contributed by Ce3+) to red (by Mn2+) with an increase in Mn2+ concentration and upon blue light excitation. The red emission becomes dominant when the Mn2+ concentration is ≥0.014 with an energy transfer efficiency higher than 87% which can reach as high as 94% for a Mn2+ concentration of only 0.02. A critical distance of 10.5 Å for the Ce3+–Mn2+ energy transfer was determined. A faster decrease of Ce3+ luminescence intensity in comparison with its lifetime was observed on increasing the Mn2+ concentration. The analysis of this feature reveals that the Ce3+ excitation energy can be completely transferred to Mn2+ if the Ce3+–Mn2+ distance is shorter than 7.6 Å. A warm white LED was fabricated through integrating an InGaN blue LED chip and a blend of two phosphors (YAG:Ce3+ yellow phosphor and CaO:0.007Ce3+,0.014Mn2+ red phosphor) into a single package, which has CIE chromaticity coordinates of (x = 0.37, y = 0.35), a correlated color temperature of 3973 K and a color rendering index of 83.1. The results indicate that CaO:Ce3+,Mn2+ may serve as a potential red phosphor for blue LED based warm white LEDs.
Co-reporter:Jing Li, Li Chen, Zhendong Hao, Xia Zhang, Ligong Zhang, Yongshi Luo, and Jiahua Zhang
Inorganic Chemistry 2015 Volume 54(Issue 10) pp:4806-4810
Publication Date(Web):May 6, 2015
DOI:10.1021/acs.inorgchem.5b00280
An efficient near-infrared (NIR) downconversion has been demonstrated in CaSc2O4: Ce3+/Yb3+ phosphor. Doping concentration optimized CaSc2O4: 1%Ce3+/5%Yb3+ shows stronger NIR emission than doping concentration also optimized typical YAG: 1%Ce3+/5%Yb3+ under 470 nm excitation. The NIR emission from 900 to 1100 nm is enhanced by a factor of 2.4. In addition, the main emission peak of Yb3+ in the CaSc2O4 around 976 nm matches better with the optimal spectral response of the c-Si solar cell. The visible and NIR spectra and the decay curves of Ce3+: 5d → 4f emission were used to demonstrate the energy transfer from Ce3+ ions to Yb3+ ions. The downconversion phenomenon has been observed under the direct excitation of Ce3+ ions. On analyzing the dependence of energy transfer rate on Yb3+ ion concentration, we reveal that the energy transfer (ET) from Ce3+ ions to Yb3+ ions in CaSc2O4 occurs mainly by the single-step ET process. Considering that the luminescence efficiency of CaSc2O4: Ce3+ is comparable to that of commercial phosphor YAG: Ce3+, the estimated maximum energy transfer efficiency reaches 58% in the CaSc2O4: 1%Ce3+/15%Yb3+ sample, indicating that CaSc2O4: Ce3+/Yb3+ sample has the potential in improving the conversion efficiency of c-Si solar cells.
Co-reporter:Wenge Xiao; Xia Zhang; Zhendong Hao; Guo-Hui Pan; Yongshi Luo; Ligong Zhang
Inorganic Chemistry 2015 Volume 54(Issue 7) pp:3189-3195
Publication Date(Web):March 9, 2015
DOI:10.1021/ic502773t
Novel blue-emitting K2Al2B2O7:Eu2+ (KAB:Eu2+) phosphor was synthesized by solid state reaction. The crystal structural and photoluminescence (PL) properties of KAB:Eu2+ phosphor, as well as its thermal properties of the photoluminescence, were investigated. The KAB:Eu2+ phosphor exhibits broad excitation spectra ranging from 230 to 420 nm, and an intense asymmetric blue emission band centered at 450 nm under λex = 325 nm. Two different Eu2+ emission centers in KAB:Eu2+ phosphor were confirmed via their fluorescence decay lifetimes. The optimal concentration of Eu2+ ions in K2–xEuxAl2B2O7 was determined to be x = 0.04 (2 mol %), and the corresponding concentration quenching mechanism was verified to be the electric dipole–dipole interactions. The PL intensity of the nonoptimized KAB:0.04Eu2+ phosphor was measured to be ∼58% that of the commercial blue-emitting BaMgAl10O17:Eu2+ phosphor, and this phosphor has high color purity with the CIE coordinate (0.147, 0.051). When heated up to 150 °C, the KAB:0.04Eu2+ phosphor still has 82% of the initial PL intensity at room temperature, indicating its high thermal stability. These results suggest that the KAB:Eu2+ is a promising candidate as a blue-emitting n-UV convertible phosphor for application in white light emitting diodes.
Co-reporter:Guotao Xiang, Jiahua Zhang, Zhendong Hao, Xia Zhang, Guo-Hui Pan, Yongshi Luo, Wei Lü, and Haifeng Zhao
Inorganic Chemistry 2015 Volume 54(Issue 8) pp:3921-3928
Publication Date(Web):April 7, 2015
DOI:10.1021/acs.inorgchem.5b00109
Nanosized Yb3+ and Er3+ co-doped β-NaYF4 cores coated with multiple β-NaYF4 shell layers were synthesized by a solvothermal process. X-ray diffraction and scanning electron microscopy were used to characterize the crystal structure and morphology of the materials. The visible and near-infrared spectra as well as the decay curves were also measured. A 40-fold intensity increase for the green upconversion and a 34-fold intensity increase for the red upconversion were observed as the cores are coated with three shell layers. The origin of the upconversion enhancement was studied on the basis of photoluminescence spectra and decay times. Our results indicate that the upconversion enhancement in the sandwiched structure mainly originates from the suppression of de-excitation of Yb3+ ions. We also explored the population of the Er3+4F9/2 level. The results reveal that energy transfer from the lower intermediate Er3+4I13/2 level is dominant for populating the Er3+4F9/2 level when the nanocrystal size is relatively small; however, with increasing nanocrystal size, the contribution of the green emitting Er3+4S3/2 level for populating the Er3+4F9/2 level, which mainly comes from the cross relaxation energy transfer from Er3+ ions to Yb3+ ions followed by energy back transfer within the same Er3+–Yb3+ pair, becomes more and more important. Moreover, this mechanism takes place only in the nearest Er3+–Yb3+ pairs. This population route is in good agreement with that in nanomaterials and bulk materials.
Co-reporter:Guotao Xiang, Jiahua Zhang, Zhendong Hao, Xia Zhang, Guo-Hui Pan, Yongshi Luo and Haifeng Zhao
CrystEngComm 2015 vol. 17(Issue 16) pp:3103-3109
Publication Date(Web):16 Mar 2015
DOI:10.1039/C5CE00294J
The upconversion (UC) enhancement with size decrease has been realized through Y3+ ions doping in β-NaLuF4:Yb3+/Er3+ nanocrystals (NCs) by a solvothermal process. X-Ray diffraction (XRD), scanning electron microscopy (SEM) and UC luminescence spectra were used to characterize the resulting samples. With an increase of the Y3+ doping concentration, the NCs size is continuously decreased with no phase transition. Meanwhile, the UC intensity is firstly increased and then it decreases when the Y3+ ions concentration is over 30 mol%. The NCs (β-NaLu0.48Y0.3Yb0.2Er0.02F4) with the optimum Y3+ ions doping concentration (30 mol%) for UC emission have a diameter of about 80 nm. Compared with β-NaLu0.78Yb0.2Er0.02F4 and β-NaY0.78Yb0.2Er0.02F4 prepared under the same conditions, the green UC emission is enhanced by a factor of 1.8 and 16, respectively, for β-NaLu0.48Y0.3Yb0.2Er0.02F4. The variation of the UC intensity with the increasing Y3+ ions concentration is attributed to the changing of the symmetry of the local crystal field induced by Y3+ ions doping, which has been proved by the structural probe Eu3+ ions. For β-NaLu0.78Yb0.2Er0.02F4 and β-NaLu0.48Y0.3Yb0.2Er0.02F4, a three-photon green UC process and a three-photon red UC process occur simultaneously at high pump power density, which can be described as 4G11/2 (Er3+) + 4I15/2 (Er3+) → 2H11/2/4S3/2 (Er3+) + 4I13/2 (Er3+) and 4G11/2 (Er3+) + 2F7/2 (Yb3+) → 4F9/2 (Er3+) + 2F5/2 (Yb3+), respectively.
Co-reporter:Guotao Xiang, Jiahua Zhang, Zhendong Hao, Xia Zhang, Guo-Hui Pan, Li Chen, Yongshi Luo, Shaozhe Lü, Haifeng Zhao
Journal of Colloid and Interface Science 2015 Volume 459() pp:224-229
Publication Date(Web):1 December 2015
DOI:10.1016/j.jcis.2015.08.026
The Yb3+ and Er3+ codoped orthorhombic LuF3 rectangular nanocrystals (NCs) with the size of about 10 nm were synthesized by a facile and effective solvothermal process. X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), upconversion (UC) luminescence spectra and decay curves were used to characterize the resulting samples. Compared with YF3 and α-NaYF4 NCs, owning the similar size and the same doping levels of Yb3+ ions and Er3+ ions as LuF3 NCs, the green UC emission of LuF3 NCs is 18.7 times and 5.1 times stronger than that of YF3 and α-NaYF4 NCs respectively; the red UC emission of LuF3 NCs is 13.2 times and 0.6 times stronger than that of YF3 and α-NaYF4 NCs respectively. Under 980 nm wavelength excitation, the decay curves of both 4S3/2 → 4I15/2 transition and 4F9/2 → 4I15/2 transition exhibit a single exponential function, resulting from the fast energy migrations among Yb3+ ions caused by the high concentration of Yb3+ ions (20 mol%). Meanwhile, at relatively low power density, the slopes of the linear plots between log(I) and log(P) for green UC and red UC are 1.7 and 1.9 respectively, which are less than 2 due to the quenching of the thermal effect, indicating a two-photon process for them. At high power density, the slopes are decreased caused by the saturation effect. In addition, we proved the existence of the thermal effect by the pump power dependence of the intensity ratio of 2H11/2 → 4I15/2 transition to 4S3/2 → 4I15/2 transition.Compared with YF3 and α-NaYF4 NCs, owning the similar size and the same doping levels of Yb3+ ions and Er3+ ions as LuF3 NCs, the green UC emission of LuF3 NCs is 18.7 times and 5.1 times stronger than that of YF3 and α-NaYF4 NCs respectively; the red UC emission of LuF3 NCs is 13.2 times and 0.6 times stronger than that of YF3 and α-NaYF4 NCs respectively.
Co-reporter:Guo-Hui Pan, Tomokatsu Hayakawa, Masayuki Nogami, Zhendong Hao, Xia Zhang, Xuesong Qu and Jiahua Zhang
RSC Advances 2015 vol. 5(Issue 108) pp:88590-88601
Publication Date(Web):12 Oct 2015
DOI:10.1039/C5RA18292A
A heterobimetallic complex, zinc titanium glycolate acetate hydrate (Zn2Ti3–GAH), tentatively formulated as Zn2Ti3(OCH2CH2O)4(OCH2CH2OH)5(CH3COO)3·2HOCH2CH2OH·H2O, was synthesized by a room-temperature homogeneous precipitation in ethylene glycol solution. Its chemical composition, crystal structure, morphology, growth mechanism and thermal behaviors were characterized in detail. The precipitated Zn2Ti3–GAH was of a highly crystalline monoclinic phase and porous microrod morphology. As the single source precursor (SSP), Zn2Ti3–GAH was transformed into different phases of zinc titanate via thermal decomposition. With the remaining shape of the microrods, cubic phases of Zn2Ti3O8 and rutile TiO2 (r-TiO2) supported hexagonal phases of ZnTiO3 (h-ZnTiO3) were obtained by calcination at 500 and 700 °C, respectively; while r-TiO2 supported Zn2TiO4 were yielded in the form of dispersed particles or chains at higher temperature (950 °C). Benefiting from the SSP route and the confinement in the specific microrod domains of precursors, the heterostructures of r-TiO2–ZnTiO3 and r-TiO2–Zn2TiO4 were formed during programmable calcination. The studies on photocatalysis by degrading methylene blue (MB) under ultraviolet (UV) irradiation indicated that the as-transformed zinc titanate exhibited enhanced activity. In particular, r-TiO2 supported h-ZnTiO3 displayed the photodegradation reaction rate constant of 0.00163 s−1, which was comparable to that of commercially available Degussa P25 TiO2. This probably related to the more effective charge separation in the r-TiO2–ZnTiO3 heterostructure packed in the microrods.
Co-reporter: Jing Li;Zhendong Hao;Li Chen;Xia Zhang;Yongshi Luo
ChemPhysChem 2015 Volume 16( Issue 7) pp:1366-1369
Publication Date(Web):
DOI:10.1002/cphc.201500011
Abstract
Concentration-optimized CaSc2O4:0.2 % Ho3+/10 % Yb3+ shows stronger upconversion luminescence (UCL) than a typical concentration-optimized upconverting phosphor Y2O3:0.2 % Ho3+/10 % Yb3+ upon excitation with a 980 nm laser diode pump. The 5F4+5S25I8 green UCL around 545 nm and 5F55I8 red UCL around 660 nm of Ho3+ are enhanced by factors of 2.6 and 1.6, respectively. On analyzing the emission spectra and decay curves of Yb3+: 2F5/22F7/2 and Ho3+: 5I65I8, respectively, in the two hosts, we reveal that Yb3+ in CaSc2O4 exhibits a larger absorption cross section at 980 nm and subsequent larger Yb3+: 2F5/2Ho3+: 5I6 energy-transfer coefficient (8.55×10−17 cm3 s−1) compared to that (4.63×10−17 cm3 s−1) in Y2O3, indicating that CaSc2O4:Ho3+/Yb3+ is an excellent oxide upconverting material for achieving intense UCL.
Co-reporter:Jiahua Zhang, Zhendong Hao, Jing Li, Xia Zhang, Yongshi Luo and Guohui Pan
Light: Science & Applications 2015 4(1) pp:e239
Publication Date(Web):2015-01-01
DOI:10.1038/lsa.2015.12
The rare earth Er3+ and Yb3+ codoped system is the most attractive for showcasing energy transfer upconversion. This system can generate green and red emissions from Er3+ under infrared excitation of the sensitizer Yb3+. It is well known that the red-emitting state can be populated from the upper green-emitting state. The contribution of multiphonon relaxation to this population is generally considered important at low excitation densities. Here, we demonstrate for the first time the importance of a previously proposed but neglected mechanism described as a cross relaxation energy transfer from Er3+ to Yb3+, followed by an energy back transfer within the same Er3+–Yb3+ pair. A luminescence spectroscopy study of cubic Y2O3:Er3+, Yb3+ indicates that this mechanism can be more efficient than multiphonon relaxation, and it can even make a major contribution to the red upconversion. The study also revealed that the energy transfers involved in this mechanism take place only in the nearest Er3+–Yb3+ pairs, and thus, it is fast and efficient at low excitation densities. Our results enable a better understanding of upconversion processes and properties in the Er3+–Yb3+ system.
Co-reporter:Guotao Xiang, Jiahua Zhang, Zhendong Hao, Xia Zhang, Yongshi Luo, Shaozhe Lü and Haifeng Zhao
CrystEngComm 2014 vol. 16(Issue 12) pp:2499-2507
Publication Date(Web):07 Jan 2014
DOI:10.1039/C3CE42490A
Phase transition from hexagonal to cubic was successfully achieved through La3+ ions tridoping in NaLuF4:Yb3+/Er3+ nanocrystals (NCs) by a solvothermal process at 300 °C. X-Ray diffraction (XRD) patterns, scanning electron microscopy (SEM) images, transmission electron microscopy (TEM) images, Fourier-transform infrared (FTIR) absorption spectra, upconversion (UC) luminescence spectra and decay curves were used to characterize the resulting samples. Compared to cubic phase α-NaLu0.78Yb0.2Er0.02F4 NCs which are similar in size and prepared at normal temperature (280 °C), the number of the surface organic groups such as hydroxyl group (–OH) attached on NaLu0.48La0.3Yb0.2Er0.02F4 NCs is reduced. Furthermore, the green UC emission increases and simultaneously the red UC emission decreases. The UC mechanisms were studied by power-intensity log dependence. It indicates that in both of the two samples, the red UC emission is a two-photon process when the excitation power density is low, but a three-photon process occurs when the excitation power density is high. However, the green UC emission is a two-photon process all the time both at low or high excitation power density. Through analyzing the luminescence decay curves of the 4S3/2 → 4I15/2 transition and 4F9/2 → 4I15/2 transition under the 980 nm excitation wavelength, it is concluded that the population of the 4F9/2 level originates from the 4I13/2 level, not from the 2H11/2/4S3/2 level in the two samples.
Co-reporter:Guotao Xiang, Jiahua Zhang, Zhendong Hao, Xia Zhang, Guohui Pan, Yongshi Luo, Shaozhe Lü and Haifeng Zhao
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 20) pp:9289-9293
Publication Date(Web):03 Apr 2014
DOI:10.1039/C4CP01184H
The Pr3+ and Yb3+ codoped β-NaLuF4 hexagonal nanoplates with a size of 250 nm × 110 nm were synthesized by a solvothermal process. X-Ray diffraction and scanning electron microscopy were used to characterize the crystal structure and morphology of the materials. The visible and near infrared spectra as well as the decay curves of Pr3+:3P0 level were used to demonstrate the energy transfer from Pr3+ ions to Yb3+ ions. The downconversion phenomenon has been observed under the direct excitation of the 3P2 level of Pr3+. According to the analysis of the dependence of the initial transfer rate upon Yb3+ ion concentration, it indicates that the ET from Pr3+ ions to Yb3+ ions is only by a two-step ET process when the Yb3+ concentration is very low; however, with the increase of the Yb3+ concentration, a cooperative ET process occurs and gradually increases; when the Yb3+ ion concentration increases to 20 mol%, the ET from Pr3+ ions to Yb3+ ions occurs only by the cooperative ET process. When the doping concentration of Yb3+ ions reaches 20 mol% at a fixed concentration of Pr3+ ions (1 mol%), the theoretical quantum efficiency is 192.2%, close to the limit of 200%. The current research has great potential in improving the conversion efficiency of silicon solar cells.
Co-reporter:Jun Qiao, Jiahua Zhang, Xia Zhang, Zhendong Hao, Yongfu Liu and Yongshi Luo
Dalton Transactions 2014 vol. 43(Issue 10) pp:4146-4150
Publication Date(Web):26 Nov 2013
DOI:10.1039/C3DT52902A
The energy transfer and luminescence properties in the Ce3+ and Pr3+ co-activated Ca3Sc2Si3O12 (CSS) silicate garnet are studied in our work. The addition of Pr3+ exhibits a red emission around 610 nm in the green phosphor CSS:Ce3+, but the amount of Pr3+ incorporated into the phosphor is very limited due to the charge mismatch when Pr3+ substitutes for Ca2+ in CSS. In order to promote Pr3+ incorporation into CSS lattices to enhance the red emission component, the addition of Mg2+ incorporated into Sc3+ site is performed to compensate the residual positive charge caused by the substitution of Pr3+ for Ca2+ in CSS. Finally, a white LED with color rendering index of 80 and correlated color temperature of 8715 K is obtained by combining the single CSS:0.05Ce3+, 0.01Pr3+, 0.3Mg2+ phosphor with a blue-emitting InGaN LED chip.
Co-reporter:Xia Zhang, Yongfu Liu, Jian Lin, Zhendong Hao, Yongshi Luo, Qingzhe Liu, Jiahua Zhang
Journal of Luminescence 2014 Volume 146() pp:321-324
Publication Date(Web):February 2014
DOI:10.1016/j.jlumin.2013.10.017
Co-reporter:Xiaoling Dong, Jiahua Zhang, Xia Zhang, Zhendong Hao, Yongshi Luo
Journal of Luminescence 2014 Volume 148() pp:60-63
Publication Date(Web):April 2014
DOI:10.1016/j.jlumin.2013.11.083
•A novel Sr9Sc(PO4)7: Ce3+, Mn2+ phosphor has been synthesized and investigated.•Energy transfer from sensitizer Ce3+ to activator Mn2+ in Sr9Sc(PO4)7 host has been studied.•The emission color of the phosphors can be easily modulated from blue to reddish orange.•Results indicated that Sr9Sc(PO4)7: Ce3+, Mn2+ may serve as a potential color-tunable phosphor for UV-LEDs.A series of Ce3+ and Mn2+ co-doped Sr9Sc(PO4)7 phosphors have been synthesized by high temperature solid state reaction and their luminescence properties are investigated. The obtained phosphors exhibit a broad excitation band ranging from 240 to 350 nm and two emission bands centered at about 370 and 610 nm upon 310 nm excitation, resulting from the 5d–4f transitions of Ce3+ and the d–d forbidden transition of Mn2+, respectively. Energy transfer mechanism from Ce3+ to Mn2+ in Sr9Sc(PO4)7 host matrix was studied and demonstrated to be a resonant type via a dipole–dipole mechanism based on the decay lifetime data. Furthermore, we have calculated the critical distance for Ce3+→Mn2+ energy transfer to be about 6.12 Å by the spectral overlap method. Through effective energy transfer, a color-tunable emission varied from blue to reddish orange can be realized by adjusting the ratio of Ce3+ to Mn2+. Our results indicate the novel Sr9Sc(PO4)7: Ce3+, Mn2+ phosphor can be a promising candidate for a color-tunable phosphor applied in a UV white light emitting diodes.
Co-reporter:Xiaoling Dong;Liangliang Zhang;Xia Zhang;Zhendong Hao;Yongshi Luo
European Journal of Inorganic Chemistry 2014 Volume 2014( Issue 5) pp:870-874
Publication Date(Web):
DOI:10.1002/ejic.201301216
Abstract
Eu2+–Mn2+ codoped yellow-emitting Sr9Sc(PO4)7 (SSP) phosphors have been synthesized by solid-state reactions. The synthesis, structure refinement, and luminescence properties of the obtained phosphor were investigated in detail. The obtained phosphor exhibits a strong excitation band between 250 and 450 nm, matching well with the dominant emission band of a near-UV light-emitting-diode (LED) chip. Upon excitation at 365 nm, the Sr9Sc(PO4)7:Eu2+, Mn2+ phosphor shows strong yellow emissions centered at 510 and 610 nm. The energy transfer mechanism from Eu2+ to Mn2+ in Sr9Sc(PO4)7:Eu2+, Mn2+ has been studied and demonstrated to be a resonant type through a dipole-quadrupole mechanism based on the decay lifetime data. These results indicate that yellow-emitting Sr9Sc(PO4)7:Eu2+, Mn2+ can serve as a promising candidate for application in white-light LEDs.
Co-reporter:Xiaoling Dong, Jiahua Zhang, Xia Zhang, Zhendong Hao, Shaozhe Lv
Ceramics International 2014 Volume 40(Issue 4) pp:5421-5423
Publication Date(Web):May 2014
DOI:10.1016/j.ceramint.2013.10.124
Abstract
A series of Eu2+-activated Sr9Sc(PO4)7 yellowish-green emitting phosphors were synthesized by conventional solid-state reaction. The photoluminescence (PL) properties and concentration quenching mechanism of the as-prepared phosphors were investigated. The emission spectrum exhibits a broad and asymmetric band peaking at 510 nm, which corresponds to the 4f65d1→4f7 transition of Eu2+. The excitation spectrum exhibits a broad band extending from 250 to 450 nm, which matches well with the emission of near ultraviolet (n-UV) chips (350–430 nm). Non-radiative transitions between Eu2+ ions in the Sr9Sc(PO4)7 host have been demonstrated to be attributable to dipole–dipole interactions, and the critical distance was calculated to be 23.1 Å. These results indicate that Sr9Sc(PO4)7:Eu2+ phosphor could serve as a promising candidate for application in n-UV white-light LEDs.
Co-reporter:Xiaoling Dong, Jiahua Zhang, Xia Zhang, Zhendong Hao, Yongshi Luo
Journal of Alloys and Compounds 2014 Volume 587() pp:493-496
Publication Date(Web):25 February 2014
DOI:10.1016/j.jallcom.2013.10.116
•A novel orange–red phosphor Sr9Sc(PO4)7:Eu3+ has been synthesized and investigated.•The phosphors can be effectively excited by near UV (394 nm) light.•The thermal quenching temperature of Sr9Sc(PO4)7:Eu3+ is above 200 °C.A series of Eu3+ ions doped Sr9Sc(PO4)7 orange–red emitting phosphors have been prepared by solid-state reaction method. Photoluminescence properties under near-ultraviolet (NUV) light excitation of the samples have been carried out. The studies show that the samples can be effectively excited by NUV (394 nm) which matches to the output wavelengths of near UV chips and exhibits intense orange–red emissions. Eu3+ concentration was found to be optimum at x = 0.4 and the thermal quenching temperature of Sr9Sc(PO4)7:0.4Eu3+ is above 200 °C. Thus, the intense orange red emitting phosphor could be a promising phosphor candidate in generating white light combined with the NUV chip.
Co-reporter:Jing Li, Jiahua Zhang, Xia Zhang, Zhendong Hao, Yongshi Luo
Journal of Alloys and Compounds 2014 Volume 583() pp:96-99
Publication Date(Web):15 January 2014
DOI:10.1016/j.jallcom.2013.08.125
An efficient near infrared (NIR) quantum cutting in CaSc2O4: Tm3+/Yb3+ phosphor has been demonstrated by the visible and NIR spectra properties as well as the decay curves of Tm3+:1G4 level. Upon excitation of Tm3+:1G4 level with a blue photon at 466 nm, Yb3+:2F5/2 level can emit two NIR photons around 1000 nm through cooperative energy transfer (ET) from Tm3+ to Yb3+ with the maximum energy transfer efficiency is 71%, and highest theoretical quantum efficiency reaches 171%, close to the limit of 200%. Because the energy of Yb3+ transition is matched well with band gap of crystalline silicon, the excellent downconversion luminescence property indicates that CaSc2O4:Tm3+/Yb3+ is a promising oxide material for increasing the conversion efficiency of crystalline silicon solar cells.
Co-reporter:Zhendong Hao, Jiahua Zhang, Xia Zhang, Yongshi Luo, Ligong Zhang, Haifeng Zhao
Journal of Luminescence 2014 152() pp: 40-43
Publication Date(Web):
DOI:10.1016/j.jlumin.2013.10.033
Co-reporter:Liangliang Zhang, Jiahua Zhang, Xia Zhang, Zhendong Hao, Haifeng Zhao, and Yongshi Luo
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 24) pp:12839
Publication Date(Web):November 20, 2013
DOI:10.1021/am402612n
Synthesis and luminescent properties of Ce3+-doped SrAlSi4N7 yellow-emitting phosphor are reported. In comparison with YAG: Ce3+, the phosphor exhibits smaller thermal quenching and a broader emission band centering at 555 nm with a bandwidth as large as 115 nm, being suitable for fabricating high color rendering white LED. It is observed in material synthesis that intense luminescence can be achieved only in case of excessive AlN in the raw materials. The role of the excessive AlN is studied. The mechanism for existence of edge-sharing [AlN4] tetrahedral, which is unreasonable according to the aluminum avoidance principle, is discussed in detail.Keywords: crystal chemistry; excessive AlN; luminescent property; nitridosilicate; phosphor; preferred orientation;
Co-reporter:Jing Li, Zhendong Hao, Xia Zhang, Yongshi Luo, Jihong Zhao, Shaozhe Lü, Jian Cao, Jiahua Zhang
Journal of Colloid and Interface Science 2013 Volume 392() pp:206-212
Publication Date(Web):15 February 2013
DOI:10.1016/j.jcis.2012.09.076
Single phase β-NaGdF4:Yb3+/Tm3+ and β-NaGdF4:Yb3+/Ho3+ submicron crystals with various morphologies including hexagonal prisms, spindles, and spheres were synthesized via the one-step hydrothermal method by controlling the pH values and sort of chelators (EDTA and citric acid). The prepared products showed intense up-converted luminescence (UCL) pumped by infrared laser at 980 nm. The hexagonal prisms that meaning high degree crystallinity demonstrated strong UCL in comparison with other morphologies such as spindles and spheres. In β-NaGdF4:Yb3+/Tm3+, UCL not only appeared transitions from 1G4, 1D2, and 1I6 states to the lower lying states of Tm3+, but also 6PJ → 8S7/2 transition (310 nm) of Gd3+. These UCL were responsible for three, five, and six photons processes determined by pump power dependence of UCL intensities. The observation of UCL of Gd3+ implied occurrence of energy transfer from Tm3+:1I6 to Gd3+:6PJ.Graphical abstractHighlights► β-NaGdF4 of hexagonal prisms, spindles, and spheres was synthesized. ► Regular hexagonal prisms have intense UCL. ► Gd3+:6PJ → 8S7/2 transition was found. ► Different spectral distributions for different morphologies were reported.
Co-reporter:Yongfu Liu, Xia Zhang, Zhendong Hao, Yongshi Luo, Xiaojun Wang, Li Ma, Jiahua Zhang
Journal of Luminescence 2013 Volume 133() pp:21-24
Publication Date(Web):January 2013
DOI:10.1016/j.jlumin.2011.12.052
Expanded emission spectra ranging from green to red are reported in Ca3Sc2Si3O12 (CSS):Ce3+,Mn2+ silicate garnets. Mn2+ may occupy Ca2+ site (Mn2+(I)) to generate a yellow emission band at 574 nm or Sc3+ site (Mn2+(II)) with red emission band at 680 nm. Efficient energy transfers from the green emitting Ce3+ to both Mn2+(I) and Mn2+(II) occur upon blue excitation into Ce3+. Concentration dependence of Mn2+ emission is analyzed based on Ce3+–Mn2+ energy transfer, steady state rate equations, and fluorescence lifetimes. Energy transfer efficiency (ηT) and rate (W) are calculated with values as high as 45% and 14.01×106 s−1, respectively.Highlights► Mn2+ can occupy Ca2+ site to generate a yellow emission band at 574 nm in Ca3Sc2Si3O12 (CSS). ► Mn2+ can also occupy Sc3+ site to generate a red emission band at 680 nm in CSS. ► Remarkable energy transfers (ETs) from Ce3+ to Mn2+ occur upon blue excitation into Ce3+ in CSS. ► Full color emissions are obtained based on Ce3+–Mn2+ ETs in CSS:Ce3+,Mn2+.
Co-reporter:Jing Li, Jiahua Zhang, Zhendong Hao, Xia Zhang, Jihong Zhao, Shaozhe Lü, Yongshi Luo
Inorganic Chemistry Communications 2013 Volume 38() pp:119-122
Publication Date(Web):December 2013
DOI:10.1016/j.inoche.2013.10.012
•CaSc2O4:Tm3 +/Yb3 + submicro-rod was synthesized by solvothermal and annealing method.•The temperature of formed pure phase is as low as 600 °C.•The size of submicro-rod is 35 nm in width and 200 nm in length.•Samples prepared show the strong upconversion luminescence.CaSc2O4: Tm3 +/Yb3 + submicro-rods were synthesized using the mild solvothermal and annealing technique. The temperature of formed pure phase is as low as 600 °C. The synthesized submicro-rods are uniform in size and shape. The size of rod is only small with 35 nm in width and 200 nm in length, which favors the application in biological assays and medical image. Furthermore, samples prepared exhibit the stronger upconversion luminescence than that of obtained by conventional solid state reaction method under 980 nm excitation. The near infrared emission around 800 nm is enhanced twofold closely. CaSc2O4 phosphor synthesized through the solvothermal and annealing method is a promising submicron upconversion material. The solvothermal and annealing technique is a suitable method for preparing CaSc2O4 sample with rod-like morphology.The rod-like CaSc2O4: Tm3 +/Yb3 + phosphors were firstly synthesized using the mild solvothermal and annealing technique. The synthesized submicro-rods are uniform in size and shape of which the size is only small with 35 nm in width and 200 nm in length.
Co-reporter:Zhendong Hao, Xia Zhang, Yongshi Luo, Ligong Zhang, Haifeng Zhao, Jiahua Zhang
Journal of Luminescence 2013 140() pp: 78-81
Publication Date(Web):
DOI:10.1016/j.jlumin.2013.03.013
Co-reporter:Dr. Jing Li; Jiahua Zhang;Dr. Zhendong Hao;Xia Zhang;Dr. Jihong Zhao;Dr. Yongshi Luo
ChemPhysChem 2013 Volume 14( Issue 18) pp:4114-4120
Publication Date(Web):
DOI:10.1002/cphc.201300842
Abstract
The optical properties of a Ho3+/Yb3+ co-doped CaSc2O4 oxide material are investigated in detail. The spectral properties are described as a function of doping concentrations. The efficient Yb3+Ho3+ energy transfer is observed. The transfer efficiency approaches 50 % before concentration quenching. The concentration-optimized sample exhibits a strong green emission accompanied with a weak red emission, showing perfect green monochromaticity. The results of the spectral distribution, power dependence, and lifetime measurements are presented. The green, red, and near-infrared (NIR) emissions around 545, 660, and 759 nm are assigned to the 5F4+5S25I8, 5F55I8, and 5F4+5S25I7 transitions of Ho3+, respectively. The detailed study reveals the upconversion luminescence mechanism involved in a novel Ho3+/Yb3+ co-doped CaSc2O4 oxide material.
Co-reporter:Jinying Yu, Xia Zhang, Zhendong Hao, Yongshi Luo, XiaoJun Wang, Jiahua Zhang
Journal of Alloys and Compounds 2012 Volume 515() pp:39-43
Publication Date(Web):25 February 2012
DOI:10.1016/j.jallcom.2011.10.043
Sr2−xCaxP2O7:Eu2+ (x = 0 − 2) phosphors with intense and adjustable blue emission are prepared by solid state reaction. The crystal phase evolution and correlated photoluminescence properties are studied as a function of Ca2+ content based on the experimental measurements of X-ray diffraction, photoluminescence and fluorescence decay. Our results indicate that Sr2−xCaxP2O7:Eu2+ crystallize in single α-Sr2P2O7 type phase for x ≤ 0.75. As increasing x from 0.75, α-Ca2P2O7 type phase starts to form and increase followed by reduction of α-Sr2P2O7 type phase. The single α-Ca2P2O7 type phase is obtained only at x = 2. The emission band (band I) in α-Sr2P2O7 type phase and that (band II) in α-Ca2P2O7 type phase both shift to the red on increasing x due to enhancement of crystal field strength in case of Ca2+ substitution for Sr2+. This substitution also leads to remarkably inhomogeneous broadening of band I, within which energy transfer from the high energy Eu2+ to the low energy one is observed. The superposition of band I and band II results in various distributions of intense emission band including the redshifted and more broadened ones suitable for white light generation.
Co-reporter:Wei Lü, Xia Zhang, Ying Wang, Zhendong Hao, Yongfu Liu, Yongshi Luo, Xiaojun Wang, Jiahua Zhang
Journal of Alloys and Compounds 2012 Volume 513() pp:430-435
Publication Date(Web):5 February 2012
DOI:10.1016/j.jallcom.2011.10.065
Eu2+ and Eu2+–Mn2+ codoped (Ba,Sr)Mg2Al6Si9O30 phosphors have been synthesized by solid state reaction, and their luminescent properties are investigated. Under the excitation of 330 nm, it is observed that the emission of Eu2+ consists of two emission bands, located at around 370 and 450 nm, which are attributed to two Eu2+ centers (Eu2+(I) and Eu2+(II)) ions substituting for two different Ba2+ and Mg2+ sites, respectively. As Sr2+ gradually substitutes Ba2+, the emission bands of Eu2+(I) shift to longer wavelength whereas the emission bands of Eu2+(II) exhibit no change. This phenomenon is discussed in terms of the crystal-field strength. A detail analysis on the energy transfer from Eu2+ to Mn2+ in SrMg2Al6Si9O30 host is presented, which indicates the energy of the red emission of Mn2+ is derived mainly from Eu2+(I). We have also demonstrated that BaMg2Al6Si9O30:Eu2+, Mn2+ exhibits better thermal quenching properties than that of SrMg2Al6Si9O30:Eu2+, Mn2+ because of bigger activation energy.Highlights► (Ba,Sr)Mg2Al6Si9O30:Eu2+ and (Ba,Sr)Mg2Al6Si9O30:Eu2+, Mn2+ phosphors have been synthesized by solid state reaction. ► Their luminescence properties are investigated and their origins are to be revealed. ► Energy transfer from Eu2+ to Mn2+ in SrMg2Al6Si9O30 is systematically investigated. ► Thermal quenching properties of BaMg2Al6Si9O30:Eu2+, Mn2+ and SrMg2Al6Si9O30:Eu2+, Mn2+ are studied.
Co-reporter:Yongfu Liu, Xia Zhang, Zhendong Hao, Yongshi Luo, XiaoJun Wang, Jiahua Zhang
Journal of Luminescence 2012 Volume 132(Issue 5) pp:1257-1260
Publication Date(Web):May 2012
DOI:10.1016/j.jlumin.2011.12.060
The yellow-emitting phosphor [Ca3−(x+0.06)LuxCe0.06](Sc2−yMgy)Si3O12 obtained from Lu3+ and Mg2+ co-modified green-emitting silicate garnet Ca3Sc2Si3O12:Ce3+ (CSS:Ce3+) exhibits promising applications for white LEDs. In this paper, we discuss the effect of charge balance on the garnet structure formation. The changes of bond length and covalence caused by the replacement of Lu3+ and Mg2+ for Ca2+ and Sc3+ are analyzed. The shift of the Ce3+ emission and excitation can be attributed to the combined results from crystal field splitting effect and centroid shift of Ce3+ 5d levels. Thermal stability is analyzed according to configurational coordinate diagram.Highlights► Charge balance plays an important role on the garnet structure formation. ► Bond lengths and polarizability affect the position of Ce3+ emission and excitation. ► Thermal quenching is analyzed based on configurational coordinate diagram. ► Our results provide an optimization method for phosphors used for white LEDs.
Co-reporter:Wei Lü, Yongshi Luo, Zhendong Hao, Xia Zhang, Xiaojun Wang, Jiahua Zhang
Journal of Luminescence 2012 Volume 132(Issue 9) pp:2439-2442
Publication Date(Web):September 2012
DOI:10.1016/j.jlumin.2012.04.016
BaMg2Al6Si9O30:Eu2+ phosphors are synthesized by the solid-state reaction method and their photoluminescence (PL) properties are investigated. The ultraviolet emission originates from Eu2+(I) substituting for Ba2+ sites, whereas the blue emission is attributed to Eu2+(II) substituting for Mg2+ sites. With increasing Eu2+ doping concentrations, the blue emission band shifts to long wavelength and the PL intensity ratio of blue to ultraviolet emission increases. Energy transfer between the two different Eu2+ ions is analyzed by photoluminescence excitation and emission spectra, and lifetimes. Results indicate that the emission spectra can be tuned by changing Eu2+ contents. We have also demonstrated that BaMg2Al6Si9O30:Eu2+ phosphor is a kind of potential phosphor for fluorescent lamps.Highlights► BaMg2Al6Si9O30:Eu2+ phosphors are synthesized by the solid-state reaction method. ► PL intensity ratio of blue–ultraviolet emission increases with increasing Eu2+ contents. ► A redshift in the blue emission is observed with increasing Eu2+ contents. ► Energy transfer among Eu2+ ions is analyzed. ► They are promising phosphors for fluorescent lamps.
Co-reporter:Wei Lü, Yongshi Luo, Zhendong Hao, Xia Zhang, Xiaojun Wang, Jiahua Zhang
Materials Letters 2012 Volume 77() pp:45-47
Publication Date(Web):15 June 2012
DOI:10.1016/j.matlet.2012.02.095
Ce3 + and Mn2 + co-doped Ca4Si2O7F2 phosphors have been synthesized by high temperature solid state reaction and their luminescence properties are investigated. The effect of Ce3 + concentration on the emission intensity of Ca4Si2O7F2: Ce3 + is studied, and the emission intensity reaches a maximum at 4% Ce3 +. Energy transfer from Ce3 + to Mn2 + is observed. The emission spectra of the phosphors show a blue broad band at 460 nm of Ce3 + and a yellow band at 580 nm of Mn2 +, originate from the allowed 5d → 4f transition of the Ce3 + ion and the 4T1g(4G) → 6A1g(6S) transition of the Mn2 + ion, respectively. Results indicate that the varied emitted color from blue to yellow can be achieved by tuning the relative ratio of the Ce3 + to Mn2 + ions based on the principle of energy transfer. We have demonstrated that Ca4Si2O7F2: Ce3 +, Mn2 + phosphors can be a promising candidate for a color-tunable phosphor applied in a near-UV White light emitting diodes.Highlights► A new dual-tunable Ca4Si2O7F2:Ce3+, Mn2+ phosphor are synthesized. ► Energy transfer from sensitizer Ce3+ to activator Mn2+ in Ca4Si2O7F2 host has been studied. ► The emission color of the phosphors can be easily modulated from blue to yellow. ► Results indicated that Ca4Si2O7F2:Ce3+, Mn2+ may serve as a potential color-tunable phosphor for NUV- LEDs.
Co-reporter:Xia Zhang, Yongfu Liu, Zhendong Hao, Yongshi Luo, Xiaojun Wang, Jiahua Zhang
Materials Research Bulletin 2012 47(5) pp: 1149-1152
Publication Date(Web):
DOI:10.1016/j.materresbull.2012.02.013
Co-reporter:Yongfu Liu, Xia Zhang, Zhendong Hao, Yongshi Luo, XiaoJun Wang and Jiahua Zhang
Journal of Materials Chemistry A 2011 vol. 21(Issue 41) pp:16379-16384
Publication Date(Web):13 Sep 2011
DOI:10.1039/C1JM11601K
We report luminescence properties of Ce3+ and Mn2+ co-activated Ca3Sc2Si3O12 (CSS) silicate garnets. It is observed that Mn2+ may not only occupy Ca2+ sites to generate a yellow emission (Mn2+(I)) at 574 nm but also Sc3+ sites to generate a red emission (Mn2+(II)) at 680 nm. Considerable Mn2+ substitution for Sc3+ can be performed through balancing their charge difference by introducing a trivalent rare earth ion, such as La3+ and Ce3+, to replace Ca2+. Meanwhile, remarkable energy transfer from the green emitting Ce3+ to both Mn2+(I) and Mn2+(II) can occur, making tunable color and white light emission available in CSS:Ce3+,Mn2+ upon blue excitation into Ce3+. White LEDs combined by CSS:Ce3+,Mn2+ phosphors and blue LED chips are fabricated. A CSS:0.03Ce3+,0.2Mn2+ phosphor with deficient red emission is enriched in red by increasing Ce3+ concentration to 0.1, which leads to increase of Mn2+(II) number in case of charge compensation by more Ce3+ ions. Consequently, the color rendering index of the white LEDs is improved from 64 to 76. The results of this work indicate that CSS:Ce3+,Mn2+ garnet could be a promising single phase phosphor for white LEDs.
Co-reporter:Yongfu Liu, Xia Zhang, Zhendong Hao, Xiaojun Wang and Jiahua Zhang
Journal of Materials Chemistry A 2011 vol. 21(Issue 17) pp:6354-6358
Publication Date(Web):22 Mar 2011
DOI:10.1039/C0JM04404K
Adding Si3N4 into green emitting Ca3Sc2Si3O12:Ce3+ garnet phosphor generates an additionally red emission band peaking around 610 nm that are assigned to Ce3+ ions having N3− in their local coordination. The excitation spectrum of the red band consists of not only a distinct band at 510 nm of itself but also an intense blue band at 450 nm that belongs to the typical Ce3+ ions with green emission, indicating a notable energy transfer from the green emitting Ce3+ ions to the red ones. The energy transfer significantly enables the achievement of a broad emission spectrum covering a red and green spectral region suitable for generating white light upon a blue light-emitting diode (LED) excitation. The decay patterns of the red and green fluorescence are discussed in relation to the effect of energy transfer. A white LED with high color rendering of 86 and low correlated color temperature of 4700 K is fabricated using the present single garnet phosphor.
Co-reporter:Yanping Li, Jiahua Zhang, Yongshi Luo, Xia Zhang, Zhendong Hao and Xiaojun Wang
Journal of Materials Chemistry A 2011 vol. 21(Issue 9) pp:2895-2900
Publication Date(Web):10 Jan 2011
DOI:10.1039/C0JM03394D
We synthesized a series of Yb3+, Er3+ and Tm3+ tri-doped Lu2O3 nanocrystals with various dopant concentrations by the hydrothermal approach. Due to a unique electronic state at the top of the valence band, Lu2O3 based materials exhibit intense upconversion luminescence involving 1G4 → 3H6 of Tm3+ in blue, (2H11/2, 4S3/2) → 4I15/2 in green and 4F9/2 → 4I15/2 in red of Er3+ upon near infrared excitation at 980 nm. The variation of upconversion spectra and color points with dopant concentrations and pump densities are studied in detail on the basis of energy transfer processes. An ideal white upconversion light with color coordinates of (0.327, 0.339) is obtained by controlling the intensity of red, green, and blue emission in Lu1.906Yb0.08Er0.008Tm0.006O3nanocrystals under a pump density of 8 W cm−2. Based on the present experimental data, we may predict the dopant concentrations and pump densities for any color point within or around the white light region in the tri-doped Lu2O3 nanocrystals.
Co-reporter:Jinying Yu, Zhendong Hao, Xia Zhang, Yongshi Luo and Jiahua Zhang
Chemical Communications 2011 vol. 47(Issue 45) pp:12376-12378
Publication Date(Web):20 Oct 2011
DOI:10.1039/C1CC15657H
Eu2+ singly and Eu2+, Mn2+ co-doped Sr2Mg3P4O15 exhibit not only the well known blue emission band of Eu2+ peaking at 448 nm but also a new band at 399 nm in violet. They are attributed to Eu2+ on different Sr2+ sites. The Eu2+ for the violet band can transfer energy to the red emitting Mn2+ more efficiently than Eu2+ for the blue band. The new Eu2+ band could enable Sr2Mg3P4O15:Mn2+, Eu2+ to be a promising phosphor for enriching the red component of white LEDs.
Co-reporter:Yongfu Liu, Xia Zhang, Zhendong Hao, Xiaojun Wang and Jiahua Zhang
Chemical Communications 2011 vol. 47(Issue 38) pp:10677-10679
Publication Date(Web):02 Sep 2011
DOI:10.1039/C1CC14324G
A tunable full-color-emitting Ca3Sc2Si3O12:Ce3+, Mn2+ (CSS:Ce3+,Mn2+) phosphor is obtained by addition of doped ions as charge compensation. White LEDs with high Ra (> 90) are achieved using the single CSS:Ce3+,Mn2+ phosphor.
Co-reporter:Wei Lü, Zhendong Hao, Xia Zhang, Yongshi Luo, Xiaojun Wang, and Jiahua Zhang
Inorganic Chemistry 2011 Volume 50(Issue 16) pp:7846-7851
Publication Date(Web):July 19, 2011
DOI:10.1021/ic201033e
A series of single-phase full-color emitting BaMg2Al6Si9O30:Eu2+, Tb3+, Mn2+ phosphors has been synthesized by solid-state reaction. Energy transfer from Eu2+ to Tb3+ and Eu2+ to Mn2+ in BaMg2Al6Si9O30 host matrix is studied by luminescence spectra and energy-transfer efficiency and lifetimes. The wavelength-tunable white light can be realized by coupling the emission bands centered at 450, 542, and 610 nm ascribed to the contribution from Eu2+ and Tb3+ and Mn2+, respectively. By properly tuning the relative composition of Tb3+/Mn2+, chromaticity coordinates of (0.31, 0.30), high color rendering index Ra = 90, and correlated color temperature (CCT) = 5374 K can be achieved upon excitation of UV light. Thermal quenching properties reveal that BaMg2Al6Si9O30: Eu2+, Tb3+, Mn2+ exhibits excellent characteristics even better than that of YAG:Ce. Our results indicate our white BaMg2Al6Si9O30:Eu2+, Tb3+, Mn2+ can serve as a key material for phosphor-converted light-emitting diode and fluorescent lamps.
Co-reporter:Jiahua Zhang, Lei Wang, Ye Jin, Xia Zhang, Zhendong Hao, Xiao-jun Wang
Journal of Luminescence 2011 Volume 131(Issue 3) pp:429-432
Publication Date(Web):March 2011
DOI:10.1016/j.jlumin.2010.09.011
Non-radiative energy transfers (ET) from Ce3+ to Pr3+ in Y3Al5O12:Ce3+, Pr3+ and from Sm3+ to Eu3+ in CaMoO4:Sm3+, Eu3+ are studied based on photoluminescence spectroscopy and fluorescence decay patterns. The result indicates an electric dipole–dipole interaction that governs ET in the LED phosphors. For Ce3+ concentration of 0.01 in YAG:Ce3+, Pr3+, the rate constant and critical distance are evaluated to be 4.5×10−36 cm6 s−1 and 0.81 nm, respectively. An increase in the red emission line of Pr3+ relative to the yellow emission band of Ce3+, on increasing Ce3+ concentration is observed. This behavior is attributed to the increase of spectral overlap integrals between Ce3+ emission and Pr3+ excitation due to the fact that the yellow band shifts to the red spectral side with increasing Ce3+ concentration. In CaMoO4:Sm3+, Eu3+, Sm3+–Eu3+ transfer occurs from 4G5/2 of Sm3+ to 5D0 of Eu3+. The rate constant of 8.5×10−40 cm6 s−1 and the critical transfer distance of 0.89 nm are evaluated.
Co-reporter:Wei Lü, Zhendong Hao, Xia Zhang, Yongshi Luo, Xiaojun Wang, Jiahua Zhang
Journal of Luminescence 2011 Volume 131(Issue 11) pp:2387-2390
Publication Date(Web):November 2011
DOI:10.1016/j.jlumin.2011.05.065
Eu2+ and Mn2+ co-doped Ca8Zn(SiO4)4Cl2 phosphors have been synthesized by a high temperature solid state reaction. Energy transfer from Eu2+ to Mn2+ is observed. The emission spectra of the phosphors show a green band at 505 nm of Eu2+ and a yellow band at 550 nm of Mn2+. The excitation spectra corresponding to 4f7-4f65d transition of Eu2+ cover the spectral range of 370–470 nm, well matching UV and/or blue LEDs. The shortening of fluorescent lifetimes of Eu2+ followed by simultaneous increase of fluorescent intensity of Mn2+ with increasing Mn2+ concentrations is studied based on energy transfer. Upon blue light excitation the present phosphor can emit intense green/yellow in comparison with other chlorosilicate phosphors such as Eu2+ and Mn2+ co-doped Ca8Mg(SiO4)4Cl2 and Ca3SiO4Cl2, demonstrating a potential application in phosphor converted white LEDs.Highlights► Eu2+ and Mn2+ co-doped Ca8Zn(SiO4)4Cl2 phosphors were synthesized by high temperature solid state reaction. ► Their luminescence properties and energy transfer mechanism have been investigated. ► Upon blue light excitation, the present phosphor can emit intense green/yellow in comparison with other chlorosilicate phosphors. ► Results demonstrate that Ca8Zn(SiO4)4Cl2:Eu2+, Mn2+ could be a potential application on phosphor converted white LEDs.
Co-reporter:Wei Lü, Zhendong Hao, Xia Zhang, Xiaojun Wang, Jiahua Zhang
Optical Materials 2011 Volume 34(Issue 1) pp:261-264
Publication Date(Web):November 2011
DOI:10.1016/j.optmat.2011.08.026
Green-emitting phosphor Ca8Zn(SiO4)4Cl2:Eu2+ has been prepared by the solid state reaction method and there luminescence properties are investigated. The excitation spectrum of Ca8Zn(SiO4)4Cl2:Eu2+ shows an intense excitation band in the blue centered at 450 nm and emits with a maximum at 505 nm. The concentration quenching mechanism is studied and verified to be the energy transfer among the nearest-neighbor ions. Upon 450 nm excitation, the emission intensity of Ca8Zn(SiO4)4Cl2:Eu2+ is much stronger than the green emitting Ca3SO4Cl2:Eu2+ phosphor and even higher than YAG:Ce3+. This excitation spectrum range matches UV and blue light-emitting diodes (LEDS) chips very well, suggesting Ca8Zn(SiO4)4Cl2:Eu2+ could be a promising green emitting phosphor candidate for LED devices.Highlights► Intense green-emitting Ca8Zn(SiO4)4Cl2:Eu2+ has been prepared by solid state reactions. ► Their luminescence properties is investigated. ► The mechanism of concentration quenching of Eu2+ is studied in detail. ► The comparison of Ca8Zn(SiO4)4Cl2 with well known chlorosilicate phosphors in terms of PLE and PL spectra is made. ► The green LEDs are fabricated by coating the synthesized phosphors on a UV and blue LED chip.
Co-reporter:Ye Jin, Zhendong Hao, Xia Zhang, Yongshi Luo, Xiaojun Wang, Jiahua Zhang
Optical Materials 2011 Volume 33(Issue 11) pp:1591-1594
Publication Date(Web):September 2011
DOI:10.1016/j.optmat.2011.04.009
Co-reporter:Wei Lü, Zhendong Hao, Xia Zhang, Xingyuan Liu, Xiaojun Wang, Jiahua Zhang
Optical Materials 2011 Volume 33(Issue 8) pp:1262-1265
Publication Date(Web):June 2011
DOI:10.1016/j.optmat.2011.02.025
A series of Eu2+ and Mn2+ coactivated Ca3Al2(SiO4)3−δCl4δ phosphors have been synthesized by solid state reactions and their luminescence properties have been investigated by means of powder diffuse reflection, photoluminescence excitation and emission spectra, and lifetimes. The phosphor Ca3Al2(SiO4)3−δCl4δ:Eu2+, Mn2+ exhibits two dominating bands situated at 460 and 550 nm, originate from the allowed 5d → 4f transition of the Eu2+ ion and the 4T1g(4G) → 6A1g(6S) transition of the Mn2+ ion, respectively. We have discovered that energy transfers from Eu2+ to Mn2+ by directly observing significant overlap of the excitation spectrum of Mn2+ and the emission spectrum of Eu2+ as well as the decline of lifetimes of Eu2+. By utilizing the principle of energy transfer, we have demonstrated that with appropriate tuning of activator content Ca3Al2(SiO4)3−δCl4δ:Eu2+, Mn2+ phosphors exhibit potential to act as a phosphor for near ultraviolet light-emitting diodes.Highlights► Ca3Al2(SiO4)3-δCl4δ:Eu2+, Mn2+ phosphors have been synthesized by solid state reactions. ► Their luminescence properties have been investigated. ► Energy transfer mechanism between the luminescence centers Eu2+ and Mn2+ is discussed. ► Phosphors color can be toned from blue to near-white and finally to yellow. ► Ca3Al2(SiO4)3-δCl4δ:Eu2+, Mn2+ phosphors can be a candidate to act as a phosphor for NUV-LEDs.
Co-reporter:Zhendong Hao, Jiahua Zhang, Xia Zhang, Xiaojun Wang
Optical Materials 2011 Volume 33(Issue 3) pp:355-358
Publication Date(Web):January 2011
DOI:10.1016/j.optmat.2010.09.035
We report an intense full-color emission originating from 5D0,1,2,3 to 7F0,1,2,3,4 transitions of Eu3+ in CaSc2O4 upon 395 nm excitation. The emission spectra vary with increasing Eu3+ concentration, demonstrating tunable color coordinates from white to red region in the CIE chromaticity diagram. Considering the relaxation from 5DJ to 5DJ−1 through cross energy transfer, the Eu3+ concentration dependent emission spectra are well simulated based on the analysis of steady state rate equations and the measured lifetimes of the 5DJ levels. It is suggested that CaSc2O4:Eu3+ could be a potential single-phased full-color emitting phosphor for near-ultraviolet InGaN chip pumped white light emitting diodes.
Co-reporter:Meiyuan Wang, Xia Zhang, Zhendong Hao, Xinguang Ren, Yongshi Luo, Xiaojun Wang, Jiahua Zhang
Optical Materials 2010 Volume 32(Issue 9) pp:1042-1045
Publication Date(Web):July 2010
DOI:10.1016/j.optmat.2010.02.027
A bluish-green color long-lasting phosphorescent phosphor of N contained Ba2SiO4:Eu2+ for X-ray and cathode ray tubes are prepared with the chemical component formula Ba2SiO4:0.01Eu2+ − xSi3N4 − 2BaCO3 (x = 0.1 to 1.0) by the conventional high-temperature solid-state method. The phosphorescence and fluorescence properties as a function of Si3N4 content and temperature are investigated. The emission spectra show a single broad band peaking at 505 nm, which are ascribed to the 4f65d1 → 4f7 transition of Eu2+. Thermoluminescence (TL) glow-curves show that Ba2SiO4:0.01Eu2+ without N holds a high-temperature peak at 417 K. With increasing the content of Si3N4, the phosphorescence grows super-linearly and some new TL peaks appear at low temperatures of about 400, 355, 365, and 335 K. These peaks are ascribed to the formation of new traps related to N substitution for O.
Co-reporter:Yanping Li, Jiahua Zhang, Xia Zhang, Yongshi Luo, Shaozhe Lu, Xinguang Ren, Xiaojun Wang, Lingdong Sun and Chunhua Yan
Chemistry of Materials 2009 Volume 21(Issue 3) pp:468
Publication Date(Web):January 5, 2009
DOI:10.1021/cm802015u
The calcite and vaterite type LuBO3:Eu3+ nano/microcrystals with various morphologies were synthesized by the hydrothermal (HT) approach through controlling the pH values of the precursor solutions. The calcite type LuBO3:Eu3+ shows the dominant magnetic dipole 5D0−7F1 emission due to S6 inversion symmetry of Lu. It also shows a symmetrical O−Eu charge transfer (CT) excitation band, which, however, is asymmetrical and broad in the material prepared by the solid-state (SS) reaction method. The effect of the residual OH− groups introduced in HT synthesis is discussed on O−Lu exciton annihilation and local environment distortion. Two different Eu3+ centers, one of which is with inversion symmetry, are observed in vaterite type LuBO3:Eu3+. The HT sample with nanostructures, such as vaterite type flowerlike LuBO3:Eu3+, demonstrates a red shift of the CT band and appearance of a long excitation tail at the long wavelength side of the CT band. XRD, selective excitation and fluorescence decay measurements indicate that the red shift is induced by an increase of crystal lattice parameters, and the excitation tail is responsible to the Eu3+ ions located at lower symmetric sites. These sites are attributed to the positions at or close to the surface of the nanostructures in the sample. As the lower symmetric sites are selectively excited, the red emission of 5D0−7F2 of Eu3+ enhanced twice relatively to the orange emission of 5D0−7F1, exhibiting superior color chromaticity in red for display application. The luminescence properties of interior Eu3+ and outside Eu3+ are studied and discussed in detail.
Co-reporter:Yanping Li, Jiahua Zhang, Xia Zhang, Yongshi Luo, Shaozhe Lu, Zhendong Hao and Xiaojun Wang
The Journal of Physical Chemistry C 2009 Volume 113(Issue 41) pp:17705-17710
Publication Date(Web):September 18, 2009
DOI:10.1021/jp906738m
Cubic Lu2O3:Eu3+ nanorods, nanosheets, and nanoparticles are synthesized by a hydrothermal approach by adjusting the pH values of the precursor solutions. The unique luminescence properties of the nanocrystals are presented by the appearances of a long tail at the long-wavelength side of the charge transfer band (CTB), a novel 7F0−5D0 broad line, and the enhanced 624 nm emission line. The observed phenomena are more obvious with decreasing sample size in the order of nanorods > nanosheets > nanoparticles. Based on the experimental results of the thermal diffusion processes of Eu3+ from the surface to the inside of Lu2O3 particles, we conclude that the unique luminescence properties of the nanocrystals originate from the surface Eu3+. By the spectral decomposition, we obtain the excitation spectra of the interior Eu3+ and the surface Eu3+ of nanocrystals. In comparison with the bulk sample, the CTB of the interior Eu3+ presents an obvious blue shift due to the size confinement effects, while that of the surface Eu3+ shows a prominent red shift due to the distorted surface environments. The shorter lifetimes of the surface Eu3+ compared to that of the interior Eu3+ further indicate the distorted local environments on the surface of the nanocrystals. The shifts and the broadening of the CTB in Eu3+-doped nanocrystals can be well understood by the interior Eu3+ and the surface Eu3+.
Co-reporter:Yanping Li, Jiahua Zhang, Xia Zhang, Yongshi Luo, Xinguang Ren, Haifeng Zhao, Xiaojun Wang, Lingdong Sun and Chunhua Yan
The Journal of Physical Chemistry C 2009 Volume 113(Issue 11) pp:4413-4418
Publication Date(Web):2017-2-22
DOI:10.1021/jp810275t
The synthesis and upconversion luminescence properties upon a 980 nm pump of cubic Lu1.88Yb0.1Er0.02O3 nanocrystals with various shapes, e.g., nanorods, nanosheets, and nanoparticles, are studied. It is observed that with decreasing size of the nanocrystals, the relative intensity of the upconverted red emission (Er3+: 4F9/2 → 4I15/2) to the green one (Er3+: (2H11/2, 4S3/2) → 4I15/2) is increased, and a three-photon process involved in the green upconversion, as described by 4F9/2 (Er) + 2F5/2 (Yb) → 2H9/2 (Er) + 2F7/2 (Yb), is synchronously enhanced. An analysis based on steady-state rate equations indicates that the results can be induced by a large 4I11/2 → 4I13/2 nonradiative relaxation rate with a small 4F9/2 → 4I9/2 nonradiative relaxation rate. The large 4I11/2 → 4I13/2 nonradiative relaxation rate is attributed to the occurrence of efficient cross energy transfer to OH− surface group due to the good energy match. As the size of the nanocrystals decreases, the relative surface area is increased, increasing the number of OH− group that can attach to the surface, therefore, enhancing the 4I11/2 → 4I13/2 nonradiative relaxation rate through cross energy transfer to OH− surface group.
Co-reporter:Xianmin Zhang, Jiahua Zhang, Ye Jin, Haifeng Zhao and Xiao-jun Wang
Crystal Growth & Design 2008 Volume 8(Issue 3) pp:779-781
Publication Date(Web):February 6, 2008
DOI:10.1021/cg701023x
CaTiO3 nanoflowers, SrTiO3 nanocubes, and BaTiO3 nanospheres have been prepared by an environmentally friendly solvothermal technique and structurally characterized by X-ray diffraction and field emission scanning electron microscopy. Red fluorescence originating from intra 4f 1D2-3H4 transition of Pr3+ is observed by doping Pr3+ ions in CaTiO3 nanoflowers. The energy transfer and red emission processes of Pr3+ in CaTiO3:Pr3+ nanoflowers are discussed.
Co-reporter:Zhendong Hao, Jiahua Zhang, Xia Zhang, Shaozhe Lu, Yongshi Luo, Xinguang Ren, Xiaojun Wang
Journal of Luminescence 2008 Volume 128(5–6) pp:941-944
Publication Date(Web):May–June 2008
DOI:10.1016/j.jlumin.2007.11.035
α- and β-Ca2P2O7: Eu2+, Mn2+ phosphors were prepared by solid-state reaction. Phase transition from tetragonal (β-phase) to monoclinic (α-phase) is performed. A strong orange emission of Mn2+ is observed in both α-and β-Ca2P2O7: Eu2+, Mn2+ upon near ultraviolet (UV) excitation through energy transfer from Eu2+ to Mn2+. The transfer efficiencies for various Mn2+ concentrations are estimated based on lifetime measurements of the fluorescence of Eu2+ in the two phases. The photoluminescence excitation spectra of α-Ca2P2O7: Eu2+, Mn2+ can cover 400 nm of the near-UV range, denoting its potential use as a phosphor with intense orange component for white light emitting diodes (LEDs).
Co-reporter:Z.G. Nie, J.H. Zhang, X. Zhang, S.Z. Lü, X.G. Ren, G.B. Zhang, X.J. Wang
Journal of Solid State Chemistry 2007 Volume 180(Issue 10) pp:2933-2941
Publication Date(Web):October 2007
DOI:10.1016/j.jssc.2007.08.024
In this report, the Cr3+ ion was chosen as a co-dopant to modify the unpractical photon cascade emission properties of Pr3+-doped CaAl12O19 phosphors, which emit one near-UV photon from the 1S0 state followed by visible photons from the 3P0 state, into phosphors that emits two visible photons through energy transfer. The photon cascade emission process via energy transfer and the transfer mechanisms were systemically investigated by luminescence spectra and dynamics using synchrotron radiation as one of the excitation sources. The internal visible quantum efficiency of CaAl12O19:Pr, Cr was estimated and compared with CaAl12O19:Pr and the drawback to obtain the visible quantum efficiency higher than unit for CaAl12O19:Pr, Cr as a practical VUV phosphor was also discussed.The Cr3+ ion was chosen as a co-dopant to modify the photon cascade emission properties of CaAl12O19: Pr via energy transfer. The cascade emission process and the energy transfer mechanisms were systemically investigated. The drawback for CaAl12O19: Pr, Cr as a practical VUV phosphor was also discussed.
Co-reporter:Dan Wu, Zhendong Hao, Xia Zhang, Guo-Hui Pan, Yongshi Luo, Ligong Zhang, Haifeng Zhao, Jiahua Zhang
Journal of Luminescence (June 2017) Volume 186() pp:
Publication Date(Web):June 2017
DOI:10.1016/j.jlumin.2017.02.002
The step energy transfers from Pr3+ 4f5d state to Ce3+ 5d state followed by energy back transfer from Ce3+ 5d state to Pr3+ 1D2 level are studied. The Ce3+→Pr3+ energy back transfer upon Pr3+ 4f5d excitation is found to be more efficient than the normal Ce3+→Pr3+ energy transfer upon Ce3+ 5d excitation. The efficient energy back transfer is attributed to preferential excitation of the Ce3+ ion with an adjacent Pr3+ surrounding in Pr3+→Ce3+ energy transfer of the first step, whereas Ce3+ is excited randomly in the normal energy transfer. The efficiencies of Ce3+→Pr3+ energy back transfer as a function of Ce3+ and Pr3+ concentration are evaluated, respectively.
Co-reporter:Dan Wu, Zhendong Hao, Wenge Xiao, Xia Zhang, Guo-Hui Pan, Liangliang Zhang, Yongshi Luo, Ligong Zhang, Haifeng Zhao, Jiahua Zhang
Journal of Alloys and Compounds (15 May 2017) Volume 704() pp:
Publication Date(Web):15 May 2017
DOI:10.1016/j.jallcom.2017.01.344
•The luminescence properties upon 980 nm excitation are studied in Lu2O3: Tm3+,Yb3+.•The energy transfer coefficient is presented as a function of dopant concentration.•The excitation diffusion dominates the energy transfer upconversion process.Emission spectra of Tm3+ and Yb3+ codoped Lu2O3 are studied as a function of the dopant concentration upon 980 nm excitation. The upconverted near infrared emission around 811 nm from Tm3+:3H4→3H6 transition is observed due to two step energy transfers from Yb3+ through Tm3+:3F4 as the intermediate level. The optimal dopants concentrations for the strongest upconversion emission are 0.1 mol% Tm3+ and 4 mol% Yb3+. The dependence of energy transfer coefficients for the two step energy transfers on Tm3+ and/or Yb3+ concentration is studied. The obtained results indicate that the excitation diffusions among Yb3+ ions and among Tm3+ ions mainly control the energy transfer rates for the optimal dopants concentrations and thus dominate the energy transfer upconversion process.
Co-reporter:Yongfu Liu, Xia Zhang, Zhendong Hao, Xiaojun Wang and Jiahua Zhang
Chemical Communications 2011 - vol. 47(Issue 38) pp:NaN10679-10679
Publication Date(Web):2011/09/02
DOI:10.1039/C1CC14324G
A tunable full-color-emitting Ca3Sc2Si3O12:Ce3+, Mn2+ (CSS:Ce3+,Mn2+) phosphor is obtained by addition of doped ions as charge compensation. White LEDs with high Ra (> 90) are achieved using the single CSS:Ce3+,Mn2+ phosphor.
Co-reporter:Jinying Yu, Zhendong Hao, Xia Zhang, Yongshi Luo and Jiahua Zhang
Chemical Communications 2011 - vol. 47(Issue 45) pp:NaN12378-12378
Publication Date(Web):2011/10/20
DOI:10.1039/C1CC15657H
Eu2+ singly and Eu2+, Mn2+ co-doped Sr2Mg3P4O15 exhibit not only the well known blue emission band of Eu2+ peaking at 448 nm but also a new band at 399 nm in violet. They are attributed to Eu2+ on different Sr2+ sites. The Eu2+ for the violet band can transfer energy to the red emitting Mn2+ more efficiently than Eu2+ for the blue band. The new Eu2+ band could enable Sr2Mg3P4O15:Mn2+, Eu2+ to be a promising phosphor for enriching the red component of white LEDs.
Co-reporter:Leyu Feng, Zhendong Hao, Xia Zhang, Liangliang Zhang, Guohui Pan, Yongshi Luo, Ligong Zhang, Haifeng Zhao and Jiahua Zhang
Dalton Transactions 2016 - vol. 45(Issue 4) pp:NaN1545-1545
Publication Date(Web):2015/12/07
DOI:10.1039/C5DT04341G
CaO:Ce3+,Mn2+ phosphors with various Mn2+ concentrations were synthesized by a solid state reaction method. Efficient energy transfer from Ce3+ to Mn2+ was observed and it allows the emission color of CaO:Ce3+,Mn2+ to be continuously tuned from yellow (contributed by Ce3+) to red (by Mn2+) with an increase in Mn2+ concentration and upon blue light excitation. The red emission becomes dominant when the Mn2+ concentration is ≥0.014 with an energy transfer efficiency higher than 87% which can reach as high as 94% for a Mn2+ concentration of only 0.02. A critical distance of 10.5 Å for the Ce3+–Mn2+ energy transfer was determined. A faster decrease of Ce3+ luminescence intensity in comparison with its lifetime was observed on increasing the Mn2+ concentration. The analysis of this feature reveals that the Ce3+ excitation energy can be completely transferred to Mn2+ if the Ce3+–Mn2+ distance is shorter than 7.6 Å. A warm white LED was fabricated through integrating an InGaN blue LED chip and a blend of two phosphors (YAG:Ce3+ yellow phosphor and CaO:0.007Ce3+,0.014Mn2+ red phosphor) into a single package, which has CIE chromaticity coordinates of (x = 0.37, y = 0.35), a correlated color temperature of 3973 K and a color rendering index of 83.1. The results indicate that CaO:Ce3+,Mn2+ may serve as a potential red phosphor for blue LED based warm white LEDs.
Co-reporter:Jun Qiao, Jiahua Zhang, Xia Zhang, Zhendong Hao, Yongfu Liu and Yongshi Luo
Dalton Transactions 2014 - vol. 43(Issue 10) pp:NaN4150-4150
Publication Date(Web):2013/11/26
DOI:10.1039/C3DT52902A
The energy transfer and luminescence properties in the Ce3+ and Pr3+ co-activated Ca3Sc2Si3O12 (CSS) silicate garnet are studied in our work. The addition of Pr3+ exhibits a red emission around 610 nm in the green phosphor CSS:Ce3+, but the amount of Pr3+ incorporated into the phosphor is very limited due to the charge mismatch when Pr3+ substitutes for Ca2+ in CSS. In order to promote Pr3+ incorporation into CSS lattices to enhance the red emission component, the addition of Mg2+ incorporated into Sc3+ site is performed to compensate the residual positive charge caused by the substitution of Pr3+ for Ca2+ in CSS. Finally, a white LED with color rendering index of 80 and correlated color temperature of 8715 K is obtained by combining the single CSS:0.05Ce3+, 0.01Pr3+, 0.3Mg2+ phosphor with a blue-emitting InGaN LED chip.
Co-reporter:Yongfu Liu, Xia Zhang, Zhendong Hao, Yongshi Luo, XiaoJun Wang and Jiahua Zhang
Journal of Materials Chemistry A 2011 - vol. 21(Issue 41) pp:NaN16384-16384
Publication Date(Web):2011/09/13
DOI:10.1039/C1JM11601K
We report luminescence properties of Ce3+ and Mn2+ co-activated Ca3Sc2Si3O12 (CSS) silicate garnets. It is observed that Mn2+ may not only occupy Ca2+ sites to generate a yellow emission (Mn2+(I)) at 574 nm but also Sc3+ sites to generate a red emission (Mn2+(II)) at 680 nm. Considerable Mn2+ substitution for Sc3+ can be performed through balancing their charge difference by introducing a trivalent rare earth ion, such as La3+ and Ce3+, to replace Ca2+. Meanwhile, remarkable energy transfer from the green emitting Ce3+ to both Mn2+(I) and Mn2+(II) can occur, making tunable color and white light emission available in CSS:Ce3+,Mn2+ upon blue excitation into Ce3+. White LEDs combined by CSS:Ce3+,Mn2+ phosphors and blue LED chips are fabricated. A CSS:0.03Ce3+,0.2Mn2+ phosphor with deficient red emission is enriched in red by increasing Ce3+ concentration to 0.1, which leads to increase of Mn2+(II) number in case of charge compensation by more Ce3+ ions. Consequently, the color rendering index of the white LEDs is improved from 64 to 76. The results of this work indicate that CSS:Ce3+,Mn2+ garnet could be a promising single phase phosphor for white LEDs.
Co-reporter:Guotao Xiang, Jiahua Zhang, Zhendong Hao, Xia Zhang, Guohui Pan, Yongshi Luo, Shaozhe Lü and Haifeng Zhao
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 20) pp:NaN9293-9293
Publication Date(Web):2014/04/03
DOI:10.1039/C4CP01184H
The Pr3+ and Yb3+ codoped β-NaLuF4 hexagonal nanoplates with a size of 250 nm × 110 nm were synthesized by a solvothermal process. X-Ray diffraction and scanning electron microscopy were used to characterize the crystal structure and morphology of the materials. The visible and near infrared spectra as well as the decay curves of Pr3+:3P0 level were used to demonstrate the energy transfer from Pr3+ ions to Yb3+ ions. The downconversion phenomenon has been observed under the direct excitation of the 3P2 level of Pr3+. According to the analysis of the dependence of the initial transfer rate upon Yb3+ ion concentration, it indicates that the ET from Pr3+ ions to Yb3+ ions is only by a two-step ET process when the Yb3+ concentration is very low; however, with the increase of the Yb3+ concentration, a cooperative ET process occurs and gradually increases; when the Yb3+ ion concentration increases to 20 mol%, the ET from Pr3+ ions to Yb3+ ions occurs only by the cooperative ET process. When the doping concentration of Yb3+ ions reaches 20 mol% at a fixed concentration of Pr3+ ions (1 mol%), the theoretical quantum efficiency is 192.2%, close to the limit of 200%. The current research has great potential in improving the conversion efficiency of silicon solar cells.
Co-reporter:Yongfu Liu, Xia Zhang, Zhendong Hao, Xiaojun Wang and Jiahua Zhang
Journal of Materials Chemistry A 2011 - vol. 21(Issue 17) pp:NaN6358-6358
Publication Date(Web):2011/03/22
DOI:10.1039/C0JM04404K
Adding Si3N4 into green emitting Ca3Sc2Si3O12:Ce3+ garnet phosphor generates an additionally red emission band peaking around 610 nm that are assigned to Ce3+ ions having N3− in their local coordination. The excitation spectrum of the red band consists of not only a distinct band at 510 nm of itself but also an intense blue band at 450 nm that belongs to the typical Ce3+ ions with green emission, indicating a notable energy transfer from the green emitting Ce3+ ions to the red ones. The energy transfer significantly enables the achievement of a broad emission spectrum covering a red and green spectral region suitable for generating white light upon a blue light-emitting diode (LED) excitation. The decay patterns of the red and green fluorescence are discussed in relation to the effect of energy transfer. A white LED with high color rendering of 86 and low correlated color temperature of 4700 K is fabricated using the present single garnet phosphor.
Co-reporter:Yanping Li, Jiahua Zhang, Yongshi Luo, Xia Zhang, Zhendong Hao and Xiaojun Wang
Journal of Materials Chemistry A 2011 - vol. 21(Issue 9) pp:NaN2900-2900
Publication Date(Web):2011/01/10
DOI:10.1039/C0JM03394D
We synthesized a series of Yb3+, Er3+ and Tm3+ tri-doped Lu2O3 nanocrystals with various dopant concentrations by the hydrothermal approach. Due to a unique electronic state at the top of the valence band, Lu2O3 based materials exhibit intense upconversion luminescence involving 1G4 → 3H6 of Tm3+ in blue, (2H11/2, 4S3/2) → 4I15/2 in green and 4F9/2 → 4I15/2 in red of Er3+ upon near infrared excitation at 980 nm. The variation of upconversion spectra and color points with dopant concentrations and pump densities are studied in detail on the basis of energy transfer processes. An ideal white upconversion light with color coordinates of (0.327, 0.339) is obtained by controlling the intensity of red, green, and blue emission in Lu1.906Yb0.08Er0.008Tm0.006O3nanocrystals under a pump density of 8 W cm−2. Based on the present experimental data, we may predict the dopant concentrations and pump densities for any color point within or around the white light region in the tri-doped Lu2O3 nanocrystals.
