Design And Fabrication Of YAG:Ce-Al₂O₃ Composite Phosphor Ceramics For Laser Lighting Applications

Solid state laser lighting is a newly emerging technology,which has been widely concerned by the researchers due to its high luminous efficacy,high brightness,long lifetime and non-toxic materials,and it is a new generation of subversive semiconductor lighting technology after LED lighting.This technology combines a blue laser diode(LD)with a yellow-emitting phosphor converter to achieve ultra-high brightness white laser light.The inevitable "efficacy droop" of InGaN-based light-emitting diode(LED)chips makes it quite difficult to realize high-power and high-brightness white light using a single chip.Differing from LED,InGaN-based LD can maintain high efficiency even at an input laser power density as high as 250 Wmm-2 and thus allow for an extremely high output luminous flux.Considering that the high light fluxes involved as well as the resulting in more conversion loss which generates great self-heating from the incident laser,this new technology draws a demanding requirement on the thermal performance of the color converter.It is efficient to enhance thermal conductivity and conversion efficiency of color converters by appropriate compositional design and microstructural tailoring.In this work,we proposed the self-thermal management YAG:Ce-Al2O3 composite ceramic color converters that consist of luminescent YAG:Ce phosphor particles embedded in a thermally conductive Al2O3 matrix,which allows to combine with high-power blue laser diodes to create super-high brightness white laser-driven light without using any heat sink.The thermal conductivity of the composite phosphor ceramics increases linearly from 10.2 to 32.5 Wm-1K-1 as the Al2O3 content varies from 0 to 90 wt%.Impressively,the composite ceramic with 60 wt%Al2O3 can withstand an incident laser power density up to 20.1 Wmm-2.A high-brightness white laser-driven light is obtained with the luminance of 982 Mcdm-2.Moreover,the secondary Al2O3 particles also act as scattering centers and enhance the light conversion efficiency.A maximum luminous efficacy of 157 1mW-1 is achieved under 11.94 Wmm"2 blue laser excitation at the Al2O3 content of 24 wt%,increased by 27.4%compared to the Al2O3-free YAG:Ce ceramic.The as-designed YAG:Ce-Al2O3 composite phosphor ceramics thus validate their great suitability in high-power and high-brightness laser-driven solid-state lighting.