Effect of gallium ion content on thermal stability and reliability of YAG: Ce phosphor films for white LEDs

Y-2.94(Al1-xGax)(5)O-12:0.06Ce (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphors were prepared by conventional solid-state reaction. Phosphor films are prepared from the synthesized Y-2.94(Al1-xGax)(5)O-12:0.06Ce phosphors by a simple spin coating method. The influence of different content of Ga3+ doping on the photoluminescence (PL) spectra, thermal stability and reliability of prepared Y-2.94(Al1-xGax)(5)O-12:0.06Ce (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphor films were investigated. The emission peak of the Y-2.94(Al1-xGax)(5)O-12:0.06Ce (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphor films shifted from 545 nm to 520 nm with the Ga3+ content(i.e. the value of x) increasing from 0.05 to 0.3 excited at 460 nm. The phosphor films have excellent thermal stability, and the intensities of PL spectra decrease by about 2%, 5%, 20% and 50% at 373 K, 423 K, 473 K and 523 K, respectively. The xenon lamp aging test show that the relative PL spectra intensity of the phosphor films decreases to 95.55%, 96.24%, 96.05%, 97.67%, 95.96% and 93.22% with the x value is 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 after the xenon lamp aging test for 168 h. The high temperature and high humidity test show that the relative PL spectra intensity of the phosphor films decreases to 94.36%, 95.6%, 95.26%, 96.87%, 95.28% and 93.1% with the x value is 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 after the condition of 85 degrees C/RH85% for 168 h. The thermal cycling test show that the relative PL spectra intensity of the phosphor films decreases to 90.6%, 91.4%, 93.76%, 94.38%, 91.84% and 88.81% with the x value is 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 after the condition of 120 degrees C for 1 h and 40 degrees C for 1 h by turns for eight times. So, it can be generalized that low level of Ga3+ doping can enhance the thermal stability and reliability of Y-2.94(Al1-xGax)(5)O-12:0.06Ce phosphor films.