We investigated the effects of the SiO2 surface coating on the optical properties of Sr2MgSi2O7:Eu+ phosphor which is used for a white light source in the blue LED chip. A modified sol-gel method was used for the surface coating of the commercial yellow phosphor with SiO2. The experimental results suggest that the surface coating of phosphors with SiO2 nano-particles leads to an increase in the intensity of the 550 nm peak. It is of interest that this increasing tendency depends on the concentrations of the colloidal solution. Thus, the surface coating of phosphors is a way for improving the luminance of the white LED.