A series of Yb3+-Er3+ coactivated La(Nb1-x,V-x)O-4 (0 <= x <= 1) upconversion (UC) emission phosphors are prepared by high-temperature solid-state reaction method. Experimental results demonstrate that the introduction of V5+ expands and distorts the unit cell volume of LaNbO4, and induces structural transformation of LaNbO4 from Phase 1 with monoclinic fergusonite structure (0 < x <= 0.2) to Phase 2 with tetragonal scheelite structure (0.25 <= x <= 0.5) to Phase 3 with monoclinic monazite structure (x=1). Under 976 nm excitation, continuously enhanced green UC emission is observed in Phase 1 with gradual replacement of Nb5+ with the V5+ (0 < x <= 0.2). At x=0.2, the luminescence intensity is enhanced 1.3 times than that of the pristine sample. In Phase 2 and Phase 3, the intensity of green UC emission is decreased gradually with increasing the V5+ concentration. Based on the XRD results and crystal structural analysis, the enhanced luminescence is attributed to the lowered symmetry around La3+ ions (Er3+ ions), which relaxes the parity-forbidden selection rules of Er3+ luminescent centers. This study provides a useful approach in developing UC luminescence materials with controllable optical properties based on variations in local coordination environments through composition substitutions. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Si4+ was introduced to the lattice of LiEuMo2O8 by solid-state reaction to prepare a new kind of red-emitting LiEuMo2-xSixO8 (0 < x <= 0.5) phosphors. The introduction of Si4+ ion caused the distortion and slight shrinking of the unit cell of LiEuMo2O8 material, and the blue-shift of the charge-transfer-absorption (CTA) band of LiEuMo2O8. Photoluminescence excitation (PLE) and photoluminescence measurements showed that the introduction of Si4+ was able to enhance the excitation efficiency of LiEuMo2O8 in NUV spectral region (360-400 nm). Consequently the red emission of LiEuMo2O8 phosphor was improved by 30% at x=0.2 under 395 nm light excitation, without loss of color purity. The enhanced red emission of LiEuMo2-xSixO8 was discussed in terms of the blue-shift of CTA band and the relaxation of parity-forbidden selection rules for trivalent europium luminescent centers. (C) 2010 Elsevier B.V. All rights reserved.

The La2Ti2O7:Pr3+, which emits red color luminescence upon UV light excitation, is prepared by the conventional high-temperature solid-state method and its luminescent properties are systematically investigated. X-ray diffraction, photoluminescence, afterglow emission spectra and long-lasting phosphorescence (LLP) decay curves are used to characterize this phosphor. After irradiation by a 290-nm UV light for 3 min, the Pr3+-doped La2Ti2O7 phosphor emits intense red emitting afterglow from the 1 D2 → 3H4 transitions, and its afterglow can be seen with the naked eye in the dark clearly for more than 1 h after removal of the excitation source. The afterglow decay curve of the Pr3+-doped La2Ti2O7 phosphor contains a fast decay component and another slow decay one. The possible mechanism of this red light emitting LLP phosphor is also discussed based on the experimental results.

采用高温固相法分别合成了不同Ce浓度掺杂的和固定Ce浓度为0.06不同Gd浓度掺杂的Y3Al5O12（YAG）系列荧光粉,通过测量其激发、发射光谱、漫反射光谱、荧光寿命和变温发射光谱,研究了掺杂元素的浓度对荧光粉发光性能的影响以及荧光粉发光的温度猝灭性质。研究结果表明:荧光粉发光强度随着Ce3+掺杂浓度和Gd3+掺杂浓度的提高均呈下降趋势。分析发现,荧光粉发光强度下降并非主要由浓度猝灭所引起,而是由于高浓度掺杂下发生YAG基质与Ce3+对激发光的竞争吸收,导致Ce3+对激发光的吸收量减少,从而影响发光强度。温度实验表明,随着温度的升高,荧光粉发光强度下降。Ce含量的改变对YAG:Ce荧光粉的热猝灭性质影响较小,Gd的掺杂使荧光粉的发射波长向长波方向移动,同时热猝灭现象严重。

Two series of Y3-xCexAl5O12 and Y2.94GdyCe0.06Al5O12 phosphors were synthesized by high-temperature solid reaction method. The influences of doped elements on the luminescence properties were studied by measuring excitation spectra, emission spectra, reflectance spectra, fluorescence lifetimes and the dependence of luminescence intensity on temperatures. The results show that the intensity of the luminescence decreases with the increase of doping concentration. The luminescence decrease is attributed to the partly absorbed excitation photons by YAG host. It means that the host with high doping competes with Ce3+ center for absorbing excitation energy. The competition leads to less Ce3+ excited and weaker luminescence intensity. The luminescence intensity in YAG:Ce phosphors is affected by temperature significantly, and the intensity of the luminescence decreases with the increase of temperature. Moreover, the thermal quenching of YAG:Ce phosphors is affected strongly by the concentration of Gd rather than Ce.

Tb-doped 12CaO x 7Al2O3 (C12A7:Tb3+) powders with strong green emission were prepared using the sol-gel method. X-ray diffraction, micro-Raman spectra, scanning electron microscopy and absorption spectra showed that C12A7:Tb3+ powders with grain size of 200-300 nm were synthesized. Porous powders could be formed as the concentration of Tb3+ was 5 at%. The absorption band around 209 nm was attributed to the host lattice absorption, and the bands around 255 nm and 274 nm were related to the 4f-5d transitions of Tb3+. The absorption intensity of the visible region was enhanced due to the presence of one 100 nm-diameter hole in every grain of C12A7:Tb3+ powders. The emission spectra showed noticeable influence of Tb-Tb cross relaxation, which favored the green photoluminescence (PL) over the blue PL. The study on the concentration quenching indicated that the energy transfers depopulating the 5D3 and 5D4 levels were assigned to the mechanisms of electric dipole-dipole and exchange interaction, respectively.

Recently, people are seeking the lighting source which consumes less energy and has no pollution. Light Emitting Diode (LED) has the advantages over the traditional lamps in the future. The luminous efficiency of blue-light chip and the conversion efficiency of phosphors determine the luminous efficiency of white light LEDs.The thesis experimentally demonstrates luminous efficiency of large-area, high-power blue-light LEDs. We study the high power blue LED and discover the influence of temperature and current on luminous efficiency. When operation temperature increases from 327 K to 380 K,the light efficiency of LED decreases 20%.The temperature rising,the radiation at the potential well decreases, so as to decrease the luminous efficiency. When operation current increases from 50 mA to 350 mA, the luminous efficiency of LED decreases 35%.The current increasing,the more nonequilibrium electron diffuse out of the potential well,so as to decrease luminous efficiency. Enhancing the heat dissipation efficiency and increasing the width of potential well can improve the luminous efficiency. LED should be working under the limit temperature and the saturated current.LED can work at high current relatively when the thermal dissipation is good. The heating generation will decay the lighting performance. Therefore, the thermal dissipation controls the development of the LED and the goal of our investigation is to increase the efficiency of the thermal dissipation. A good packaging technology is the way to solve the heat dissipation problem. But it is a challenge to develop this technology in the limited space of LED.The purpose of heat dissipating technology for LED is to decrease the working temperature of LED's chip.It is necessary to reduce the thermal resistance of LED package.The efficiency and reliabi-lity of solid state lighting devices depends strongly on successful thermal management,because the junction temperature of the chip is the prime driver for effective operation.As the power density continues to increase,the integrity of the package electrical and thermal interconnects become extremely important.

In this article,all the white LEDs are obtained from the GaN-based blue emitter plus a cerium doped yttrium aluminum gargnet (YAG:Ce) phosphor.Here we brought up a new method.Under certain ideal condition,we have rough estimated the color coordinates and the luminous flux about the white light LEDs with the new method.The color coordinates of the referenced white spectrum is (0.325,0.332),the color rendering index is 81.5 and the color temperature is 5 914 K.All the parameters of the referenced white spectrum are similar to the standard white LED spectrum of (0.33,0.33).Based on the referenced spec- trum,we simulated it and got the radiation intensities of the blue chip and the phosphor independently.By adjusting the proportion of the radiation intensities of the blue chip and the phosphor,we got some new white LED spectra.And here we defined the luminous flux of the referenced spectrum is 100 lm and the total pho- tons of all the white LEDS is equal to the referenced white LED spectrum.Also the conversion efficiency is supposed to 100%.In the range of (x,y) = [0.33,0.33](±0.05),we calculated the luminous flux of different color coordinates around the standard point.We find that the color coordinate of the maximum lumi- nous flux is at (0.35,0.38)and the luminous flux is 112 lm,the color coordinate of the minimum luminous flux is at (0.29,0.28)and the luminous flux is 93.5 lm.So we can know that the luminous flux dispersion can reach about 18.5% relative to the referenced point 100 lm.From the above results,when the luminous flux becomes the main parameter of all the white LEDs'parameters,we can know that if we want to get higher luminous flux white LEDs,we should control the quantity of the phosphor to make the color coordinate around the point (0.35,0.38).Another experiment has been done too in this article.According to the data in the experiment,the changing trend that the luminous flux increases with the increasing of color coordinate is inos- culated to the calculated results.And we also find that the luminous flux dispersion 28.1% is much larger than the calculated result,so the controlling of the color coordinate becomes more important.The main reasons of the different dispersions between theoretical calculation and experiment have been concluded as follows: First,the quantum conversion efficiency is supposed to 100% in the calculation,but it can't reach in the ex- periment.Second,the blue chips are different types and even they are from the same silicon slice,they can't be the same completely.Third,the unavoidable errors that exist in the experiment influence on the results.

The luminescence properties of Ce3+ ions in yttrium aluminum garnet(YAG) powder have been studied.The addition of 5% NH4F flux is equivalent to decrease the preparation temperature by 200 ℃.Since the ionic radius of Ce3+(0.128 3 nm) is a little larger than that of Y3+(0.111 59 nm),one can expect that Ce3+ experiences a strong crystal field in YAG:Ce.If all the added Ce3+ ions enter into the crystal lattice,substitute the sites of Y3+ ions,and then are incorporated as Ce3+ at undisturbed Y3+ sites,the reagent need to absorb plentiful Joule heat.The content of cerium determines the preparation temperature,more cerium means higher preparation temperature.We consider that the NH4F flux has no effect on the growth of YAG:Ce crystallite because of its low melting point.In order to improve the fluorescence intensity of green-yellow-emitting phosphor based on YAG:Ce for white LED(light-emitting diode),the effect of BaF2 and MgF2 as charge compensators were studied separa-tely.But the charge compensating mechanism has seldom been reported before.When the charge compensator and NH4F were jointly added,the intensity of emission was enhanced.When the charge compensator is MgF2,the intensity of phosphor YAG:Ce has the strongest brightness.The photoluminescence intensities of YAG:Ce phosphor particles with Ba2+,Mg2+ doped were about 135%~142% of that of YAG:Ce phosphor particles without charge compensator.This result can be explained in terms of the environment of trivalent cerium in the crystal structure of YAG.On one hand,we postulate that the oxygen vacancy formed upon calcining in a reductive atmosphere is the most important intrinsic defect.A compensation mechanism expected for YAG:Ce with Mg2+ codoped is provided by the association of two Mg2+ ions with an oxygen vacancy.In this case,the introduction of Mg2+ ions in YAG:Ce takes place in accordance with the scheme:This scheme implies that at certain cerium concentrations a single oxygen vacancy can be compensated by two Mg2+ ions.On the other hand,Ce3+ and MgF2 dopants have counteracting effects on the lattice parameter of cubic YAG.Ce3+ ions,which replace Y3+ of YAG to form a substitutional solid solution,cause an increase in the lattice parameter as the ionic radius of Ce3+ is larger than that of Y3+,while Mg2+ ions leads to a decrease in the lattice parameter because the ionic radius of Mg2+(0.086 nm) is smaller than that of Y3+.Further more,Mg2+ can substitute Y3+ easily without disturbing the crystal lattice.The addition of BaF2 as charge compensator acts as the role of MgF2.Differently,Ce3+ and BaF2 dopants don't have counteracting effects on the lattice parameter of cubic YAG(the ionic radius of Ba2+is 0.135 nm,larger than Ce3+ and Y3+).The lattice parameter expands because of a repulsive interaction between cations.The effect of doping on the optical behavior of YAG is even more complex.To analyze the role of charge compensator on the luminescent emission property of YAG:Ce,the synthesized products were characterized by XRD,photoluminescence emission and excitation spectra(PLE).

White light-emitting-diodes(LEDs) are known as a new generation lighting source.The luminous flux,color temperature and color rendering property are the three main index in light source.Using a blue LED with a phosphor layer which is excited by blue light and down-converting to the second light,such as yellow light,white light can be produced.Now white-LED is a hot-spot of research,the point of designing white-LED used for lighting is its colour temperature and efficience,and the phosphor layer in white-LED is very important to this.The placement of the phosphor,the geometry of the encapsulation dome,and the reflector cup influence on the optical loss,and hence on the device efficiency.We can find the energy loss term in the one-dimensional model and observe the phosphor layer thickness and boundary effect.Finally we can optimize the phosphor-type white LED package to obtain higher light extraction efficiency.Recently,it has been demonstrated that a large separation between the phosphor and the primary LED emitter,which we refer to as remote phosphor arrangement,enhances the phosphorescence extraction by reducing the optical power absorbed by the LED chip.The experimental enhancement of phosphor efficiency is 24% for blue-pumped yellow phosphor at 20 mA forward current.This improvement is mainly due to the reason:the phosphor-on-top arrangement reduces absorption of phosphorescence the LED chip.it is not known what will happen to the yellow light when it strikes the phosphor medium.To the best of our knowledge,there are no past studies that have quantified the transmission and reflection properties of light outside the excitation wavelength region of YAG:Ce phosphor.By analysing,the color coordinate,color temperature,Luminous flus,Lumen efficiency varied with forward current.From the result of the experiment,we know that color coordinate x and y is minish varing slowly with the increasing forward cureent.The color coordinate and the color temperature is the same uptrend.The luminous flux increases with increasing forward current,but the lumen efficiency decreases with increasing the forward current.

利用发射波长为470nm的蓝光发光二极管作为基础光源,通过荧光粉转换方法制备白光发光二极管,荧光粉主要采用稀土激活的铝酸盐Y3Al5O12∶Ce3+ (YAG).在工作电流为15mA条件下,所研制的白光LED的法向光强为2 890mcd;色坐标为x=0.29,y=0.33;显色指数为77;流明效率为14.9 lm/W.研究制备了不同色温的白光LED,色温范围从2 700～8 000K,研究了色温与色坐标之间的对应关系.并且与国外同类产品进行比较,部分指标已经超过了国外同类产品水平.

The most important background of white LED is green lighting source.The color coordinate and color index are very important for lighting source.In this paper,the color coordinate and color index of white light emitting diode are shown.The average value of color coordinate X,Y are 0.31 and 0.33,respectivily;the maximum value are 0.32,0.35;the minimum value are 0.29,0.29.The average value of color index is 80;the maximum is 83;the minimum is 78.

采用荧光粉转换的方法制备了纯绿色LED,所制备的纯绿光LED的发光峰值在520nm,其半峰宽约为30nm,法向光强为600mcd.

The present invention belongs to the fields of light emitting and display technology and is the wavelength converting and combining method of making ultrviolet light diode emit white light. The mixture phosphor powder of Y3Al5O12:Ce3+.Mn2+ and Ca8Zn(SiO4)Cl2 can emit white light of 380-700 nm in the excitation of 380 nm light. That is, the yellow light emitting material and blue light emittign material are mixed and the mixture is coated to ultraviolet light diode core to emit white light. The coated white light diode has high convension efficiency and good color developing performance and isa generation is solid power-saving green light source.

本文主要利用白光LED单管制备了白光LED面阵，将制备的白光LED面阵与日亚公司的同类产品进行了对比。研究了不同电流条件下，亮度、流明效率、色坐标和显色指数的变化。

重点对近年来白光LED的进展进行评述,同时介绍一些在这方面的研究结果.