Optical Behavior Of YAG:Ce³⁺@SiO₂ Phosphor Used For White LED Chip Scale Packages

As a new package structure of light-emitting diodes(LED)package,chip scale packages(CSP)is used in lighting fields with high color quality and high power and high brightness.In the CSP LED,a blue light LED chip is usually covered with a layer of yellow fluorescent film to generate white light.The fluorescent film is composed of Y_3-xCe_xAl₅O₁₂(YAG:Ce³⁺)phosphor particles and silica gel mixed in proportion.The optical constants(scattering coefficients,absorption coefficients,anisotropy coefficients)of the fluorescent film are affected by the size of the phosphor particles,the morphology,concentration.Therefore,the accuracy of the optical constants of the fluorescent film is essential for the CSP package.Vital.After the phosphor particles are coated,the optical constants of the fluorescent film will change.Many scholars have conducted experimental analysis on phosphor coating,but the mechanism by which phosphor coating can improve light efficiency has not been studied.Meanwhile,after the phosphor particles are coated,the optical constants of the fluorescent film has not been calculated.This topic studies the effect of phosphor coating on light output.Using a new type of CSP,taking YAG and YAG@SiO₂(YAG surface coated with nano-SiO₂ layer)as examples,The impact was systematically analyzed:(1)In this paper,YAG and YAG@SiO₂ are taken as examples to analyze the light absorption and scattering of a phosphor particle coating and multiple phosphor particles coating before and after460 nm excitation light and 550 nm non-excitation light.The reasons why the coating can improve the light efficiency are studied and verified by experiments.(2)In order to ensure the correct modeling of the LED CSP package,the optical constants of the fluorescent film were calculated,and the Mie scattering theory was used to analyze the optical constants of YAG and YAG@SiO₂ by the coating amount,the particle size of the phosphor,and the phosphor concentration.It is found that the smaller the particle size of the phosphor,the greater the effect of the coating amount on scattering coefficients and absorption coefficients.The coating thickness is 20 nm,and the absorption coefficient increases the most,which is conducive to increasing the absorption of blue light and photoluminescence,so that the amount of yellow light emitted is increased;the decrease in the scattering coefficient is also conducive to improving the light efficiency.(3)Using the Monte Carlo method,using the CSP chip as a carrier,the effects of the fluorescent film before and after coating on the light efficiency and color temperature were studied,and the forward scattering of the fluorescent film before and after coating was analyzed with 460 nm and 550nm incident light.Combined with optical constants,we analyzed the effect of YAG@SiO₂ on luminous efficiency and color temperature.Under the thickness of the fluorescent film is 2?m,the fluorescent film composed of a phosphor particles with a radius of 2?m covers 20 nm SiO₂ layer with a light efficiency of 138 lm/W,color temperature of 6637 K,and color coordinate of(0.3110,0.3244).This article uses the YAG@SiO₂ layer as an example to provide other scholars with a new idea and technical support for the improvement of light efficiency by phosphor coating.