A unique photofunction of YVO4:Bi3+,Eu3+ nanophosphor: Photoluminescent indication for photochemical decomposition of polyurethane

We have developed a transparent composite film consisting of YVO4:Bi3+,Eu3+ nanophosphor and polyurethane resin which exhibits unique photophysicochemical behavior. The nanophosphor shows red photoluminescence through f–f transitions of Eu3+ under near-UV irradiation. The emission intensity drops to half of the initial value after continuous irradiation for 23 h. As shown by electron spin resonance spectroscopy, this decrease in the emission intensity is caused by the formation of V4+ defects. In addition, thermal analysis and Fourier transform infrared spectroscopy show that the amount of the organic species in the film decreases from 58 to 25 wt% after 23 h. These results indicate that the nanophosphor promotes photooxidative decomposition of the polyurethane resin, while some of the V5+ ions in YVO4 are converted to V4+ ions by photoreduction. Prolonged irradiation for 96 h leads to complete decomposition of the polyurethane and the disappearance of the V4+ defects, resulting in the recovery of the emission intensity. These findings suggest that the photoluminescence of YVO4:Bi3+,Eu3+ nanophosphor can be used to detect the photooxidative decomposition of polyurethane.