Co-reporter:Yue Xu, Renli Fu, Simeon Agathopoulos, Xu Wang, Yang Yang, Junde Cai
Journal of Alloys and Compounds 2017 Volume 693() pp:454-461
Publication Date(Web):5 February 2017
DOI:10.1016/j.jallcom.2016.09.226
•The relationship between εr and ionic radius of the rare earth cations was confirmed.•The τf increased was confirmed due to the increase of cell polarization.•The dielectric properties is correlated to the level of distortion of the octahedral.The influence of substitution with rare earth elements in orthorhombic Ca0.66Ti0.66R0.34Al0.34O3 (R = Sm, Nd, La) perovskite ceramics, which were successfully produced with a solid-state reaction method, on their crystal structure (analyzed with Rietveld refinement of X-ray diffractograms and Raman spectroscopy) and on the microwave dielectric properties was investigated. The dielectric constant (εr) increased due to the increase of cell volume, which was a result of the increase of the ionic radius of the rare earth cations incorporated in the host lattice R3+. The values of the quality factors were 43620.74, 41292.71, and 38389.57 GHz for the Sm-, Nd-, and La-containing ceramics, respectively. The decrease of these values is correlated to the level of distortion of the octahedral due to the incorporation of the three different rare earth cations. The temperature coefficient of resonant frequency increased from 4.99 for the Sm-ceramics to 9.92 ppm/°C for the La-ceramics, attributed to the increase of cell polarization.
Co-reporter:Meng Fei, Renli Fu, Simeon Agathopoulos, Jun Fang, Caixia Wang, Haitao Zhu
Materials & Design 2017 Volume 130(Volume 130) pp:
Publication Date(Web):15 September 2017
DOI:10.1016/j.matdes.2017.05.067
•Al/AlN joints succeed prepared through a thick film method using CuO paste.•The Al/AlN joints strength reached 15.4MPa while heat treatment at 660 °C.•The Al2Cu second phase at interface have a great effect on the Al/AlN joints.A novel method for preparing aluminum/aluminum nitride ceramics (Al/AlN) substrates is proposed in this paper. The method included two processes: (1) the surface of AlN was coated with a CuO thick film and sintered; (2) Al foil was put on the pretreated (in process 1) AlN surface and bonded to AlN through pre-heating at 400 °C and final heating at 660 °C in N2-H2 reduction atmosphere. The experimental results obtained by optical and scanning electron microscope (SEM) observations as well as by X-ray diffraction analysis at the cross-sections of the joints and the fracture surfaces, suggest that the reaction mechanism starts with the reaction of CuO with AlN to form CuAlO2, when the AlN coated with CuO is heat-treated at high temperature. A Cu layer is produced by the reduction of CuO and Cu diffuses in the Al foil, forming strong Al/AlN joints. Elongated crystals of Al2Cu are developed in the reaction zone at the interface between Al and AlN. The results of mechanical tests showed that the peeling-off strength of the Al foil from the surface of the AlN substrate reached a value of 15.4 MPa for the Al/AlN couples produced after 30 min of heat treatment at 660 °C.Download high-res image (281KB)Download full-size image
Co-reporter:Yang Yang, Renli Fu, Simeon Agathopoulos, Yue Xu, Junde Cai
Ceramics International 2016 Volume 42(Issue 16) pp:18108-18115
Publication Date(Web):December 2016
DOI:10.1016/j.ceramint.2016.08.123
Abstract
Perovskite ceramics with a formula of Ca0.7Ti0.7La0.3Al0.3O3 (CTLA) were produced through a conventional solid-state reaction procedure following three different La3+-doping methods using powders of La2O3, or La2O3/Al2O3 powder mixture, or LaAlO3. La3+ doping favored grain growth and densification, affected the grain size distribution, and improved the dielectric properties of the produced sintered CTLA ceramics. The doping methods had a strong influence on these properties. More specifically, doping with La2O3 and La2O3/Al2O3 resulted in formation of solid solution, while a secondary phase formed in the CTLA ceramics doped with LaAlO3, which caused a coarsening of the microstructure and lowered the La3+ doping effects on the dielectric properties. The experimental results suggest that La3+ doping improves the dielectric properties of the sintered CTLA perovskite ceramics, which are further enhanced by doping with Al3+ ions in small amounts. However, further increase of Al3+ ions content jeopardizes them.
Co-reporter:Yue Xu, Renli Fu, Simeon Agathopoulos, Xu Wang, Yang Yang, Junde Cai
Ceramics International 2016 Volume 42(Issue 13) pp:14573-14580
Publication Date(Web):October 2016
DOI:10.1016/j.ceramint.2016.06.072
Abstract
BaO-Sm2O3-5TiO2 (BST5) ceramics with NdAlO3 additions of up to 15 wt% were produced with a solid state reaction method, and their structural and microwave dielectric properties were determined. Experimental results showed that NdAlO3 neither merged nor altered the orthorhombic tungsten bronze structure of the main phase of the produced ceramics (except for a shrinkage in the crystal lattice), but it was segregated in distinct grains in the microstructure of the produced ceramics. However, the amount of NdAlO3 strongly influenced the densification and the microstructure (i.e. grain shape and size) of the produced ceramics. Analysis of the experimental results suggests that the microstructural features can be correlated to the dielectric properties of these ceramics. Accordingly, the dielectric constant (εr) and the temperature coefficient of resonant frequency (τf) of the produced BLT5 ceramics can be tuned with the amount of NdAlO3 additions and the sintering process parameters. The best dielectric properties were achieved for BaO-Sm2O3-5TiO2 ceramics with 7.5% NdAlO3 (εr=73.22, Q×f =10,300 GHz, and τf=−1.05 ppm/°C).
Co-reporter:Xiguang GU, Renli FU, Fang YANG, Ye TANG, Jun FANG
Journal of Rare Earths 2016 Volume 34(Issue 11) pp:1089-1094
Publication Date(Web):November 2016
DOI:10.1016/S1002-0721(16)60139-4
A series of novel lanthanum strontium aluminate phosphors, Ce3+-doped LaSr2AlO(5–0.5x)Fx(LSAF) phosphors were successfully synthesized using the high-temperature solid state synthesis procedure under reducing atmosphere (H2/N2=1/4). The X-ray diffraction pattern revealed that LSAF sample was a pure LaSr2AlO5 phase with a sintering temperature of 1250 °C. With the increasing amount of SrF2, the particle size of powders increased and the shape of particles changed more regularly. Being an orange/red emitting phosphors for orange and white light emitting diodes, LSAF:Ce3+ could be effectively excited by blue lights with typical 4f→5d transitions of Ce3+ ions. PL and PLE spectra showed inhomogeneous enlargement effects with the increase of F/O ratios, which suggested that electronegativity effect was promoted when F/O ratio increased. This was further confirmed by a red shift of PL spectra peak when F/O was increased. It can be concluded that the LSAF:Ce phosphors have the potential to meet the development of white light-emitting diodes.SEM micrographs of LSAF:Ce with F/O=0 (a), 0.04 (b), 0.08 (c) and 0.12 (d), respectively
Co-reporter:Arzu Cosgun, Renli Fu, Weina Jiang, Jianhai Li, Jizhong Song, Xiufeng Song and Haibo Zeng
Journal of Materials Chemistry A 2015 vol. 3(Issue 2) pp:257-264
Publication Date(Web):14 Nov 2014
DOI:10.1039/C4TC02256D
Integration of blue light-emitting diode (LED) chips with yellow phosphors has been the most practical way to achieve white lighting, but finding a low-cost alternative for Y3Al5O12:Ce3+ (YAG:Ce) phosphors, which are expensive and lack red emission, is still a great challenge. The present report documents a strategy of combining quantum dot–polyvinyl alcohol (PVA) composites and blue chips for white LEDs. Cadmium-free and water-soluble ZnSe:Mn/ZnS quantum dots (QDs) were synthesized through a nucleation doping strategy, and then embedded in PVA. The flexible composite contains well-dispersed QDs and exhibits highly efficient photoluminescence at 590–635 nm, and hence is available for resin-free white LEDs. Besides excellent stability, the assembled white LEDs possess promising color characteristics, including a color rendering index (CRI) value of 93.5, a correlated color temperature (CCT) of 2913 K at Commission Internationale de l'Eclairage (CIE) color coordinates of (0.41,0.37), and a luminous efficacy (LE) of 18.9 lm W−1 under 300 mA current excitation. This work demonstrates that such a silica-coated QD–PVA composite plate, as a reliable color converter, would be promising for the next-generation QD-based LEDs.
Co-reporter:Xiguang GU, Renli FU, Weina JIANG, Pengfei ZHANG, Ye TANG, Arzu COŞGUN
Journal of Rare Earths 2015 Volume 33(Issue 9) pp:954-960
Publication Date(Web):September 2015
DOI:10.1016/S1002-0721(14)60511-1
LaSr2AlO5:Sm3+ phosphors were synthesized by the Pechini-type sol-gel process. The X-ray diffraction pattern revealed that a pure LaSr2AlO5 phase was obtained with a sintering temperature of 1200 °C. Microstructure characterization showed that the particles were spherical in shape with a mean size of 2.93 µm. Being a candidate orange/red emitting phosphor for orange and white light emitting diodes, LaSr2AlO5:Sm3+ could be effectively excited by both near-ultraviolet (NUV) and blue lights with typical f-f transitions of Sm3+ ions. The most intense emission corresponding to 4G5/2→6H7/2 (604 nm) could be achieved at the same Sm3+ concentration of 4 mol.%. The chromaticity coordinates of La0.96Sr2AlO5:0.04Sm3+ phosphor under the excitation of 407 and 458 nm were (0.57, 0.43) and (0.59, 0.38), respectively. Further study was carried out using Van Uitert's and Dexter's models. A consistent result was obtained that electric dipole-dipole interaction was dominant for the energy transfer among Sm3+ ions. The critical distance for energy transfer among Sm3+ ions in LaSr2AlO5 was calculated to be ca. 1.843 nm.PL spectra of the La1–xSr2AlO5:xSm3+ (x=0.005–0.15) phosphors excited at 407 nm (a) and at 458 nm (b)
Co-reporter:Pengfei Zhang;Weina Jiang
Journal of Materials Science: Materials in Electronics 2015 Volume 26( Issue 11) pp:8350-8357
Publication Date(Web):2015 November
DOI:10.1007/s10854-015-3501-6
The copper layer was deposited on the surface of Al2O3 ceramic substrate via thick film and nano-SiO2/copper electroless composite plating methods. The morphologies and phase compositions of the metalized copper layers on ceramic substrate were investigated by the means of scanning electron microscope and X-ray diffraction. The electrical conductivity, adhesion strength and thermal cycling reliability were studied by four-probe method, peel test and temperature cycling test, respectively. Nano-SiO2 had great influence on the morphologies of copper layer plating on the thick film ceramic substrate, the nano-SiO2 played a role of the nuclei action for the copper plating, especially for the cavity on the surface of thick film copper layer. The copper layer of nano-SiO2/copper electroless composite plating on the thick film ceramic substrate with 0.5 g L−1 of nano-SiO2 represented lower porosity and higher electrical conductivity. The electrical conductivity of copper layer was consistent with theoretical results based on the modified Huang’s formula. It is indicated that the electrical properties of nano-SiO2/copper electroless composite plating copper layer could be predicted by the two-phase composite rule. The optimum adhesion strength and thermal cycling times were obtained when the content of nano-SiO2 was 0.5 g L−1. The reasons of these phenomena were also discussed.
Co-reporter:Weina Jiang, Renli Fu, Xiguang Gu, Pengfei Zhang, Arzu Coşgun
Journal of Luminescence 2015 157() pp: 46-52
Publication Date(Web):
DOI:10.1016/j.jlumin.2014.07.018
Co-reporter:Fengjiao Qian, Renli Fu, Simeon Agathopoulos, Xiguang Gu, Xiufeng Song
Journal of Luminescence 2012 Volume 132(Issue 1) pp:71-75
Publication Date(Web):January 2012
DOI:10.1016/j.jlumin.2011.07.009
Single-phase broad-band red-emitting Ca3Si2O7:Eu2+ phosphors, with photoluminescence features that qualify them as candidates for white light-emitting diodes applications, were successfully synthesized via a modified solid-state reaction method that employed H3BO3 as a flux. The phosphors produced have an intense broad red emission band, with a peak at 603 nm, a full width at half maximum of 110 nm, and color coordinates of (0.550, 0.438). Concentration quenching occurred at 0.01 mol Eu2+. The discussion of the results shows that Eu2+ ions should be accommodated at the Ca-sites of the lattice, dipole–dipole interactions should predominantly govern the energy transfer mechanism among them, and the critical distance between them is ∼31 Å.Highlights► Pure Ca3Si2O7:Eu2+ phosphor was successfully synthesized by adding H3BO3 . ► Effects of H3BO3 on phase formation and emission intensity were presented. ► Luminescence properties in conjunction with Ca3Si2O7 structure were studied. ► Energy transfer mechanism of Eu2+ and its critical distance were proposed.
Co-reporter:Ran Li, Renli Fu, Xiufeng Song, Hong He, Xiaodong Yu, Bingbing He, Zhixiang Shi
Journal of Physics and Chemistry of Solids 2011 Volume 72(Issue 4) pp:233-235
Publication Date(Web):April 2011
DOI:10.1016/j.jpcs.2011.01.009
Tb-doped SrSi2O2N2 phosphors with promising luminescent properties were synthesized by the conventional solid-state reaction method, characterized by powder X-ray diffraction and studied by photoluminescence excitation and emission spectra. The synthesized materials exhibited a weak blue emission and a strong green emission in the region of 400–470 nm and 480–650 nm, which are attributed to 5D3→7Fj (j=5, 4, 3) and 5D4→7Fj (j=6, 5, 4, 3) transitions of Tb3+, respectively. The green emission from 5D4→7F5 at 543 nm showed the highest intensity under the optimized concentration of 0.1 mol, after which the quenching concentration became relevant. The quenching behavior of the emission of Tb3+ was explained by the cross-relaxation of its excited state.Research highlights► Well-crystallized Tb-doped SrSi2O2N2 phosphors were synthesized. ► The PL spectra showed a strong green emission between 480 and 600 nm. ► The maximum green emission intensities were obtained at 0.1 mol% of Tb3+ ions. ► The quenching behavior was confirmed to be a cross-relaxation process.
Co-reporter:Hong He, Xiufeng Song, Renli Fu, Zhengwei Pan, Xinran Zhao, Zhonghua Deng, Yongge Cao
Journal of Alloys and Compounds 2010 Volume 493(1–2) pp:401-405
Publication Date(Web):18 March 2010
DOI:10.1016/j.jallcom.2009.12.111
The crystal structure and photoluminescence properties of Eu2+ doped Li2Ca0.7Sr0.3SiO4 phosphors were investigated. The Li2Ca0.7Sr0.3SiO4 is not an alloy between the tetragonal Li2CaSiO4 and hexagonal Li2SrSiO4 but crystallizes in orthorhombic structure similar to Li2(CaSr)SiO4. Photoluminescence properties of the Li2Ca0.7Sr0.3SiO4:Eu2+ phosphors, summarized in effective excitation in the UV region, strong emission in the blue light range (with a peak at 427 nm) and the CIE chromaticity coordinate (0.154, 0.038), indicate this phosphor has great potential in UV-chip pumped white LEDs. White light output by mixing the Li2Ca0.7Sr0.3SiO4:Eu2+ blue and Li2SrSiO4:Eu2+ yellow phosphor was attempted. With proper molar ratio of these two compound phosphors, warm white light with CIE chromaticity coordinate close to that of the nature white light (0.33, 0.33) and color temperature about 5000 K was obtained. The results indicated that the Li2Ca0.7Sr0.3SiO4:Eu2+ may become an important phosphor candidate for ultra-violet chip pumped and multi-phosphors converted white LEDs.
Co-reporter:Hong He, Yongge Cao, Renli Fu, Wang Guo, Zhi Huang, Meili Wang, Changgang Huang, Jiquan Huang, Hai Wang
Applied Surface Science 2010 Volume 256(Issue 6) pp:1812-1816
Publication Date(Web):1 January 2010
DOI:10.1016/j.apsusc.2009.10.012
Abstract
The crystal structure, band gap energy and bowing parameter of In-rich InxAl1−xN (0.7 < x < 1.0) films grown by magnetron sputtering were investigated. Band gap energies of InxAl1−xN films were obtained from absorption spectra. Band gap tailing due to compositional fluctuation in the films was observed. The band gap of the as-grown InN measured by optical absorption method is 1.34 eV, which is larger than the reported 0.7 eV for pure InN prepared by molecular beam epitaxy (MBE) method. This could be explained by the Burstein–Moss effect under carrier concentration of 1020 cm−3 of our sputtered films. The bowing parameter of 3.68 eV is obtained for our InxAl1−xN film which is consistent with the previous experimental reports and theoretical calculations.
Co-reporter:Renli Fu, Simeon Agathopoulos, Xiufeng Song, Xinran Zhao, Hong He, Xiaodong Yu
Optical Materials 2010 Volume 33(Issue 1) pp:99-102
Publication Date(Web):November 2010
DOI:10.1016/j.optmat.2010.08.015
CaSi2O2N2 phosphors co-doped with Ce3+ and Eu2+ was synthesized via solid-state reaction method. The experiments aimed at optimizing the composition of those phosphors for achieving the highest luminescence intensity as well as at shedding light in the mechanism that governs their luminescence behavior. The overlap of the blue emission spectrum due to Ce3+ with the yellow excitation spectrum due to Eu2+ suggests resonance-type energy transfer mechanism from Ce3+ to Eu2+ taking place in the CaSi2O2N2 host lattice, where electric dipole–dipole interactions dominate. The properties of the produced phosphors qualify them for further consideration in the technology of white light-emitting diodes.
Co-reporter:Hong He, Renli Fu, Yongge Cao, Xiufeng Song, Zhengwei Pan, Xinran Zhao, Qingbo Xiao, Ran Li
Optical Materials 2010 Volume 32(Issue 5) pp:632-636
Publication Date(Web):March 2010
DOI:10.1016/j.optmat.2010.01.009
Co-reporter:Zhengwei Pan, Hong He, Renli Fu, Simeon Agathopoulos, Xiufeng Song
Journal of Luminescence 2009 Volume 129(Issue 9) pp:1105-1108
Publication Date(Web):September 2009
DOI:10.1016/j.jlumin.2009.05.011
Ba2+-doped Sr2SiO4:Eu2+ phosphors were synthesized with the high-temperature solid-state reaction technique. The experimental results, summarized in the successful production of a single-phase powder with fine microstructure of spherical particles with smooth surface, suggest that Ba2+-doping favors the stabilization of α′-Sr2SiO4. Rietveld refinement of X-ray diffractograms suggests that Ba2+ and Eu2+ ions occupy the sites of Sr2+ in the lattice of α′-Sr2SiO4. The produced phosphors show two intense emission bands at green and yellow regions of spectrum, originated from Eu2+ ions accommodated at two different sites in the host crystal, whose peaks depend on the concentrations of Ba2+ and Eu2+. Intense and broad excitation spectra extend from ultraviolet to the blue region.
Co-reporter:Jun Zeng;Yuan Shen;Hong He ;Xiufeng Song
Journal of Applied Polymer Science 2009 Volume 113( Issue 4) pp:2117-2125
Publication Date(Web):
DOI:10.1002/app.30045
Abstract
The epoxy molding compound (EMC) with thermal conductive pathways was developed by structure designing. Three kinds of EMCs with different thermal conductivities were used in this investigation, specifically epoxy filled with Si3N4, filled with hybrid Si3N4/SiO2, and filled with SiO2. Improved thermal conductivity was achieved by constructing thermal conductive pathways using high thermal conductivity EMC (Si3N4) in low thermal conductivity EMC (SiO2). The morphology and microstructure of the top of EMC indicate that continuous network is formed by the filler which anticipates heat conductivity. The highest thermal conductivity of the EMC was 2.5 W/m K, reached when the volume fraction of EMC (Si3N4) is 80% (to compare with hybrid Si3N4/SiO2 filled-EMC, the content of total fillers in the EMC was kept at 60 vol %). For a given volume fraction of EMC (Si3N4) in the EMC system, thermal conductivity values increase according to the order EMC (Si3N4) particles filled-EMC, hybrid Si3N4/SiO2 filled-EMC, and EMC(SiO2) particles filled-EMC. The coefficient of thermal expansion (CTE) decreases with increasing Si3N4 content in the whole filler. The values of CTE ranged between 23 × 10−6 and 30 × 10−6 K−1. The investigated EMC samples have a flexural strength of about 36–39 MPa. The dielectric constant increases with Si3N4 content but generally remains at a low level (<6, at 1 MHz). The average electrical volume resistivity of the EMC samples are higher than 1.4 × 1010 Ω m, the average electrical surface resistivity of the EMC samples are higher than 6.7 × 1014 Ω. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Co-reporter:Hong He;Xueliang Zhang
Journal of Materials Science: Materials in Electronics 2009 Volume 20( Issue 5) pp:433-438
Publication Date(Web):2009 May
DOI:10.1007/s10854-008-9747-5
Divalent europium activated alkaline earth orthosilicate M2SiO4 (M = Ba, Sr, Ca) phosphors were synthesized through solid-state reaction technique and their luminescent properties were investigated. Photoluminescence emission spectra of Sr2SiO4:Eu2+ phosphor was tuned by substitution of Sr2+ with 10 mol% Ca2+ or Mg2+. Two emission bands originated from the 4f–5d transition of Eu2+ ion doped into different cation sites in the M2SiO4 host lattice were observed under ultraviolet excitation. The Sr2SiO4:Eu2+ phosphor showed a blue and a green broad emission bands peaked around 475 and 555 nm with some variation for different Eu2+ doping concentration. When 10 mol% of Sr2+ was substituted by Ca2+ or Mg2+, the blue emission band blue-shifted to 460 nm and the green emission band shifted to even longer wavelength. An energy loss due to energy transfer from one Eu2+ to another Eu2+ ion, changing of the crystal field strength and covalence in the host lattice together were assigned for the tuning effect. With an overview of the excitation spectra and the emission spectra in blue and green-yellow color, these co-doped phosphors can become a promising phosphor candidate for white light-emitting-diodes (LEDs) pumped by ultraviolet chip.
Co-reporter:Xiufeng Song, Renli Fu, Simeon Agathopoulos, Hong He, Xinran Zhao, Jun Zeng
Materials Science and Engineering: B 2009 Volume 164(Issue 1) pp:12-15
Publication Date(Web):15 August 2009
DOI:10.1016/j.mseb.2009.06.005
Eu2+ and Mn2+ co-doped SrSi2O2N2 green-phosphors, with promising luminescent properties (examined by their powder diffuse reflection, photoluminescence excitation and emission spectra) suitable for UV converted white LEDs, were produced by high temperature solid-state reaction method. The produced materials exhibited intense broad absorption bands at 220–500 nm and a broad emission band centered at ca. 530 nm, attributed to 4f–5d transitions of Eu2+. The emission intensity of Eu2+ ions was greatly enhanced by introducing Mn2+ ions into SrSi2O2N2:Eu2+ due to the energy transfer from Mn2+ to Eu2+. The energy transfer probability from Mn2+ to Eu2+ depends strongly on the Mn2+ concentration, which is maximized at a Mn2+ concentration of 3 mol%. It drastically decreases for higher concentrations. The results indicated that SrSi2O2N2:Eu2+, Mn2+ is a promising green-emitting phosphor for white-light emitting diodes with near-UV LED chips.
Co-reporter:Hong He, Renli Fu, Xiufeng Song, Deliu Wang, Jiankang Chen
Journal of Luminescence 2008 Volume 128(Issue 3) pp:489-493
Publication Date(Web):March 2008
DOI:10.1016/j.jlumin.2007.09.023
Divalent europium-activated strontium orthosilicate Sr2SiO4:Eu2+ and Mg0.1Sr1.9SiO4:Eu2+ phosphors were synthesized through the solid-state reaction technique. Their luminescent properties under ultraviolet excitation were investigated. The X-ray diffraction (XRD) results show that these phosphors are of α′-Sr2SiO4 phase with a trace of β-Sr2SiO4. Doping of Eu2+ ion into the crystal lattice results in the lattice constant being expended, while Mg2+ makes the lattice constant shrinking. A solid solution with the same crystal structure is formed when Eu2+ or Mg2+ substitutes part of Sr2+ ions and occupies the same lattice sites. The Sr2SiO4:Eu2+ phosphors show two emission spectra peaked at 535 and 473 nm originated from the 5d–4f transition of Eu2+ ion doped in two different Sr2+ sites in the host lattice. By substitution of 0.1 mol of Sr2+ with Mg2+, these two emission bands are tuned to be in the blue and yellow region (459 and 564 nm for Mg0.1Sr1.88SiO4:Eu0.02), respectively. The tuning effect is discussed. With a combination of the blue and yellow emission bands the phosphors show white color, indicating that these phosphors may become promising phosphor candidates for white light-emitting diodes (LEDs).
Co-reporter:Arzu Cosgun, Renli Fu, Weina Jiang, Jianhai Li, Jizhong Song, Xiufeng Song and Haibo Zeng
Journal of Materials Chemistry A 2015 - vol. 3(Issue 2) pp:NaN264-264
Publication Date(Web):2014/11/14
DOI:10.1039/C4TC02256D
Integration of blue light-emitting diode (LED) chips with yellow phosphors has been the most practical way to achieve white lighting, but finding a low-cost alternative for Y3Al5O12:Ce3+ (YAG:Ce) phosphors, which are expensive and lack red emission, is still a great challenge. The present report documents a strategy of combining quantum dot–polyvinyl alcohol (PVA) composites and blue chips for white LEDs. Cadmium-free and water-soluble ZnSe:Mn/ZnS quantum dots (QDs) were synthesized through a nucleation doping strategy, and then embedded in PVA. The flexible composite contains well-dispersed QDs and exhibits highly efficient photoluminescence at 590–635 nm, and hence is available for resin-free white LEDs. Besides excellent stability, the assembled white LEDs possess promising color characteristics, including a color rendering index (CRI) value of 93.5, a correlated color temperature (CCT) of 2913 K at Commission Internationale de l'Eclairage (CIE) color coordinates of (0.41,0.37), and a luminous efficacy (LE) of 18.9 lm W−1 under 300 mA current excitation. This work demonstrates that such a silica-coated QD–PVA composite plate, as a reliable color converter, would be promising for the next-generation QD-based LEDs.
