A single-phased silicate compound （Ba1-xCex）9（Sc1-yMny）2Si6O24 was prepared by solid-state reaction at high temperature. From powder X-ray diffraction （XRD） analysis, the formation of Ba9Sc2Si6O24 with an R3 space group was confirmed. In the photoluminescence spectra under ultraviolet （UV） ray excitation, the Ba9Sc2Si6O24：Ce3＋,Mn2＋ phosphor emits two distinctive color light bands： a blue one originating from Ce3＋and a red one caused by Mn2＋. The energy transfer process from Ce3＋ to Mn2＋ was confirmed, the critical radius as well as the transfer efficiency was calculated, and the energy transfer mechanism was discussed. In addition, the decay-time testing indicates that the energy transfer efficiencies from Ce（1） to Mn2＋ and Ce（2） to Mn2＋ are different. The emission chromaticity of Ba9Sc2Si6O24：Ce3＋,Mn2＋ phosphor could be tuned from blue to red by altering the Ce3＋/Mn2＋ concentration ratio.
The dependences of light efficiency of radiation （LER） and color-rendering index （CRI） of trichromatic white light-emitting diode （wLED）, composed of blue LED die, green/yellow, and red phosphors, on the peak wave- length of each primary were investigated by theoretical calculations, at correlative color temperature （CCT） from 2,700 to 6,500 K. The peak wavelength of InGaN based blue LED chip ranges from 450 to 471 nm, while those of Ca3Sc2Si3012：Ce3＋, b-SiA1ON：Eu2＋, and Y3A15012：Ce3＋ based green/yellow phosphors range from 511 to 572 nm, and those of Sr2SisN8：Eu2＋ and CaA1SiN3：Eu2＋ red phosphors range from 620 to 650 nm, which cover almost all the practically used, commercially available wave bands until now. Then, based on the results, selection guides of peak wavelengths for blue LED chip and phosphors to obtain tradeoff LER 〉280 lm.W-1 as well as CRI 〉80 in all CCTs are proposed. The favorable wave bands of each primary are suggested.
Dong-Chuan ChenZhen SongZhu-Guang LiuZhong-Hua DengLan WuYong-Ge CaoQuan-Lin Liu
Using ray-tracing simulation based on Monte Carlo method, the effects of phosphor concentration and thickness on light output and phosphor consumption of pcwLEDs were investigated in this work. The simulation was improved to comprehensively imitate the whole optical process of pc-wLEDs, including total produce of chip and phosphor light, losses in the propagation, and output.Experiments were conducted to verify the simulation.Results show that, light output changes non-monotonously over phosphor concentration and thickness, having maximum value. Experimental maximum light efficiency of158 lmáW-1was obtained at concentration of 16 wt%, 6 %higher than that of 11 wt% and 17 % higher than that of 33wt%. Phosphor consumption of pc-wLEDs increases linearly with the increase of phosphor concentration and the decrease of thickness. Experimental phosphor consumption of pc-wLEDs with concentration of 11 wt% is only 37 %of that of 33 wt%.
Trivalent cerium-doped yttrium aluminum garnet （YAG：Ce3＋） phosphors are synthesized by solid-state reaction method through using （Yl-xCex）203 solid solutions as precursors. Solid solubility limits of Ce3＋ replacing y3＋ in Y203 and YAG are determined to be 40% and 7.5%, respectively, based on the relationship between the lattice param- eter and chemical composition. Using （Y1-xCex）203 as precursors we synthesize YAG：Ce3＋single phase at 1450 ~C and N2 atmosphere. However, under the same conditions using CeO2 there exists a second phase YA103 as impurity. The photoluminescence intensity of YAG：Ce3＋ increases monotonically with the increase of Ce concentration until it reaches a maximum at solid solubility limits of Ce3＋ in YAG.
Bond valence method illustrates the relation between valence and length of a particular bond type. This theory has been used to predict structure information, but the effect is very limited. In this paper, two indexes, i.e., global instability index（GII） and bond strain index（BSI）, are adopted as a judgment of a search-match program for prediction. The results show that with GII and BSI combined as judgment, the predicted atom positions are very close to real ones. The mechanism and validity of this searching program are also discussed. The GII ＆ BSI distribution contour map reveals that the predicted function is a reflection of exponential feature of bond valence formula. This combined searching method may be integrated with other structure-determination method, and may be helpful in refining and testifying light atom positions.
In this study, small- and large-particle-diameter phosphor powders were mixed together（hybrid phosphors）to balance light efficacy and angular color uniformity and pursue optimal results. Phosphor with small-particlediameter of 4 lm was employed and it was mixed into each large-particle-diameter phosphor of 10, 16, 22, and 26 lm,at mass percentage from 0 % to 50 % with an interval of10 %, respectively. Remote phosphor package was adopted and overall phosphor concentration was kept constant for better comparison. Moreover, absorption coefficient labs,scattering coefficient lscaand extinction coefficient lext of each hybrid phosphors were calculated based on Mie theory to further discuss the experiment results. Results show that, the introduction of small-particle-diameter phosphor to large one can highly improve angular color uniformity while only slightly reduce light efficacy. The optimal performance with angular color uniformity of91.6 % as well as normalized light efficacy of 95.7 % is achieved in the white light emitting diode with hybrid phosphors consisting of 60 wt% powder of 22 μm and40 wt% powder of 4 μm.
Dong-Chuan ChenZhu-Guang LiuZhong-Hua DengChong WangYong-Ge CaoQuan-Lin Liu
