| Due to the energy-saving, environment-friendliness, high-reliability, long-lifetime characteristics, high-power white light-emitting diode (LED) packages are considered as the fourth generation light sources and have penetrated into every aspect of our daily life. LED packages based on blue LED chip and yellow phosphors are the most widely used scheme to produce white light, which is the right study object of this thesis. Phosphor, as a kind of photoluminescent materials, determines the optical parameters of white LED packages, like correlated color temperature (CCT), angular color temperature (ACU), color rendering index (CRI), and so forth. Meanwhile, phosphors also generate heat during the photoluminescence process, which will influence the heat dissipation of LEDs. In order to realize good optical and thermal performances of phosphors, we couple the optical and thermal properties to study on phosphors in this thesis, and applied the research results to develop new coating processes. Achievements are as follows:1) Based on the Mie theory, the optical constants of phosphor particle were calculated, including the absorption coefficient, scattering coefficient, anisotropic parameter, etc. With considering the light absorption, scattering and conversion of phosphor particles simultaneously, the single-and multi-layer optical models for phosphors were established by modifying the conventional Kubelka-Munk theory. The established model is much closer to the real situation than the conventional one. And the phenomenon of the phosphor particle sedimentation was analyzed by the multi-layer model. Besides, we discovered the "near-field effect" of the color mixing in single white LED module for the first time.2) The effective thermal conductivity of phosphor silicone matrix was calculated by2D/3D model based on unit cell method. With experimental validation, the error was less than5%. The method to probe phosphor temperature was proposed based on magnetic nanoparticles and the results showed that LED chip temperature was326.8K, while phosphor temperature was374.8K at input voltage of5.2V. Through thermal reliability test at real time, the LEDs with high phosphor temperature turned to have severe luminous decay, and decreasing phosphor temperature was proved to be an effective way to restrain this luminous decay. Therefore, decreasing phosphor temperature is a necessary way to realize high performance white LED packages.3) The optical-thermal coupled model for phosphors was established and the formula of phosphor heat generation was derived. The influence of phosphor parameters on phosphor heat generation was analyzed based on the model. By considering the phosphor heat generation, the "hotspot shift" phenomenon, which varies with the change of phosphor concentrations and locations, was observed in white LED packages for the first time. The phosphor particle distribution in the silicone matrix was optimized based on genetic algorithm and the methods to decrease phosphor temperature were proposed.4) Many phosphor coating processes were proposed base on the optical-thermal coupled model of phosphors. The parameters of phosphor conformal coating were optimized and the ideal thickness was about50-70μm; a novel primary freeform lens to realize phosphor conformal coating and uniform illumination simultaneously was proposed; the double-layer phosphor configuration that could enhance light extraction efficiency as high as17.63%was proposed.
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