Influence of HIP post-treatment on the microstructure and luminescent properties of SPSed Al2O3-Ce:YAG composite ceramics

Fine-grained Al2O3-Ce:YAG composite ceramics with 0.05-0.3 at% Ce3 + doping were prepared by single reactive spark plasma sintering (SPS) and a two-step approach combining SPS and hot isostatic pressing (HIP) techniques. It was revealed that application of HIP provided additional homogenization of the Ce:YAG solid solution throughout the material volume, while changes in the recrystallization kinetics of constituent phases contributed to the stabilization of garnet/alumina grains sizes. An increase in external quantum efficiency in the series up to 72 % and 76 % was observed with saturation occurring at 0.2 at% Ce3+. The synchrotron radiation luminescence (SRL) kinetics allowed distinguishing two modes. In comparison with PL kinetics, the underestimation of decay time tau slow values is explained by the SR effect, which similarly to the thermal effect can also induces the formation of radiation defects and the ionization of Ce3+ 5d electrons. Both PL and SRL studies revealed the presence of concentration quenching effect in phosphors with 0.3 at% Ce3+. Measurements under excitation by blue laser diodes (LDs) in the reflection mode showed that 0.1-0.2 at% Ce3+-doped samples after HIP treatment exhibited the most favorable characteristics for application in high-power white laser lighting. White LDs equipped with 0.4 mm-thick Al2O3-0.2 at% Ce:YAG showed an optimum correlated color temperature of 6499-6602 K, a high luminous flux of 222-2500 lm, and luminous efficiency of 242-232 lm & sdot;W- 1 as LD power increased from 0.8 to 9.5 W & sdot;mm- 2 .