| With the development of science and the popularization of LED,more and more places begin to use LED as lighting source.In addition to the increasing efficiency of light source,the quality of light source is also becoming more and more important.The quality of light source is generally evaluated by two points:spatial uniformity of light distribution and color rendering of light source.The former can be measured by color temperature uniformity or intensity uniformity of light source,while the latter can be evaluated by color rendering index.At present,red quantum dot phosphors are usually added to white LED to increase its color rendering.In this paper,the illumination characteristics of quantum dot phosphors,especially the scattering characteristics of quantum dot phosphors,are investigated by establishing the simulation of pc-LEDs.Finally,a new coating structure is proposed to improve the uniformity of color temperature and color rendering of pc-LEDs.Firstly,the simulation model of pc-LEDs is established by Monte Carlo method,including chip luminescence model,photon packet transmission model,phosphor scattering model,phosphor layer structure model and boundary processing model,coordinate transformation model after scattering,and Russian roulette model to optimize simulation speed.Then the scattering model of quantum dot phosphors is determined and applied in simulation.The parameters of the scattering model of quantum dot phosphors are determined by comparing simulation with experiment.The scattering coefficient is0.98)8)-1 mand the absorption coefficient is 2.78)8)-1.The final results are in good agreement with the experimental results.Based on the simulation,the scattering model of LED nano-particles is analyzed.Firstly,the importance of the correct scattering model to the final result is analyzed.The difference between Rayleigh scattering and H-G scattering is about 1.6 times.Then,an optimized scattering phase function is proposed by using the coefficients of H-G scattering phase function and Rayleigh scattering phase function.The form of the phase function is relatively simple,which meets the requirements of Monte Carlo method and will not be used at the same time.When the new scattering phase function with the same coefficient is introduced into the simulation,it is found that when the coefficient is 1/4,it is the best fit for the scattering of 100 nm titanium dioxide.In this paper,a new type of optimized phosphor coating structure is proposed,which is based on the traditional dispensing phosphor layer plus adaptive phosphor layer.Using the above simulation results,it is found that the color temperature uniformity of the self-adaptive phosphor layer is better than that of the single self-adaptive phosphor layer.By comparing the optimized coating with the single adaptive phosphor layer,it is found that the spatial color temperature uniformity of the former is better than that of the latter.The standard deviation of space color temperature of optimized coatings is 45.5K,while that of self-adaptive coatings is 177.8K.The ACU of optimized coatings is only0.96,and that of self-adaptive coatings is 0.84.Then we compare the traditional phosphor layer with the traditional phosphor layer.The results show that the standard deviation of space color temperature of the latter is 95.2K and ACU is 0.94,which indicates that the optimization results improve the uniformity of space color temperature compared with the latter.The optimization of the powder-to-binder ratio of the traditional dispensing phosphor layer and the exposure times of the adaptive phosphor layer in the coating were also studied.Finally,on the basis of optimizing the structure,the research on improving the color rendering is carried out.The results show that after adding red quantum dot phosphor,the color rendering ability has been greatly improved.The color rendering index has increased from an average of less than 30 to about 90,and the value of R9 has also increased from a negative number to about 90. |
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