Preparation And Properties Of Hot Pressing Sintered Ce:YAG Phosphor Transparent Ceramics For Laser-driven Lighting

High-power laser lighting technology is an emerging semiconductor lighting technology with the advantages of high light extraction efficiency,high luminous brightness and small volume to volume ratio.Conventional white light conversion materials such as phosphors cause severe heat loss under high-power operation due to low thermal conductivity,making the luminous efficiency of the light emitting device（LED）drop significantly.Therefore,Ce:YAG transparent ceramics have been proposed because of their high doping concentration,high thermal conductivity and structural design flexibility.As well,Ce:YAG transparent ceramic materials are generally considered to be one of the most researched colour conversion materials for high-power white LED/LD lighting.In this work,Ce:YAG transparent ceramics with high transmittance properties were prepared by high-temperature solid phase reactions combined with vacuum hot pressing（HP）using commercially available primary powders.Because of the irregular particle distribution of the initial powder and the low sintering activity,optimisation of commercial powders was analysed by adjusting the ball milling process parameters,the addition of ball milling dispersants and the optimum calcination temperature.The problem of carb on contamination caused by graphite moulds in HP sintering has been solved by optimizing the HP sintering preparation process through the study of various options in this topic.Due to the deficient of the red spectrum of Ce:YAG ceramics,different concentrations of Mn²⁺as red light elements were doped to improve the colour rendering index of the samples.The microstructure and luminescence properties of Ce,Mn:YAG fluorescent transparent ceramics with different doping contents were analysed.The main conclusions of the research achieved were as follows.（1）The ball milling processes of grading of ballstone,ratio of material,ball and ethanol,ball milling speed and ball milling time were systematically studied using a ball milling process experimental design,and combined with SEM and particle size distribution.The best ball milling process parameters for this study were as follows:small ball,medium ball,large ball with a ratio of 1.5:1.5:0.5;material,ball and ethanol ratio of 1:3:1;ball milling speed of 250 r/min;and ball milling time of 24 h.The PEI dispersant was shown to be effective in promoting ball milling efficiency and the optimum calcination conditions of 800°C and 3 h for the mixed powders were determined.（2）The graphite moulds used in HP sintering caused serious carbon contamination to the samples.In this work,a HP sintering process with excellent carbon elimination was discovered through the study of various treatment methods.This method was:wrapping BN around the exterior of the sintered greenbody to avoid direct contact between the samples and the graphite mould on a physical level and to reduce the possibility of carbon contamination entering the sample through solid phase diffusion.On the other hand,Li F was doped during the preparation of the ceramics as a sintering aid to prevent carbon contamination;carbon contamination entering the interior of the samples was eliminated during HP sintering.The use of this two-step method for the elimination of carbon contamination had enabled the preparation of Ce:YAG transparent ceramics with excellent microstructure,high densities and high optical transmittance properties.The sample achieved a linear transmittance of 71.5%at 800 nm under a low vacuum pressure of 10^-1 Pa,a pressure of 50 MPa and a holding time of 1 h at 1600°C.（3）In order to improve the luminescence performance of Ce:YAG transparent ceramics,the physical structure and microscopic morphology analysis of Mn²⁺-doped Ce:YAG transparent ceramics with different concentrations were investigated in HP sintering,and the change of the fluorescence excitation and emission spectra of the samples were analysed.The LED/LD luminescence performance of samples doped with different amounts of Mn²⁺was investigated by photoelectric analysis tests and integrating spheres in combination with LED chips.