Preparation And Properties Of Lu₃Al₅O₁₂:Ce³⁺ Ceramic Phosphors For Laser Diode Lighting

Laser diode（LD）driven lighting is regarded as the next-generation solid-state lighting,and has important applications in the fields of automobiles,aerospace,military and civilian special lighting,etc.Combining blue LD with phosphors is the main way to achieve LD lighting.The high power density of LDs has sparked a revolution in packaging technology from phosphors combine organic binders to remote encapsulations.Lu₃Al₅O₁₂:Ce³⁺(LuAG:Ce³⁺)ceramic phosphors（CPs）with high efficiency and superior thermal stability are considered to be the best type for high power LD lighting.In this dissertation,aiming at the problems of lattice and color center defects,luminescence saturation,and low color rendering of LuAG:Ce³⁺CPs,the research on the relationship of component designing-preparation technology-microstructure-LD performance was carried out.The main contents are as follows:（1）To avoid the lattice defects formed by the charge difference between Si⁴⁺in the sintering aid of ethyl orthosilicate and Al³⁺,a strategy of Ba²⁺-Si⁴⁺co-substituting Lu³⁺-Al³⁺with charge balance was proposed.The effects of Ba²⁺-Si⁴⁺co-substitution on crystal structure,luminescence properties,thermal stability were studied.A positive correlation between thermal stability performance and luminescence saturation performance was observed.Combining atmospheric annealing technology to control oxygen vacancy defects and Ce³⁺valence state,the performance of LuAG:Ce³⁺CPs significantly improved.Correspondingly,the saturation power density exceeded 19.75W/mm²,and the maximum luminous efficiency(LE_max)increased from 43.4 to 213.7lm/W.Based on the higher sintering activity of Al₂O₃ nano powders,the second phase was precipitated in-situ at the grain boundaries.Due to the pinning effect,the uniform refinement of the grains is achieved.Simultaneously,the CPs intensity was significantly improved.The control of the internal microstructure of the CPs combined with the modification of the surface morphology,the LE_max of the LuAG:Ce³⁺CP increased to272.6 lm/W.（2）The effect of charge balance co-substitution of alkaline earth metal ions A²⁺(Mg²⁺,Ca²⁺,Sr²⁺,Ba²⁺)and Si⁴⁺on the saturation performance and efficiency of LuAG:Ce³⁺CPs was studied in detail.The Mg²⁺,Ca²⁺,Sr²⁺reduced the saturation power density and efficiency,which may be attributed to the lower lattice stability caused by the smaller cation size.Ba²⁺-Si⁴⁺slightly improved the performance of CPs,and the LE_max reached 278.4 lm/W.The effect of Ce³⁺concentration on the conversion performance from laser to green light of LuAG:Ce³⁺CPs was studied,and the cross-relaxation between Ce³⁺ions significantly affected thermal stability and optical properties was observed.When the lowest Ce³⁺concentration is 0.05 at.%,the maximum power density of the CP improved to 31.21 W/mm²,and the corresponding luminous flux was 5526.1 lm.With the increase of Ce³⁺concentration,the saturation power density and luminous flux of CPs decreased linearly.Furthermore,the LE_max and external quantum efficiency both increased first and then decreased.The LE_max reached 280.1 lm/W when the optimal Ce³⁺concentration was 0.35 at.%.（3）To solve the problem of low color rendering of LuAG:Ce³⁺CPs,the strategies of adjusting the crystal field by component designing,co-doping of luminescent ions,and supplementary red light components were explored.Among them,a series of（Lu/Y/Gd）₃（Al/Ga）₅O₁₂:Ce³⁺garnet solid solution structure CPs were prepared.The emission peak position red-shifted from 520 to 576 nm and the peak width extended to132 nm.The color rendering index（CRI）increased from 49.5 to 63.5.Due to the energy transfer between Ce³⁺and Pr³⁺ions,the LuAG:Ce³⁺,Pr³⁺CPs realized the 610 nm red light spectrum complementation under blue LD excitation,and the CRI increased by23.6%.Further,by designing a ceramic/film stack structure,the LuAG:Ce³⁺CP acted as a good thermal conductive substrate and a high-efficiency green light-emitting body.Combined with the red phosphor-in-glass film,the CRI of the LuAG:Ce³⁺CP increased to 74.5,the maximum power density was 14.65 W/mm²,and the LE_max maintained204.2 lm/W,which is expected to be applied to white LD lighting.