The crystalline fraction were adjusted MgO concentration and the corresponding effect on upconversion (UC) luminescence in Er3+/Yb3+ co-doped NaYF4 oxyfluorode glass-ceramics was investigated. With increase of MgO and the content of Na2O reduced, the internal network structure of the glass became compact, which made the size of NaYF4 nanocrystals unchanged, while the average distance between the nanocrystals increased significantly. Crystal growth is limited with the glass network, keeping the crystal size not changed. SNM-1 glass ceramics samples show a predominant red up-conversion emission under near infrared excitation at 980 nm, while a predominant green emission is observed in the SNM-3 samples. In this paper, it was indicated that it changed the effect of glass network modifier MgO in the glass structure. The possible mechanism responsible for the color variation of UC in Er3+/Yb3+ co-doped was discussed.

•Na(Gdx,Y1−x)F4 solid-solution nanocrystals were precipitated in glass ceramics.•The atomic radius of Er is closer to Gd than Y through our study.•The luminescence of Er3+ in glass and glass ceramics is opposite.•We research the luminescence of Er3+ in two different theory.Na(Gdx,Y1−x)F4 (x = 0, 0.3, 0.5, 0.7 and 1) solid-solution nanocrystals precipitated from glasses were prepared for the first time by conventional melting-quenching technique and subsequent heat treatment. Using Er3+ as a structural probe, the partition of lanthanide activators into the Na(Gdx,Y1−x)F4 lattice was evidenced. The types and distribution of crystallite were determined by XRD, TEM. We also studied the upconversion luminescence property of Er3+ in Na(Gdx,Y1−x)F4. The atomic radius plays an important role in luminescence properties of substitution solid solubility. The atomic radius of Er is more closer to Gd compared with Y through our theoretical calculation, which resulted that Er ions replace Gd ions from NaGdF4 is easier than Er ions replaced Y from NaYF4. Therefore, the intensity of emission can be enhanced significantly when the precipitation crystal from NaYF4 turn into NaGdF4.(a) Upconversion luminescence of Er3+ ions in glass ceramic with different radio of YF3 and GdF3 under 980 nm laser diode excitation; (b) crystal structure diagram of Na(Gdx,Y1−x)F4.

A novel white-emitting Ca2Ga2GeO7:Dy3+ phosphor was synthesized via a high-temperature solid-state reaction. The crystal phase was analyzed by X-ray diffraction (XRD), and the photoluminescence (PL) properties were studied by luminescence spectra and fluorescence decay curves. Under the excitation of 347 nm, the obtained phosphor exhibited strong emission in the blue region peaked at 478 nm, yellow at 574 nm and a weak red emission band at 665 nm, corresponding to the characteristic transitions of 4F9/2 to 6H15/2,6H13/2 and 6H11/2 of Dy3+, respectively. By varying the doping concentration of Dy3+, tunable colors from blue-white to yellow-white were obtained in the phosphors. Besides, by codoping charge compensators (Li+, Na+, K+ and Ga3+) in Ca2Ga2GeO7:Dy3+, the optimum CIE color coordinate and PL intensity were obtained in Ca2Ga2GeO7:Dy3+,K+. Accordingly, the PL mechanism of Ca2Ga2GeO7:Dy3+ was discussed briefly.PL spectra of Ca2-xGa2GeO7:xDy3+ (a) and CIE chromaticity diagram for Ca2-xGa2GeO7:xDy3+ (λex=347 nm) (b)Download high-res image (80KB)Download full-size image

•Effect of heat treatment mechanism on NaYF4 oxyfluoride glass-ceramics.•The two-step heating process obtain the different size nanocrystals in the same piece of glass.•The UC luminescence intensity and color variation can be adjusted by heat treatment mechanism.Effect of glass heat treatment technology on upconversion (UC) luminescence in Er3+/Yb3+ co-doped NaYF4 oxyfluorode glass-ceramics (GC) was investigated. First, NaYF4 nanocrystals were precipitated from single process glasses after heat-treatment of different temperature, and the nanocrystals size of NaYF4 in the heat-treat temperature of 540 °C and 590 °C samples, the crystal size is 5 nm and 27 nm, respectively. Moreover, the two-step heating process obtain the different size nanocrystals (5 nm and 28 nm) in the same piece of glass. It is found that the UC luminescence properties of Er3+ ions were changed in accordance with the heat treatment mechanism, and the Er3+ concentration of nanocrystals. Compare with single process, the UC luminescence properties of two-step heat treatment of enhancement of green emission intensity and fluorescence strength.Download high-res image (493KB)Download full-size image

Comprehensive investigations of near infrared (NIR) downshift and visible upconversion luminescence (UCL) mechanisms were carried out for Yb3+ single-doped and Er3+,Yb3+ co-doped SiO2 inverse opals under excitation at 256, 378, 520 and 980 nm. NIR emission at 976 nm from the Yb3+–O2− charge transfer state and UCL emission at 500 nm due to the cooperative emission of two Yb3+ ions were observed in SiO2:Yb3+ inverse opal upon excitation at 256 and 980 nm, respectively. The cooperative UCL of two Yb3+ ions was suppressed due to the photon trap created by the photonic band gap. For the SiO2:Er3+,Yb3+ inverse opals, NIR emission of Yb3+ at 976 nm and of Er3+ at 1534 nm were observed upon excitation at 256, 378 and 520 nm, respectively. Upon excitation at 378 and 520 nm, the 976 nm NIR emission of Yb3+ does not arise from (2H11/2/4S3/2) + 2Yb3+(2F7/2) → Er3+(4I15/2) + 2Yb3+(2F5/2) traditional quantum cutting. The NIR emission of Yb3+ at 976 nm may be due to the Er3+(2H11/2) + Yb3+(2F7/2) → Yb3+(2F5/2) + Er3+(4I11/2) cross-relaxation energy transfer process upon excitation at 520 nm. The NIR emission of Yb3+ at 976 nm may arise from the cross-relaxation energy transfer of Er3+(4G11/2) + Yb3+(2F7/2) → Yb3+(2F5/2) + Er3+(4F9/2) and Er3+(4F9/2) + Yb3+(2F7/2) → Yb3+(2F5/2) + Er3+(4I13/2) upon excitation at 378 nm.

•The Li+ codoping on the vision emission in Tb3+–Yb3+ co-doped transparent glass-ceramics.•We proved that the Li+ diffuse to various interstitial sites in the NaYF4 lattice.•The effect the Li+ codoping in Eu3+ ions prove that change the symmetry of the lattice.•The mechanism responsible for the enhancement of Li+ enhancement reason were discussed.The glass ceramics samples with composition of 40SiO2–25Al2O3–18Na2CO3–10YF3–7NaF–0.5TbF3–1YbF3–xLi2CO3 (in mol%, x = 0, 1, 2, 3, 4, 5 and 6) were prepared using the conventional quenching techniques. The effect of the Li+ codoping on the enhancement upconversion (UC) and Stokes emission in Tb–Yb co-doped transparent glass-ceramics were investigated. Compared with the glass-ceramics sample without Li+ codoping, the UC and Stokes emission intensity of glass-ceramics samples with Li+ codoping were increased. Particularly, the green UC emission intensity band centered at 543 nm was strongly increased twice with the increase of Li+ up tp 4 mol%. Therefore, the Stokes emission results showed that the incorporation of Li+ ions into the NaYF4:Eu3+ lattice could induce a remarkable change of the Stokes emission intensity in red region (R = IED/IMD) with 393 nm excitation wavelength. It was indicated that it improved the effect of Li+ codoping in Tb–Yb on symmetry of the lattice. The possible mechanism responsible for the enhancement of UC and Stokes emission in Tb3+-Yb3+ co-doped were discussed.

Cubic-to-hexagonal phase transformation and enhancement of upconversion emission are simultaneously achieved by modifying the ratio of ZnO/Na2O content in the Tb3+-Yb3+ co-doped oxyflouride Zincatesilion glass ceramics containing NaYF4 nanocrystals. XRD and TEM data have revealed that the crystallization of NaYF4 from α phase to β phase. Additionally, upconversion emissions were obtained from these Tb3+-Yb3+ glass ceramics under 980 nm excitation. Compared with the cubic α-NaYF4 nanocrystals of glass ceramics, the upconversion intensity augmented drastically owing to the phase transformation that the NaYF4 has changed from α into β. Therefore, the PL results showed that the cubic-to-hexagonal the NaYF4:Eu3+ lattice could induce a remarkable change of the PL intensity in red region (R = IED/IMD) with 393 nm excitation wavelength. It was indicated that it changed the phase transformation in Tb-Yb on symmetry of the lattice.

NaAlSiO4: Tb3+, Bi3+ phosphor was synthesized with green LPL and PSL observed.The influence of metal ion Bi3+ on the optical storage properties of NaAlSiO4: Tb3+ was investigated in detail, which help us to further understand the mechanism of the energy storing and its subsequent releasing in optical storage materials.Owing to the existence of deep and stable trap TB, green PSL can still be observed after 72 h since the excitation was stopped.All the results indicate that this phosphor has potential applications as an optical storage material.NaAlSiO4: Tb3+, Bi3+ phosphor was synthesized with green long persistent luminescence (LPL) and photo-stimulated luminescence (PSL) observed. The influence of metal ion Bi3+ on the optical storage properties of NaAlSiO4: Tb3+ was investigated in detail. The emitter Tb3+ introduced two kinds of traps located at 350 K (TA) and 440 K (TB) in the thermoluminescence (TL) glow curve. Bi3+ as a codopant ion introduced a new trap peaking at 390 K (TC), which contributed to the improved LPL properties. Besides, owing to the existence of deep and stable trap TB, green PSL can still be observed after 72 h since the excitation was stopped. Accordingly, the mechanism of LPL and PSL process was discussed briefly.

A series of Ba5Si8O21:0.02Eu2+,0.09RE3+ persistent phosphors were synthesized by the solid-state reaction method. The measurement results of photoluminescence (PL), phosphorescence and thermoluminescence (TL) were analysed and discussed. The XRD results showed that samples codoped with different RE3+ were Ba5Si8O21 single pure phase. Under the excitation, all samples exhibited a broad Eu2+ characteristic emission, and the La3+ co-doped sample emitted the brightest photoluminescence even though its persistent luminescence property was the worst because of the weakest electronegativity. However, Nd3+ electronegativity was suitable, thus after activation, the Ba5Si8O21:Eu2+,Nd3+ sample had the best persistent luminescence performance with the highest phosphorescence intensity and the persistent luminescence decay time beyond 8 h. The Nd3+ co-doped sample also had the largest thermoluminescence integral area which proved effectively it had longer persistent luminescence time. The luminescence mechanism was also proposed to study the photoluminescence and persistent luminescence process. These results showed that RE3+ electronegativities were distinctly important for persistent phosphors and choosing suitable electronegativity codopant was conducive to enhancing the phosphorescent performance.Persistent luminescence decay curves of Ba5Si8O21:Eu2+, RE3+ (a) and persistent luminescence images of Ba5Si8O21:Eu2+, Nd3+/La3+phosphors (b)

•Yb3+, Tb3+ co-doped YPO4 inverse opal photonic crystal was prepared.•Quantum cutting emission of Tb3+, Yb3+ was investigated in photonic crystals.•Tb3+-Yb3+ quantum cutting quantum efficiency could be enhanced by inhibited of the Tb3+ spontaneous emission.Yb3+, Tb3+ co-doped YPO4 inverse opal photonic crystal was prepared directly by sol–gel technique in combination with self-assembly method. With the influence of the photonic band gap, quantum cutting emission of Tb3+, Yb3+ was investigated in photonic crystals by photoluminescence and fluorescence lifetime. The result clearly shows that, when the spontaneous emission of donor Tb3+ is inhibited by photonic band gap, Tb3+-Yb3+ quantum cutting quantum efficiency from Tb3+ to Yb3+ could be enhanced from 131.2% to 140.5%. The mechanisms for the influence of the photonic band gap on quantum cutting process of Tb3+ and Yb3+ are discussed. We believe that the present work will be valuable for the foundational study of quantum cutting energy transfer process and application of quantum cutting optical devices in spectral modification materials for silicon solar cells.

The upconversion (UC) of the rare earth doped glass-ceramics has been extensively investigated due to their potential applications in many fields, such as color display, high density memories, optical data storage, sensor and energy solar cell, etc. Many series of them, especially the oxyfluorides glasses containing Ba2LaF7 nanocrystals were studied in this review work, due to the thermal and mechanical toughness, high optical transmittance from the ultraviolet to the infrared regions, and a low nonlinear refractive index compared to the other commercial laser glasses. Moreover, the energy transfer (ET) between the rare earth ions and transition metals plays an important role in the upconversion process. The cooperative ET has been researched very activly in UC glasses due to applications in the fields of solar cells, such as in the Er/Yb, Tm/Yb, Tb/Yb, Tb/Er/Yb and Tm/Er/Yb couples. The present article reviews on the recent progress made on: (i) upconversion materials with fluoride microcrystals in glasses and the mechanisms involved, including the UC in double and tri-dopant RE ions activated fluoride microcrystal, energy transfer process; and (ii) the effect of the metal Mn and nanoparticles of Au, Ag, Cu on the enhancement of UC emissions. Discussions have also been made on materials, material synthesis, the structural and emission properties of glass-ceramics. Additionally, the conversion efficiency is still a challenge for the spectra conversion materials and application; challenge and future advances have also been demonstrated.Mechanism for the UC and NIR of the Er3+/Yb3+ co-doped SAB glass-ceramics[136]

Visible-light persistent phosphors are commonly used as self-sustained night vision and fluorescence labeling materials. From the inspiration of the structure of six-membered rings plane in Ba4(Si3O8)2, a similar structure of Ba5Si8O21 is expected that could exhibit more excellent phosphorescence property. In this Article, we report a novel visible long-lasting luminescence phosphor of Eu2+/Dy3+ codoped Ba5Si8O21 for the first time. Ba5Si8O21:Eu2+,Dy3+ phosphor could be activated effectively by sunlight or even in severe weather conditions, which is mainly attributed to the broad excitation spectrum (200–455 nm) and highly responds to UV-A and violet-light in the solar spectrum. After activation, Ba5Si8O21:Eu2+,Dy3+ emits intense emission at 380–680 nm with persistent phosphorescence beyond 16 h. Moreover, it exhibits excellent and stable phosphorescence even in water, indicating that Ba5Si8O21:Eu2+,Dy3+ will be a all-weather material that can be effectively and repeatedly charged by natural daylight in all kinds of open-air environments. Furthermore, the quantum tunneling behavior was illustrated in the afterglow mechanism.

Up-conversion (UC) crystals of lanthanide-doped LuF3 with different morphologies (nanoparticles, shuttle- and litchi-like microcrystals) have been synthesized via a facile ionothermal method. The dependence of the morphological differences of the products on the solvent composition and reaction time has been studied in detail, and a possible formation mechanism has also been proposed. The emission spectra showed that the UC luminescence intensity can be adjusted by changing the morphology of LuF3. Both LuF3:Yb3+/Er3+ and LuF3:Yb3+/Ho3+ nanoparticles synthesized using water/IL (ionic liquid) as mixed solvent exhibit a significant enhancement of the yellowish-green emission under 980 nm laser excitation. Besides, nearly NIR (near-infrared) to NIR UC luminescence has been achieved in LuF3:Yb3+/Tm3+ nanoparticles synthesized using EG (ethylene glycol)/IL as mixed solvent. Furthermore, the ratio of the emission intensity at 812 nm to that at 545 nm reaches 55. Our results indicate that lanthanide-doped LuF3 provides promising applications in chromatic displays and bio-imaging.

•Luminescence in Eu/Tb codoped glass and transparent glass–ceramics were study.•The color-tunable emission luminescence in the glasses by changing Eu3+/Tb3+ ratio.•The color changed in glass–ceramics by varying Eu3+/Tb3+ coordination environment.•The transparent nanocomposite could be potentially applicable in color displays.The β-PbF2 nanocrystals containing SiO2–AlF3–BaF2–PbF2–GdF3 transparent glass–ceramics were fabricated by high temperature melting–quenched technique, and their luminescence properties were investigated. Transparent glass–ceramics were obtained after heat treatment at their first crystallization temperature. Compared with the glass samples before heat treatment, high efficiency luminescence of Eu3+/Tb3+ co-doped was observed in the glass–ceramics under excitation 377 nm, and the emission intensity of Eu3+-doped showed different tendency to that emission intensity of Tb3+-doped after nanocrystals precipitate, resulting in color tunable luminescence. In addition, the energy transfer between the Eu3+ and Tb3+ ions are also investigated. The results suggest that the Eu3+/Tb3+ co-doped transparent glass–ceramics could be potentially applicable in the solid-state color displays.

The transparent glass–ceramics SiO2–AlF3–BaF2–TiO2–CaCO3 containing BaF2 nanocrystals were successfully prepared by the conventional melting method. The effect of the AuNPs on the enhancement upconversion and near-infrared emission in Er3+/Yb3+ co-doped transparent glass–ceramics under 980 nm laser diode excitation were investigated. The transmission electron microscopy (TEM) micrograph showed the average diameter size of gold nanoparticles is estimated about 4–6 nm. Compared with the glass–ceramics sample without HAuCl4, the upconversion and near-infrared emissions intensity of SAB glass–ceramics samples with HAuCl4 were significantly increased. Particularly, the red UC emission intensity band centered at 850 nm strongly increased about twenty-fold with the increase of HAuCl4 concentration and reaches its maximum at 1.5 mol%, then decreases due to the self-quenching effect. The possible mechanism responsible for the enhancement of upconversion and near-infrared emission in Er3+/Yb3+ co-doped due to effectiveness of surface plasmon resonance were discussed.

The highest quantum efficiency among amorphous materials was recently observed in the ns2-type Sn2+ activators doped ZnO–P2O5 glass system, which is comparable to the MgWO4 crystal. In this paper, Mn2+/Sn2+-codoped low-melting 44P2O5–36ZnO–20Li2O (PZL) glasses were prepared by the melt-quenching method to explore blue and red emission materials for greenhouse. Photoluminescence properties of the PZL glasses were investigated systematically by decay curves and absorption, excitation, and emission spectra. The glasses have high optical transparency in the visible region, and can emit intense red light excited at 300, 354, 409, and 505 nm. Significantly, upon 300 nm excitation, dual blue/red emissions were achieved. Moreover, the ratio of red to blue light could be tuned by adjusting the energy-transfer (ET) of Sn2+→Mn2+ through simply adjusting the content of Mn2+. Our research extends the utilization of solar energy in glass greenhouse for plant cultivation.

•A significant enhancement of LLL property is achieved by doping Dy3 + ions.•Afterglow of Li2Sr0.993SiO4:0.003Eu2 +, 0.004Dy3 + can persist over 15 h.•Vo.. as electron traps is responsible for LLL of single/co-doped samples.A novel orange-yellow long-lasting phosphor (LLP) Li2SrSiO4:Eu2 +, Dy3 + was developed. The incorporation of the orbitals of Dy3 + in the formation of the discrete level associated with oxygen vacancy (Vo..) causes a change in the number of traps, which largely extends the thermoluminescence characteristics and evidently improves the long persistent luminescence property of the phosphor. Both fluorescence and phosphorescence spectra of Li2SrSiO4:Eu2 +, Dy3 + reveal broad and intensive emission extending from 500 to 700 nm with a peak at about 567 nm, this indicates that photoluminescence(PL) and long-lasting luminescence (LLL) are from the same Eu2 + ions center. After the removal of UV light, the afterglow of the sample with the optimum doping concentration can persist over 15 h above the recognizable intensity level (≥ 0.32 mcd/m2).

•CuNPs and BaF2 nanocrystals precipitated in SiO2–AlF3–BaF2–TiO2–CaCO3 glass–ceramics.•Effect of CuNPs on the enhancement UC emission intensity of Tb–Yb were investigated.•Energy transfer process between Cu+ and Tb3+ ions was demonstrated by decay times.The transparent glass–ceramics SiO2–AlF3–BaF2–TiO2–CaCO3 containing BaF2 nanocrystals were successfully prepared by conventional melting method. The effect of CuNPs on the enhancement upconversion emission intensity in the Tb3+/Yb3+ co-doped transparent glass–ceramics under 980 nm laser diode excitation were investigated. The structural investigation carried out by X-ray diffraction (XRD) and transmission electron microscopy (TEM) evidenced the formation of cubic BaF2 nanocrystals. The distribution of Copper nanoparticles and the average diameter size which were confirmed by the results of XRD, TEM measurements. Compared with the glass–ceramics sample without Cu2O element, the intensity of upconversion emission was significantly increased. Particularly, the red UC emission intensity bands at 588 and 624 nm strongly increased with the increase of Cu2O concentration and reached its maximum at 2.5 mol.%, then decreases due to the self-quenching effect. The possible mechanism responsible for the enhancement of upconversion emission intensity in the Tb3+/Yb3+ co-doped due to effectiveness of surface plasmon resonance was discussed.UC emission spectra and CIE1931 chromaticity coordinates of SAB–0Cu, SAB–1.0Cu, SAB–1.5Cu, SAB–2.0Cu, SAB–2.5Cu and SAB–3.0Cu glass–ceramics samples under 980 nm LD excitation.

•Cu+ cations were introduced into amorphous glasses via Cu+–Na+ ion-exchange technique.•Energy-transfer of Cu+ → Tb3 + was systematically investigated.•Enhancement of Tb3 + emissions was achieved in Cu+–Na+ ion-exchanged glasses.Cu+ cations were introduced into the sodium-borosilicate (SBS) glasses via a Cu+–Na+ ion-exchanged technique. The photoluminescence (PL) properties of Cu+, Tb3 + single- and co-activated SBS glasses, and the energy transfer (ET) process from Cu+ to Tb3 + cations were systematically investigated through energy-level diagram, decay curves, absorption spectra, PL excitation and emission spectra. Under the excitation of UV-light, Cu+-activated SBS glasses emit blue-greenish photons in the visible range, originating from the 3d94s1 → 3d10 transition of Cu+ cations. Moreover, the intensities of the excitation and emission bands of Cu+ can be tailored by appropriately tuning the ion-exchange time. Significantly, enhancement of green emission of Tb3 + was observed via utilization of Cu+ cations as efficient sensitizers. The influence of the ion-exchange temperature and the salt bath with varied ratios of CuSO4 to Na2SO4 on the interaction between Cu+ and Tb3 + cations was also discussed. Our research will help understand the enhancement mechanisms of Tb3 + emissions in Cu+/Tb3 +-codoped amorphous systems.

•The Cu ions were introduced into glasses by the Cu+ for Na+ ion exchange method.•Different valence states of Cu, namely, Cu0, Cu+, and Cu2 +, were incorporated into glass.•Some Bi near infrared active centers formed during the ion exchange process.•Some lower valence states of Bi were oxidized in the heat treatment procedure.The copper (Cu) atoms were incorporated into the bismuth (Bi) doped silicate glasses by the copper for sodium (Cu–Na) ion exchange method. After the ion exchange process, the Cu ions were introduced into the glass matrix with different copper valence states, namely, Cu0, Cu+, and Cu2 +. Bi3 + ions could be reduced to lower valence states of Bi containing Bi near infrared (NIR) active centers with the incorporation of the Cu ions, resulting in the enhancement of the Bi NIR luminescence intensity. During the heat treatment process, some lower valence states of Bi containing Bi NIR active centers could be oxidized, resulting in the attenuation of the NIR luminescence of Bi. Our research may extend the understanding of chemical environment modulation in Bi valence states and offer a valuable way to enhance the NIR luminescence intensity of Bi in glasses.

•NIR emission of Er–Nd has significantly enhanced after heat treatment changing times.•Broadband NIR of Er–Nd with an FWHM extending from 1250 to 1700 nm could be 340 nm.•NIR emission of Er–Nd, which covered the whole O, E, S, C, L and U bands was observed.•NIR emission bands at 1065 and 1546 nm are best for Nd/Er ratio of 2.5.•Energy transfer processes between the Nd3 + and Er3 + ions were also discussed.The optimizing Nd/Er ratio for enhancement of broadband near-infrared (NIR) emissions in the Er3 +–Nd3 + co-doped SiO2–AlF3–BaF2–TiO2–CaCO3 (SABTC) transparent silicate glass-ceramics containing BaF2 nanocrystals under 808 nm excitation was investigated. The broadband NIR emission bands from 850 to 1700 nm, which covered the whole O, E, S, C, L and U bands were observed in the Er3 +–Nd3 + co-doped glass-ceramics samples, as a result of the overlap of Nd3 +-doped emission band centered at 1342 nm and the emission from 4I13/2 → 4I15/2 transition of Er3 + band centered at 1546 nm. The NIR emission intensity of Er3 +–Nd3 + co-doped bands centered at 895, 1065, 1342 and 1546 nm, becomes stronger with varied depending on the mixing ratio of Nd3 + and Er3 + ions, and the full width at half-maximum (FWHM) extending from 1250 to 1700 nm could be 340 nm. Most NIR emission bands at 1065 and 1546 nm are observed for the SABTC-1.0N0.4E glass-ceramics sample, corresponding to Nd/Er ratio of 2.5. At the same time, the energy transfer processes between the Nd3 + and Er3 + ions were also discussed.

The effect of glass network modifier R2O (R=Li, Na, K) on upconversion luminescence in Er3+/Yb3+ co-doped NaYF4 oxyfluoride glass-ceramics was investigated. NaYF4 nanocrystals with different sizes were studied under glass network modifier alkali mental oxide. The nanocrystals size in NaYF4 of Li2O modified samples was 11 nm, whereas in the Na2O and K2O modified sample, the crystal size was 25 and 43 nm, respectively. It was found that red, yellow and green upconversions were observed in SAL, SAN, SAK glass ceramics. The reported results would deepen the understanding of size effects on the lanthanide upconversion in nanocrystals.TEM micrographs of nanocrystals synthesized at different alkali metal oxides (a) SAL, (b) SAN; (c) SAK; (d–f) EDS spectra with increase of grain size

•The Ag ions were introduced into glasses by Ag+ for Na+ ion exchange method.•The Ag ions were mainly in the ionic form within the glasses after ion exchange.•The Ag nanoparticles formed after heat treatment.•The Ag incorporation causes effective enhancement of Bi near-infrared emission.The Ag ions were introduced into the Bi doped silicogermanate glasses by Ag+ for Na+ ion exchange method. After ion exchange, the X-ray photoelectron spectroscopy (XPS) spectrum implied the Ag ions were mainly in ionic form (Ag+) within the glasses. With the increase of the Ag+ concentration, more relaxation of local structure would be induced at the non-bridging oxygen (NBO), meaning that the network gave more negative sites. Bi3+ ions could be reduced to lower valence states of Bi containing Bi near infrared (NIR) active centers with the depolymerization of glass network, resulting in the enhancement of the Bi NIR luminescence. After heat treatment, the XPS, absorption spectra and transmission electron microscope (TEM) images revealed Ag nanoparticles (Ag NPs) formed in glasses. With the increase of the Ag NPs concentration, more NBOs released from Ag+, which led to reduce more Bi3+ ions to lower valence states of Bi containing Bi NIR active centers, resulting in further enhancement of the NIR luminescence. Our research may extend the understanding of structural modulation in Bi valence states and offer a valuable way to enhance the NIR luminescence of Bi in glasses.

The blue emission of Ca3SnSi2O9 was identified to arise from the recombination of electrons and holes via intrinsic oxygen vacancy defects using photoluminescence spectra measurements, density functional theory calculations, and thermoluminescence analysis. A significant enhancement in the photoluminescence intensity of the blue emission was observed in samples of Ca3SnSi2O9 co-doped with fluorine, which was attributed to the increased number of oxygen vacancy defects produced in Ca3SnSi2O9. Most importantly, the improvement of the photoluminescence intensity of Dy3+ demonstrated that energy transfer from the Ca3SnSi2O9 host to the activators became more effective when fluorine was co-doped. It indicates that fluorine could be introduced into the Ca3SnSi2O9 host by this approach, which produced more oxygen vacancies and contributed to the improved photoluminescence performance of the activators.

•Both the emission intensity of Eu3+ and Dy3+ were enhanced by codoping with Bi3+.•Energy transfer from Bi3+ to Dy3+ and Eu3+ was investigated in Ca3SnSi2O9.•A tunable color emission could be realized in Ca3SnSi2O9: Bi3+, Dy3+, Eu3+.The bright blue emission at 420 nm, originating from the charge transfer transition of the self-activated SnO6 octahedron, was observed in Ca3SnSi2O9 host matrix. Bi3+, Dy3+ and Eu3+ exhibited their characteristic emission under ultraviolet excitation when these activators were doped into Ca3SnSi2O9, respectively. The emission intensity located at the blue–yellow and red region of Dy3+ and Eu3+ could be further improved when Bi3+ was co-doped in Dy3+, Eu3+ doped Ca3SnSi2O9. Furthermore, a tunable color emission, especially the white light, was realized in Ca3SnSi2O9: Bi3+, Dy3+, Eu3+ phosphors by adjusting the relative concentration of the activators. It demonstrates that Bi3+, Dy3+, Eu3+ codoped Ca3SnSi2O9 could potentially be used as a tricolor phosphor for the fabrication of phosphor-converted light emitting diodes (pc-LED).

•The silver was introduced into the glasses by Ag+–Na+ ion exchange.•Energy transfer from Ag+/silver aggregates to Tb3 +.•Silver nanoparticles led to a significant enhancement in Tb3 + luminescence.Different ionic silver species and Ag nanoparticles (Ag NPs) were prepared by Ag+–Na+ ion exchange method in Tb3 +-doped sodium–aluminosilicate glasses, and the interaction between Ag species and Tb3 + ions was studied. Two excitation peaks centered at 280 nm and 375 nm which ascribed to Ag+ and Ag aggregates (Ag2+, Ag3+…) respectively were observed in as-made glasses. Owing to energy transfer (ET) from Ag+/silver aggregates to Tb3 +, significant enhancements of Tb3 + emission were observed under certain excitation. After heat treatment, the results of absorption spectrum and TEM patterns revealed that silver nanoparticles (Ag NPs) with diameter of about 5 nm were formed in glasses, and it was found that the Ag NPs led to a significant enhancement in Tb3 + luminescence under 375 nm excitation. A possible mechanism of energy transfer from Ag species to Tb3 + ions was proposed.

•The abnormal fluorescent intensity didn't obey the theory of optical basicity.•The optical basicity theory was applicable in these glasses.•The 3-membered [GeO4] rings were a benefit for the near infrared luminescence.•The interaction of optical basicity and structure led to the abnormal phenomenon.Bismuth doped calcium germanate glasses were prepared, and the relationship between Bi near-infrared (NIR) luminescence and the glass structure was investigated. The NIR emission with 808 nm excitation covered the whole optical telecommunication window. The intensity of the NIR emission increased firstly and then declined with the increasing CaO content, which cannot be explained by the theory of optical basicity. The X-ray photoelectron spectroscopy (XPS) and the visible luminescence spectra showed that the trivalent Bi3+ could reduce to lower state of Bi in these glasses. The Fourier transform infrared (FT-IR) absorption spectra and Raman spectra indicated that the major structure units were [GeO4] tetrahedral, and the 4-membered [GeO4] rings converted into 3-membered [GeO4] rings with the increasing optical basicity. The nature of NIR emission and the reason of the abnormal phenomenon were discussed.

•Ce3 + ions played a role as sensitizers in improving the luminescence of multi-activators.•Dual energy-transfer of Ce3 + → Tb3 + and Ce3 + → Mn2 + was systematically investigated.•Tunable full-color emitting was obtained in Ce3 +–Mn2 +–Tb3 + co-activated glasses.A series of trichromatic/white-emitting 15CaO–55B2O3–30SiO2 glasses co-doped with Ce3 +/Tb3 +/Mn2 + were synthesized in air by a melt-quenching method. Ce3 + ions played a role as sensitizers in improving the photoluminescence performance of multi-activators. Dual energy transfer (ET) processes of Ce3 + → Tb3 + and Ce3 + → Mn2 + were observed in Ce3 +–Mn2 +–Tb3 + co-activated glasses. The hues of the fabricated glasses covered the regions from blue, green, to orange–red, and a wide-range-tunable warm white light emission was realized by tuning the ET proportion from excitation source to the co-activated Mn2 + and Tb3 + ions through utilizing Ce3 + ions as the multi-sensitizers. It indicates that these glasses are expected to be potential phosphor candidates for deep UV-pumped white-LED.

•The Structure of Er3 +-doped germanate glasses are investigated.•Effect of phonon energy and vibrational quantum on UC and NIR emission is studied.•The effect of vibrational quantum on the UC and NIR luminescence property is primary.The structures and optical properties of GeO2–Li2O–Er2O3 glasses are investigated. The results indicate that the phonon energy of Er3 +-doped germanate glasses is decreases with the increasing in Li2O content, but the upconversion and near infrared luminescence intensity is decreases. The analysis considers that it is attributed mainly to the effect of OH− group (about 3100–3500 cm− 1) on the upconversion luminescence of Er3 + was bigger than that of the phonon energy, and also the OH− group strongly influence the NIR luminescence.

•A novel orange-yellow emitting phosphor: K3Gd(PO4)2:Tb3+, Eu3+ was prepared.•The energy transfer from Tb3+ to Eu3+ in K3Gd(PO4)2 was investigated carefully.•K3Gd(PO4)2:Tb3+, Eu3+ can realize tunable color emission from greenish to orange.A n-UV convertible phosphor K3Gd(PO4)2:Tb3+, Eu3+ with tunable-emitting color has been synthesized by the solid state reaction. Under the Tb3+ excitation (373 nm), the Eu3+ emissions increase dramatically with increasing the Eu3+ content due to the efficient energy transfer from Tb3+ to Eu3+, which has been justified through the luminescence spectra and fluorescence decay curves. K3Gd(PO4)2:0.5Tb3+, yEu3+ can achieve tunable color emissions from yellowish-green through orange-yellow and ultimately to reddish-orange by simply adjusting the Eu3+ content. In addition, the energy transfer mechanism was demonstrated to be the dipole–dipole interaction and the energy transfer efficiency was calculated. The present results indicate that this novel orange-yellow emitting phosphor can be as a potential candidate for the application in white LEDs.

•We prepared UC of Er–Tb–Yb co-doped glass-ceramics containing Ba2LaF7 nanocrystals.•The UC emission intensity in the glass-ceramics has enhanced after heat treatment.•There was possibly an energy transition process from Tb3+ to Er3+ ions.•The UC emission intensity increases and reaches its maximum at 2.5Yb3+ concentration.Transparent glass-ceramics SiO2–AlF3–BaF2–TiO2–LaF3 (SABTL) containing Ba2LaF7 nanocrystals were successfully prepared by heat treatment process through conventional melting method. The crystal size in the glass-ceramics increased gradually under the changing of heat treatment temperatures and times, which was confirmed by the results of XRD, TEM measurements. The intensity of the blue, green and red upconversion luminescence around 490 nm, 525 nm, 546 nm, 657 nm which originate from the transitions 5D4 → 7FJ (J = 6 and 5) of Tb3+ ions and (2H11/2, 4S3/2, 4F9/2) → 4I15/2 transitions of Er3+ ions, respectively, were strongly observed after heat treatment under 980 nm laser diode excitation. The intensity of upconversion luminescence was increased gradually with the increase of Yb3+ concentrations and reaches its maximum at 2.5 mol%. The upconversion luminescence and energy transfer process between Tb3+, Yb3+ and Er3+ ions in the glass-ceramics were discussed.

•A phosphor of Ba4(Si3O8)2:Eu2+,Er3+ emits high-brightness greenish-blue afterglow.•The energy transfer from Eu2+ to Er3+ was observed in the co-doped sample.•The incorporation of Er3+ ions enhances the afterglow behavior of this phosphor.•The Eu2+/Er3+ co-doped sample shows brighter and longer afterglow.A greenish-blue long-persistent luminescence (LPL) material of Ba4(Si3O8)2:Eu2+,Er3+ was synthesized by traditional solid state reaction method. Compared to Eu2+ single-doped Ba4(Si3O8)2 phosphor, the Eu2+/Er3+ co-doped sample shows brighter and longer afterglow. Photoluminescence (PL) and long-persistent luminescence (LPL) results indicated that PL and LPL are from the same luminescent centers which are ascribed to the 4f65d1 → 4f7 transition of the Eu2+. The incorporation of Er3+ ions largely extends the thermoluminescence characteristics and evidently enhances the LPL behavior of the phosphor. Since the TL glow curve in the Eu2+/Er3+ co-doped sample phosphor is different from that of Er3+ single-doped sample, it is considered that Er3+ plays an important role in LPL behavior.

A series of CaYAl3O7: Ce3+, Tb3+ phosphors has been synthesized by combustion method for the first time. XRD measurements demonstrated the phosphor hosts keep pure tetragonal crystalline structure at 850 °C. The photoluminescence properties of Tb3+, Ce3+ singly and co-doped CaYAl3O7 have been discussed. Under the Ce3+ excitation at 360 nm, enhanced green emission was obtained in Ce3+ co-doping CaYAl3O7: Tb3+ sample. And combining the photoluminescence properties and fluorescence decay curves, energy transfer from Ce3+ to Tb3+ was investigated and a possible mechanism was proposed. The results indicate that CaYAl3O7: Ce3+, Tb3+ phosphors have potential applications as a kind of near ultraviolet-convertible green phosphor for white light-emitting diodes by Ce3+ co-doped which perfectly makes excitation band of Tb3+ extend from 243 to 360 nm.

•Effects of Mn2+ on the enhancement red UC emission in Mn–Er–Yb were investigated.•The UC emission of Mn–Er–Yb was strongly enhanced after a heat treatment process.•The red UC emission of Mn–Er–Yb increases with the increase of Mn2+ concentration.•The ET Bridge was constituted by the ET process between Er3+ and Mn2+–Yb3+ dimer.The glass and glass-ceramics samples with composition of 50SiO2–10AlF3–(30−x)BaF2–5TiO2–3.95LaF3– xMnCO3–0.05ErF3–1YbF3 (in mol%, x=0, 0.5, 0.8, 1.0, and 1.2) were prepared using the conventional quenching techniques. The effects of Mn2+ ions on the enhancement red upconversion emission of Mn2+/Er3+/Yb3+ tri-doped transparent glass-ceramics under the changing of heat treatment temperatures and concentrations of Mn2+ ions were investigated. The structural investigation carried out by X-ray diffraction (XRD), and transmission electron microscopy evidenced the formation of cubic Ba2LaF7 nanocrystals. The efficiency upconversion emission of Mn2+/Er3+/Yb3+ tri-doped was observed in the glass-ceramics. The upconversion mechanism and energy transfer between Mn2+–Yb3+ dimer and Er3+ ions were investigated.

A series of single-phased Bi3+, Eu3+, Tb3+ codoped Ca2Al2SiO7 phosphors have been prepared via high-temperature solid-state reaction. Energy transfer from Bi3+ to Eu3+ was observed and investigated in Ca2Al2SiO7 host matrix. By tuning the relative concentration ratio of Tb3+/Eu3+, Ca2Al2SiO7:Bi3+, Eu3+, Tb3+ phosphor has shown its color tunable capability, and a white light has been achieved by integrating the emission bands centered at 415(Bi3+), 542(Tb3+), and 619 nm(Eu3+), respectively. Our results indicated that Ca2Al2SiO7:Bi3+, Eu3+, Tb3+ phosphor provides a potential candidate for phosphor converted light-emitting diodes.Highlights► Energy transfer from Bi3+ to Eu3+ was investigated. ► Color tunable from Bi3+ to Eu3+ can be achieved by Bi3+, Eu3+-codoped Ca2Al2SiO7. ► White light can be realized in Ca2Al2SiO7:Bi3+, Eu3+, Tb3+ phosphor.

The up-conversion of Er3+/Yb3+ co-doped transparent glass-ceramics 50SiO2-10AlF3-5TiO2-30BaF2-4LaF3-0.5ErF3-0.5YbF3 containing Ba2LaF7 nanocrystals under the changing of heat treatment temperature and time were investigated. The Ba2LaF7 nanocrystals precipitated from the glass matrix was confirmed by X-ray diffraction (XRD). The structural investigation carried out by XRD and transmission electron microscopy (TEM) evidenced the formation of cubic Ba2LaF7 nanocrystals with crystal size of about 14 nm. Comparing with the samples before heat treatment, the high efficiency up-conversion emission of Er3+/Yb3+ co-doped samples was observed in the glass-ceramics under 980 nm laser diode excitation. The increase in red emission intensity bands was stronger than the green bands when the crystal size increased. The mechanism for the up-conversion process in the glass-ceramics and the reasons for the increase of Er3+/Yb3+ co-doped up-conversion intensity after heat treatment were discussed.High resolution transmission electron microscope image after heat-treated at 630 °C for 3 h (Inset: the selected area electron pattern)

The Bi–Er co-doped lanthanum aluminosilicate glasses, which exhibited a broadband near-infrared emission, were developed and observed in using the optical absorption and photoluminescence spectra. A super broadband near-infrared emission extending from 1.0 to 1.8 μm with a full-width at half-maximum of 450 nm which covered the whole O, E, S, C and L bands, was observed in Bi–Er co-doped samples under 808 nm excitation, as a result of the overlap of the Bi-related emission band (1270 nm) and the emission from Er3+4I13/2 → 4I15/2 transition (1545 nm). This report will discuss about a possible mechanism for energy transfer between Bi-related centers and Er3+ ion.Highlights► Bi/Er co-doped lanthanum aluminosilicate glasses have been developed. ► The NIR emission with a FWHM of 450 was observed under the 808 nm excitation. ► The mechanism of energy transfer between Bi+ and Er3+ was proposed. ► This material provides potential applications in the broadband optical amplifiers.

•White light photo-stimulated luminescence was observed.•The introduction of Dy3+ can generate traps with different depths.•The intensity of higher temperature bands (T2 and T3) increased.The optical storage properties of CSSO:Dy as a function of the dysprosium concentration were investigated. Following 980 nm excitation, the photo-stimulated luminescence of white-light was first observed in CSSO:Dy. TL curves revealed that there existed three types of trap (T1, T2, T3) in CSSO:Dy corresponding to the temperature bands, located at 300, 424 and 525 k, respectively. With increasing dopant contents, the amount of the deep traps (T2 and T3) increases, whereas the shallow traps concentration decreases. The results demonstrate that the optical storage ability of CSSO:Dy is enhanced with increasing Dy3+ contents at room temperature.Graphical abstract

•We prepared Tm3 +/Tb3 +/Yb3 + co-doped glass-ceramics containing Ba2LaF7 nanocrystals.•The emission intensity in the glass-ceramics has significantly enhanced after heat treatment.•There was possibly an energy transition process between Tb3 + and Tm3 + ions.The energy transfer and upconversion emission of Tm3 +/Tb3 +/Yb3 + co-doped transparent glass-ceramics 50SiO2–10AlF3–30BaF2–5TiO2–4LaF3 (SABTL) containing Ba2LaF7 nanocrystals under the changing of heat treatment temperatures and concentrations of Tm3 +/Tb3 +/Yb3 + ions were investigated. The structural investigation carried out by X-ray diffraction (XRD) and transmission electron microscopy evidenced the formation of cubic Ba2LaF7 nanocrystals. The efficiency upconversion emission of Tm3 +/Tb3 +/Yb3 + ions was observed in the glass-ceramics. The upconversion emission and energy transfer between Tm3 + and Tb3 + ions were investigated with the Yb3 + ions cooperatively upconversion emission, energy transfer between Tm3 + and Tb3 + ions.

A series of single-phased CaAl2Si2O8: Eu, Tb phosphors have been synthesized at 1400 °C via a solid state reaction. The emission bands of Eu2+ and Eu3+ were observed in the air-sintered CaAl2Si2O8: Eu phosphor due to the self-reduction effect. Tb3+ ions that typically generated green emission were added in CaAl2Si2O8: Eu phosphor for contributing for a wider-range tunable emission. Energy transfer from Eu2+ to Tb3+ and the modulation of valence distribution of Eu2+/Eu3+ that contributes to the tunable color emitting were elucidated. More importantly, a white emission can be obtained by controlling the codoped contents of Li+ as well as suppressing the self-reduction degree of Eu. The white light emitting with the color coordinate (0.326, 0.261) was obtained, which indicates that CaAl2Si2O8: Eu, Tb is a promising tunable color phosphor for application in ultraviolet light emitting diodes (UV-LEDs).Graphical abstractHighlights► Both the emission of Eu2+ and Eu3+ were observed due to the self-reduction effect. ► Energy transfer from Eu2+ and Tb3+ in CaAl2Si2O8 were elucidated. ► The modulation of valence distribution of Eu2+/Eu3+ were discussed in detail. ► White emission can be obtained by controlling the codoped contents of Li+.

The SiO2: Tb, Yb inverse opals with photonic band gap at 465 or 543 nm were prepared, and an effect of photonic band gap on upconversion spontaneous emission from Tb3+ was investigated. The results show that the photonic band gap has a significant influence on the upconversion emission of the SiO2: Tb, Yb inverse opals. The upconversion luminescence of the Tb3+ ions is suppressed in the inverse opal compared with the luminescence of that of the reference sample.Highlights► Upconversion emission from Tb3+ was observed in the SiO2: Tb, Yb inverse opal. ► UC emission of Tb3+ was modulated by controlling the structure of inverse opal. ► UC emission of Tb3+ was depressed in the inverse opal.

The Bi–Tm co-doped SiO2–Al2O3–La2O3 (SAL) glasses, which exhibited a broadband near-infrared (NIR) emission was investigated by the optical absorption and photoluminescence spectra. The super broadband near-infrared emission from 1000 to 2100 nm, which covered the whole O, E, S, C and L bands, was observed in the Bi–Tm co-doped samples, as a result of the overlap of the Bi-related emission band (centered at 1270 nm) and the emission from Tm3+3H4→3F4 transition (1440 nm) as well as Tm3+3F4→3H6 transition (1800 nm). Relative luminescence intensity at 1270, 1440 and 1800 nm wavelength varied depending on the mixing ratio of Bi and Tm and the full-width at half-maximum (FWHM) extending from 1000 to 1600 nm could be 400 nm. These results indicated that Bi–Tm co-doped SiO2–Al2O3–La2O3 glasses could provide potential applications in tunable lasers as well as the broadband optical amplifiers in WDM system.Highlights► The fluorescence of Bi–Tm co-doped SiO2–Al2O3–La2O3 glasses were investigated under 808 nm excitation. ► A NIR broadband luminescence with a full-width at half-maximum (FWHM) of 400 nm from 1000 to 1600 nm was observed. ► The mechanism of energy transfer between Bi+ and Tm3+ was presented. ► This material provides potential applications in the broadband optical amplifiers in WDM system.

Influence of competition between excited-state absorption and spontaneous emission from intermediate excited state on upconversion emission was investigated firstly in photonic crystals. The result clearly shows that upconversion emission can be modulated by the photonic crystal. When upconversion emission band from intermediate excited state overlaps with the photonic band gap, short wavelength unconversion emission from upper state is obviously enhanced due to an inhibition of spontaneous emission from the intermediate excited state in the photonic crystal. We believe that the present work will be valuable for not only the foundational study of upconversion emission modification but also new optical devices in upconversion displays and short wavelength upconversion lasers.Highlights► Upconversion (UC) inverse opal (LaPO4:Yb, Tb) photonic crystals were prepared. ► An enhancement of excitation state absorption was realized in the inverse opal. ► UC emission suppression from intermediate excited state was detected in inverse opal. ► An enhancement of UC emission from upper excited state was obtained.

Glasses with compositions of 34.5SiO2–25AlPO4–12.5Al2O3–12.5B2O3–15R2O–0.5Bi2O3 (R = Li, Na, K) were synthesized. Characteristic absorption bands of bismuth centered at 500, 700, and 800 nm and broadband near infrared (NIR) emissions peaked at 1100 and 1300 nm were observed. With the change of alkali ion (Li+ → Na+ → K+), the intensity of absorption bands at 500 and 800 nm increase, while the intensity of two NIR emissions decrease. The dependence of NIR emission peaked at 1300 nm on the radius of the alkali ion is found to be opposite to that in previous reports, being ascribed to the abnormal reduction of Bi ion in the glasses investigated herein. The results of this work is helpful for understanding the nature of Bi-NIR-emission, and the NIR emission peaked at 1300 nm was proposed to originate from Bi+ according to the influence of the alkali ions sizes.Highlights► NIR emission from Bi-doped aluminophosphsilicate glasses increase with increase in alkali ion radius. ► Tetrahedral anion groups in glass host can stabilize low valent Bi ions. ► NIR emission at 1300 nm was proposed from Bi+ according to the charge and the radius of alkali ion.

The optical properties of Eu-activated CaAl2Si2O8 appear to be totally dependent on the atmosphere during the synthesis processing. Compared with oxidizing/reducing-sintered samples, a significant enhancement in both the photoluminescence and afterglow for the vacuum-sintered sample is observed. The deficiency of energy transfer among the different emission centers is the prevailing contribution to the highest photoluminescence intensity of the vacuum-sintered sample. A distinction in afterglow characteristics of CaAl2Si2O8:Eu prepared in different atmosphere is suggested to be mainly due to the distribution of different trap depths at three types of emission centers.Graphical abstractHighlights► Optical properties of CaAl2Si2O8:Eu prepared in different atmosphere were different. ► Vacuum sintered CaAl2Si2O8:Eu exhibited enhanced photoluminescence intensity. ► The afterglow properties were improved of vacuum sintered CaAl2Si2O8:Eu.

Upconversion inverse opal photonic crystals based on a luminescent matrix of Yb, Er co-doped Y2Ti2O7 were synthesized, and their photoluminescence was investigated. By comparing the spectra of the inverse opals with that of the reference sample, the contribution of photonic band gap effect to the upconversion emission was observed in the Y2Ti2O7: Yb, Er inverse opals. Intensity of the green or red upconversion emission from Er3+ was depressed when the overlapping between the photonic band-gap and Er3+ ions emission band occurs.Highlights► A novel upconversion (UC) inverse opal (Y2Ti2O7:Yb, Er) was prepared. ► UC emission of Er3+ was modified by controlling the structure of inverse opal. ► Suppression of the red or green UC emission was detected in the inverse opal.

The Bi–Tm–Er co-doped SiO2–Al2O3–La2O3 (SAL) glasses, which exhibited a broadband near-infrared (NIR) emission, were investigated by the optical absorption and photoluminescence spectra. A super broadband NIR emission extending from 0.95 to 1.6 μm with a full-width at half-maximum (FWHM) of 430 nm which covered the whole O, E, S, C and L bands, was observed in Bi–Tm–Er co-doped samples under 808 nm excitation, as a result of the overlap of the Bi-related emission band (centered at 1270 nm) and the emission from Tm3+3H4→3F4 transition (1450 nm) as well as Er3+4I13/2→4I15/2 transition (1545 nm). In addition, a super broadband emission with amplitude relatively flat from 0.95 to 2.1 μm has been observed. The possible energy transfer between Bi-related centers, Tm3+ ions and Er3+ ions was proposed.Highlights► Bi/Tm/Er co-doped lanthanum aluminosilicate glasses have been developed. ► Energy transfer was analyzed when pumped by conventional 800 nm LD. ► The broadband near-infrared emission from 950 to 2100 nm was observed. ► This material provides potential applications in the broadband optical amplifiers.

An effective approach to fabricate porous bone regenerative composite scaffolds with surface-immobilized nano-hydroxyapatite (nHA) is developed in this research. In the typical preparation process, surface-repellent stable colloidal nHA with surface carbonyl functionality was fabricated through in-situ polyvinyl pyrrolidone (PVP)-grafting synthesis without any organic solvents and potentially harmful additives. Followed by freezing and lyophilizing homogenous PVP-grafted nHA and chitosan mixtures, three dimensional nHA and chitosan composite scaffolds were then obtained. The TEM images and XPS analysis show that the discrete nHA was anchored at nano-level on the pore surface of chitosan scaffold by mediating PVP chemical-linkage. The PVP-grafting offers an efficient and safe approach to prepare nHA with the surface reactivity and is promising to be widely used in the fabrication of novel composite scaffolds for bone tissue engineering.Highlights► nHA with surface carbonyl functionality was synthesized safely through PVP-grafting synthesis. ► PVP-grafting provides nHA with effective colloidal stability and surface reactivity. ► Nano-level uniform dispersing and chemical-linkage immobilization of nHA on the surfaces of composite scaffolds was realized.

Tb3+–Yb3+ co-doped Ca5(PO4)3F inverse opal photonic crystals were prepared by a self-assembly technique in combination with a sol–gel method. Upconversion luminescence characteristics of the inverse opals were investigated. The results indicate that photonic band gap has a significant effect on upconversion luminescence of Tb3+–Yb3+ co-doped Ca5(PO4)3F inverse opal. Significant inhibition of the green or blue upconversion luminescence was inspected if the photonic band gap overlapped with the emission band of Tb3+ ions.

The effect of P2O5 on infrared luminescence properties of bismuth-doped SiO2–Al2O3–CaO (SAC) glass was investigated. Under excitation of 690 and 808 nm LD, two infrared emissions from bismuth ions central at 1100 and 1300 nm were observed, respectively. The addition of P2O5 was not only found to lead to the increase of full width at half maximum (FWHM) of two infrared emissions, but also result in intensity variety of the infrared emissions. The intensity of the infrared emission located at 1300 nm is reduced by a factor of 2, while the luminescence at 1110 nm is increased by a factor of 5. We propose that the infrared emissions at 1100 and 1300 nm may originate from different valence Bi ion in glasses. Compared with emission at 1300 nm, the infrared emissions at 1100 nm is more possibly from the transition of lower valent Bi ion.Highlights► P2O5 had inverse effect on the intensity of two broad infrared emissions of Bi ions centered at 1300 and 1100 nm. ► The addition of P2O5 brings out the broadening of full width at half maximum (FWHM) of these two infrared emissions. ► Infrared emissions at 1100 and 1300 nm originate from different valence Bi ion in glasses. ► The inverse effect of P2O5 on the two broad infrared emissions resulted from abnormal reducing process of glass structure.

Er3+/Yb3+ co-doped transparent glass-ceramics containing Ca5(PO4)3F nano-crystals were prepared and their upconversion properties were investigated. Transparent glass-ceramics were obtained after heat treatment at the first crystallization temperature, TEM images showed that Ca5(PO4)3F nano-crystals of 10–20 nm in diameter precipitated uniformly in the glass matrix, which is similar to the result of those calculated by Scherrer equation. Comparing with the samples before heat treatment, high efficiency upconversion luminescence of Er3+ at 547 nm and 667 nm was observed in the glass-ceramics under 980 nm excitation, and the intensity of red emission showed different tendency to that of green emission after nano-crystals precipitation. The reasons for the highly efficient upconversion luminescence in glass-ceramics were discussed.

The effect of optical basicity on Er3+ up-conversion luminescence in germanate glasses is investigated under 980 nm excitation. The intensity of green and red up-conversion luminescence decreased with the increase in radius of alkali ion or Li2O content, implying that up-conversion luminescence strongly relates to the optical basicity of glass host. On the other hand, as increasing the optical basicity, the red emission intensity decreased significantly, while the green emission intensity decreased slightly. It has been proposed that the up-conversion luminescence intensity was dominated by the optical basicity, which theoretically estimated from glass composition. The interaction mechanism between up-conversion process and optical basicity was proposed.

Upon excitation at 808 nm laser diode, an intense 1.47 μm infrared fluorescence has been observed with a broad full width at half maximum (FWHM) of about 124 nm for the Tm3+-doped TeO2-K2O-La2O3 glass. The Judd–Ofelt parameters found for this glass are: Ω2 = 5.26 × 10−20 cm2, Ω4 = 1.57 × 10−20 cm2 and Ω6 = 1.44 × 10−20 cm2. The calculated emission cross-sections of the 1.47 μm transition are 3.57 × 10−21 cm2, respectively. It is noted that the gain bandwidth, σe × FWHM, of the glass is about 440 × 10−28 cm3, which is significantly higher than that in ZBLAN and Gallate glasses, a high gain of 35.5 dB at 1470 nm can be obtained in a TKL glass fiber. TeO2-R2O (R = Li, Na, K)-La2O3 glasses has been considered to be more useful as a host for broadband optical fiber amplifier.

Upconversion (C) light-emitting photonic band gap materials (YBO3: Yb, Er) with inverse opal structure were prepared by a self-assembly technique in combination with a sol–gel method. The effect of the photonic stop-band on the upconversion luminescence of Er3+ ions has been investigated in the YBO3: Yb, Er inverse opals. Significant suppression of the green or red UC emission was detected if the photonic band-gap overlaps with the Er3+ ions emission band. We successfully achieved the color tuning of the UC optical properties of the inverse opal by controlling the structure of the photonic crystal.

Inverse opal photonic crystals of Y b3+, Er3+ co-doped TiO2 (TiO2:Yb, Er) were prepared by a self-assembly technique in combination with a sol–gel method. Upconversion (UC) luminescence properties of the inverse opals were investigated. The results show that photonic bandgap has significant influence on the upconversion emission of the TiO2:Yb, Er inverse opal photonic crystals. Significant suppression of the upconversion emission was detected if the photonic bandgap overlapped with the Er3+ ions emission band.Research highlights► A novel upconversion (UC) inverse opal (TiO2:Yb, Er) photonic crystals were prepared. ► Modification of UC emission was realized by controlling the structure of inverse opal. ► Suppression of the red or green UC emission was detected in the inverse opal.

Bismuth-doped alkaline metal germanate glasses with infrared fluorescence covering the whole low loss wavelength region were developed. The infrared fluorescence centered around 1.31 μm with the full width at half maximum (FWHM) lager than 200 nm was observed in GeO2–R2O–Bi2O3 (R = Li, Na, K) glasses under an 808 nm LD excitation, whereby the fluorescence lifetime is longer than 400 μs. These results indicate that the glass material may have potential applications in broadband optical amplifiers. The intensity of the infrared fluorescence decreases with the increase in the optical basicity of the host glasses. It is suggested that the fluorescence in the near infrared region should be ascribed to the low valence state of bismuth such as Bi2+ or Bi+, because a higher optical basicity favors the higher valence state of the multivalence metal ions.

Inverse opal photonic crystals of Y b3+, Er3+ co-doped TiO2 (TiO2:Yb, Er) were prepared by a self-assembly technique in combination with a sol–gel method. Upconversion (UC) luminescence properties of the inverse opals were investigated. The results show that photonic bandgap has significant influence on the upconversion emission of the TiO2:Yb, Er inverse opal photonic crystals. Significant suppression of the upconversion emission was detected if the photonic bandgap overlapped with the Er3+ ions emission band.Research highlights► A novel upconversion (UC) inverse opal (TiO2:Yb, Er) photonic crystals were prepared. ► Modification of UC emission was realized by controlling the structure of inverse opal. ► Suppression of the red or green UC emission was detected in the inverse opal.

A series of single-phased Ca2Al2SiO7:Eu2+ phosphors were synthesized by the solid-state reaction. Their structure and photoluminescence properties were investigated by the X-ray powder diffraction (XRD) and excitation and emission spectra in detail. The emission spectra of Ca2Al2SiO7:Eu2+ phosphors consisted of blue and green band located at 419 and 542 nm, respectively. The relative intensities of the blue and green emission changed with Eu2+ concentration and were sensitive to the excitation wavelength. The unique photoluminescence property originated from the 4f7→4f65d transition of Eu2+ at different energy levels, on which the effect of the crystal field strength was considered to be tailed by adjusting the host composition.