Effect of Surface Roughness on Luminescence Performance of Phosphor Ceramics
Objective Ce∶Y3Al5O12 and Al2O3 composite phosphor ceramics(Ce∶YAG-Al2O3)exhibit high thermal conductivity,excellent thermal stability,high phosphor conversion efficiency,and high luminescence quenching power.Hence,they are considered as the most suitable candidate for high-power excitation and are widely used in traffic signal displays,street lighting,car lighting,home lighting,stadium lighting,liquid crystal display backlights,and full-color displays.The luminescence mechanism and preparation process of Ce∶YAG-Al2O3 composite phosphor ceramics have been extensively studied.However,there is a paucity of studies on the cutting process and packaging technology of phosphor ceramics,which are crucial for the performance of lighting devices comprising blue light emitting diodes/laser diodes(LEDs/LDs)and phosphor ceramics.Therefore,this study focusses on Ce∶YAG-Al2O3 composite phosphor ceramic and systematically examines the effect of thickness and roughness on the luminescent properties of phosphor ceramics.Methods Blue LED chips were used to excite the Ce∶YAG-Al2O3 composite phosphor ceramic in transmission mode.Furthermore,the Ce∶YAG-Al2O3 composite phosphor ceramic was cut into 13-mm diameter discs with a laser and polished with boron carbide polishing powder.The effect of the annealing treatment on the luminescence performance of the phosphor ceramic and the variation in the luminescence performance of the phosphor ceramics with different thickness and surface roughness values were systematically examined.Furthermore,different surface roughness values for the blue light incident surface and light-emitting surface were formed using different types of boron carbide polishing powder,which were used to explore the mechanism of the influence of surface roughness on luminescence performance.The photoluminescence(PL)spectra and optoelectronic data of the phosphor ceramic were obtained using a high-precision rapid spectroradiometer equipped with an integrating sphere.The results provide valuable reference for the cutting process and packaging technology of phosphor ceramics.Results and Discussions The results show that annealing can significantly improve the luminescence performance of phosphor ceramics owing to the removal of surface impurities.As the thickness of the phosphor ceramics increases,the intensity ratio of transmitted blue light to yellow-green light emitted by the phosphor ceramics decreases,the color temperature decreases,and the luminescence efficiency increases.Increasing the surface roughness of ceramics can significantly improve the luminous efficiencies of phosphor ceramics.However,the roughness of the blue light incident surface or the light-emitting surface alone slightly affects the luminescent performance of Ce∶YAG-Al2O3 composite phosphor ceramics.Therefore,the influence of roughness on the luminescence performance emerges from multiple factors,including the roughness of the blue light incident surface and the photoluminescence quantum efficiency of Ce∶YAG-Al2O3 composite phosphor ceramics.The test results indicate that the phosphor ceramic sample exhibits the low roughness for the blue light incident surface and high roughness for the light-emitting surface,which is beneficial for reducing the color temperature of the phosphor ceramic and improving its luminous efficiency.Conclusions Thickness and surface roughness can be used to adjust the luminescence performance of phosphor ceramics.Increasing the thickness of the phosphor ceramic results in an increase in the amount of yellow-green light relative to blue light in the PL spectra of the phosphor ceramic,a decrease in the color temperature,and an increase in the luminous efficiency.Inducing surface roughness can significantly improve the performance of high-power white LEDs based on phosphoric ceramics.Furthermore,annealing has a positive effect on the luminescence properties of phosphor ceramics.These results lay a foundation for the development of high-power light devices based on Ce∶YAG-Al2O3 composite phosphor ceramics.
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