Abstract
In this study, we have demonstrated that a Three-band LED in which the phosphorescence from red- and green- phosphors are mixed with a blue LED is an effective way to generate white color with a high color-rendering-index. However, in previous studies, it has been shown that the color performance is not stable at various drive currents in this type of structure. This problem is believed to result from a low extraction efficiency of the red phosphorescence. In the present study, we have demonstrated the phosphorescence extraction can be improved effectively in a three-band white LED by using a new phosphor configuration, “Multi-Layer Remote Phosphor”. This novel phosphor configuration is found to be particularly useful for improving the extraction of red phosphorescence. For the white light applications, our study further shows that an improvement of the luminous efficiency by about 95%, using a “Multi-Layer Remote Phosphor” configuration in three-band LEDs as compared with those found in a traditional “Proximate Phosphors” configuration. In these studies, the correlated color temperatures are maintained between 3800K and 5900K. In the color stability, the color differences in a “Multi-Layer Remote Phosphor” configuration are measured to be about 0.006 when the operating currents varies from 50 mA to 400 mA.; a reduction by a factor of 5 as compared with that found in the traditional phosphor packaging configuration for a three-band white LEDs.