Analysis of photoluminescence mechanisms and thermal quenching effects for multicolor phosphor films used in high color rendering white LEDs

In order to prepare phosphor-converted white LEDs with high color rendering index (CRI) and high luminous efficiency, the multicolor phosphor film by mixing more than two monochromatic phosphor powders in a silicone matrix is widely used. But usually its photoluminescence mechanism can't be explained by a simple superposition of each spectra emitted by individual monochromatic phosphors. Additionally, as being close to LED chips, the phosphor film is always suffered under high temperature when LED operates. Therefore, this study analyzes the thermal quenching effects of multicolor phosphor films prepared by mixing the Garnets, Silicates and Nitrides based phosphors in silicone. And their photoluminescence mechanisms are investigated by modeling of spectral power distributions (SPDs) for the prepared white LED chip scale packages (CSPs) through optical simulations with LightTools software. Through analyzing the features of emission spectra (e.g. emission peak, peak wavelength and full widths at half maximum (FWHMs)) from prepared multicolor phosphor films, the results show that the heat treatment leads to a significant decrease of luminous intensity, all peak wavelengths shift to the short-wavelength range and all FWHMs become narrow. However, these results are not simply the superposition of each thermal quenching effect of monochromatic phosphors and this nonlinearity is supposed to be caused by the reabsorption of luminescence between phosphor particles and multiple conversions among them.