Temperature Effect on the Optical Properties of YAG and Silicate Phosphor-based White Light Emitting Diodes

Abstract

Two white light emitting diodes(LEDs) were fabricated by using two kinds of yellow phosphor, YAG:Ce and (Sr,Ba)2SiO4:Eu, and their spectroscopic properties were analyzed as a function of temperature from room temperature to 80℃. The asymmetric double sigmoidal function was applied to both blue and yellow peaks of the emitting spectrum to obtain the center wavelength, the amplitude, the half width, and the skewness parameters. According to this analysis, the center wavelength of the blue peak shifted to longer wavelength while that of the yellow peak shifted to shorter wavelength. In addition, some of the skewness parameters were found to increase upon heating, which indicates that spectrum asymmetry becomes enhanced at higher temperatures. The changes in the color coordinates and the luminous efficacy were larger for the case of silicate-based white LED. These results suggest that the silicate-based white LED is inferior to the YAG-based white LED from the viewpoint of color stability, efficacy and color rendering index.