Effects of phosphor dispersion on optical characteristics of LED Chip Scale Package LEDs

Abstract

As being used in a phosphor converted white LED (pc-white LED), the phosphor powders are always mixed with silicone for the color conversion of LED blue chip. Therefore, phosphor dispersion in the phosphor/silicone composite is regarded as a critical factor for optical characteristics of pc-white LEDs. In this paper, effects of the phosphor dispersion on the spectra, luminous efficacies and color coordinates of the pc-white LEDs are investigated from experimental measurements of a number of Chip Scale Package (CSP) LEDs with different phosphor dispersion tragedies. The measurement results indicate that the spectra become not significantly varied when the phosphor concentration above the chip goes up to a threshold, e.g. 12%. Moreover, both the luminous efficacy and one of color coordinates u' of the CSP samples slightly increase and then reach a convergence by shifting more phosphor from the area around the chip to the area above the chip. Whereas, the color coordinate v' remains more or less the same. This work is meaningful in the following two aspects: on one hand, it gives a new perspective on the effects of phosphor dispersion on the optical characteristics of pc-white LEDs; on the other hand, it provides a new design guiding rule for those pc-white LEDs with typical spectra.