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A homogeneous co-precipitation method was developed to synthesize well dispersed yttrium aluminum garnet (YAG, Y 3 Al 5 O 12 ) powders. This method ensures the co-precipitation of Y 3+ and Al 3+ , solving the problem of differential precipitation of Y 3+ and Al 3+ in the conventional homogeneous precipitation method. Furthermore, the pH value can be controlled to be a plateau (around 5.2) during the titration process due to the continuous decomposition of the heated urea which can compensate for the pH reduction when adding the mother salts, which is beneficial to the narrow size distribution of the precipitates. Pure YAG nanopowders can be obtained at 900 °C without the formation of impurity phases such as YAM (Y 4 Al 2 O 9 ) or YAP (YAlO 3 ). The resultant YAG powders are well dispersed and have excellent sinterability that can be sintered into transparent ceramics at 1700 °C by vacuum sintering. [ABSTRACT FROM AUTHOR]

High-brightness laser lighting requires high luminous efficacy and high thermal performance of luminescent materials. In this study, we designed and fabricated single-phase YAG:Ce ceramics with differential grain sizes by combining the coarse commercial phosphor and fine powder of precusor. The large YAG:Ce grains mainly contribute to excellent luminescence properties. The small YAG:Ce grains not only change the direction of light propagation to improve the luminous efficiency but also effectively increase the Ce3+ content to improve the absorption of blue light, which significantly further enhance the luminescence properties compared with the second phase in the YAG:Ce-base composite ceramics. The luminescent ceramic with 40 wt% large grains sintered under 1550 °C has the highest luminous efficacy of 398.5 lm/W. Compared with the Al 2 O 3 –YAG:Ce composite ceramic, the single-phase YAG:Ce ceramic effectively increased the absorption of blue light to enhance the luminescence properties without the adverse effects caused by the transverse scattering of light in the Al 2 O 3 phase. After encapsulating the ceramic onto a radiator, a high luminous flux of 7697.6 lm under the blue-laser excitation of 3.0 A (54.6 W) was obtained. These indicated its broad application prospects in high-power solid-state laser lighting. [ABSTRACT FROM AUTHOR]

The miniaturization of high-brightness white light-emitting diodes (WLEDs) is limited by the low thermal performance of phosphors. In this study, the microstructure, optical properties, and thermal performance of Al 2 O 3 –Y 3 Al 5 O 12 :Ce3+ (Al 2 O 3 –YAG:Ce) composite ceramics fabricated by hot pressing were investigated. By promoting the growth of Al 2 O 3 grains while maintaining a high composite density, thermal performance of the composite ceramics was significantly increased. The thermal conductivity of a Al 2 O 3 –40-vol% YAG:Ce ceramic reached 21.8 W/m/K, which is close to the theoretical value. In addition, this composite ceramic exhibited the highest energy efficiency. After packaging with a high-power LED chip with dimensions of 1 mm × 1 mm, a high luminous flux of 639 lm was generated, while the reduction in output power at 250 °C was as low as 6%. This indicated excellent high-temperature stability and potential for applications in solid-state lighting. [ABSTRACT FROM AUTHOR]

Yb:YAG (yttrium aluminum garnet) transparent ceramics were fabricated by the solid-state method using monodispersed spherical Y 2 O 3 powders as well as commercial Al 2 O 3 and Yb 2 O 3 powders. Pure YAG phase was obtained at low temperature due to homogeneous mixing of powders. Under the same sintering conditions, the Yb:YAG ceramics with different doping contents of Yb3+ had similar morphologies and densification rates. After being sintered at 1700 °C in vacuum, the ceramic samples had high transparencies. The Yb:YAG ceramics doped with 0.5 wt% SiO 2 formed Y–Si–O liquid phase and nonstoichiometric point defects that enhanced sintering. Compared with Nd doping, Yb doping hardly affected the YAG grain growth, sintering densification or optical transmittance, probably because Yb3+ easily entered the YAG lattice and had a high segregation coefficient. [ABSTRACT FROM AUTHOR]