I. Introduction
Due to extraordinary characteristics, such as energy saving, high luminous efficiency, and long life and high reliability, high-power white light-emitting diodes (LEDs) have been widely used in our daily lives [1]–[5]. Currently, most of the white LEDs are generated through the combination of the yellow phosphor and blue chip. However, because of the shortage of long-wavelength light, the light quality, particularly the color-rendering index presents poor performance.