Effect of phosphor composition and packaging structure of flexible phosphor films on performance of white LEDs

Abstract

YAG:Ce³⁺ phosphor and CASN:Eu²⁺ phosphor were synthesized by conventional solid-state reaction, and the phosphor films were prepared from the synthesized YAG:Ce³⁺ phosphor and CASN:Eu²⁺ phosphor by a simple spin coating method. The influence on the concentration of the red phosphor and the different packaging structure of the phosphor films on the optical and electrical properties of white LEDs were investigated. The red and green phosphor were coated layer by layer to investigate the spectral absorption effect of phosphors in the films. The phosphor film placing green phosphor adjacent to the chips is named as G–R structure, likewise, the red phosphor close to the chips is labeled as R–G structure. The results show that the emission spectra of the phosphor films with G–R structure exhibit obvious red shift with the increase of the proportions of red phosphor due to the red phosphor have a reabsorption effect on the green light. Then, the phosphor films with G–R and R–G structures were packaged on the LED respectively, and the light efficiency and the correlated color temperature (CCT) of the LEDs gradually decrease with the increase of the proportions of red phosphor. The luminous efficacy of LEDs packaged by G–R structured phosphor film is higher than that of LEDs packaged by R–G structured phosphor film. The luminous efficiency of LEDs packaged by G–R structured phosphor film can reach 128.95 lm/W, the CCT is 4458 K, and the CRI is 65.1. Moreover, the CCT uniformity of LEDs packaged by G–R structured phosphor film is superior to that of LEDs packaged by R–G structured phosphor film. Therefore, the G–R structured phosphor film has potential application values for improving the luminous efficiency and light uniformity of the device.