Photoluminescence and Photocatalysis Properties of Dual-Functional Eu3+-Doped Anatase Nanocrystals

Red-color-emitting TiO2:Eu3+ nanophosphors have been synthesized through the hydrothermal process. Samples with different morphologies have been obtained by changing pH values of solution. The structural and luminescence properties of samples were investigated through scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-vis spectra, and photoluminescence (PL) spectra. Most importantly, surface photovoltage spectra were used to discuss the charge transfer process and further explained the luminescence phenomenon of different morphologies for the first time. The critical transfer distance for the Eu3+ ions in TiO2 matrix was calculated, and we could conclude that the concentration quenching process was attributed to the multipole-multipole interaction. The relative intensity ratios of D-5(0)-F-7(2) transition to D-5(0)-F-7(1), transition of TiO2:x%Eu3+ (x = 2, 4, 6, 8, 10, 12) have been calculated to understand the lattice symmetry and coordination environment of Eu3+ ions. The spectral characteristics and site symmetry have been discussed through the Judd-Ofelt parameters. Moreover, the investigation of photocatalytic ability of TiO2:x%Eu3+ showed that the photodegradation efficiencies decrease with an increase in the amount of Eu3+ for the degradation of methyl orange under white light irradiation, and the photodegradation efficiency of TiO2:2%Eu3+ was 99% after 25 min, which is much more higher than that for TiO2:12%Eu3+ (25%).