Al2O3–Ce:YAG and Al2O3–Ce:(Y,Gd)AG composite ceramics for high brightness lighting: Effect of microstructure

Abstract The paper studies efficient Al2O3–Ce:YAG and Al2O3–Ce:(Y,Gd)AG composite ceramic phosphors produced by reactive vacuum sintering. As one of the possible routes for microstructure optimization, effect of isothermal holding time was considered. The correlation between microstructural parameters (the ratio of average grain size of the matrix and thermally stable phase, residual porosity, grain and pore size distributions) and photoluminescent properties of sintered composite ceramics after combining them with a blue light-emitting diode was identified. The differences in thermal quenching behavior between Ce-doped and Ce,Gd-codoped systems were also discussed. The highest luminous efficiency of almost 151 lm/W (4526 K) and 133 lm/W (3808 K) was obtained for Al2O3–Ce:YAG, Al2O3–Ce:(Y,Gd)AG phosphors with garnet/alumina size ratio of 2.1 and 1.6, residual porosity of P = 0.0065 and 0.0047 vol%, respectively.