Photoluminescence from Eu3+ Ions Doped in ZnO Films Sputter-Deposited with H2O Vapor Gas

We found that ZnO:Eu films sputter-deposited with H2O vapor gas produce intense photoluminescence from Eu3+ ions through excitation of ZnO host crystals with a 325-nm laser light, whereas those deposited with O-2 gas do not. At optimum annealing temperatures of 300-500 degrees C, the primary luminescence from Eu3+ ions appeared at 612 nm, which was much stronger than the near-band edge and defect emissions from ZnO. After annealing at higher temperatures, the 612-nm peak attenuated, and two emission lines at 612 and 620 nm, corresponding to two distinct chemical sites, had comparable intensities. These observations suggest that incorporating H+ and/or OH- species in ZnO crystals are prerequisite for emissions from Eu3+ ions to occur. Characterization with infrared absorption spectroscopy and X-ray diffraction suggested that Eu3+ ions substitute Zn2+ sites when OH- (H+) species are contained in ZnO crystals. The role of H+ and/or OH- species may be either charge compensation when substituting Zn2+ sites with Eu3+ ions or creation of trapping centers of excited energies that mediate efficient energy transfer from ZnO to Eu3+ ions. (C) 2013 The Japan Society of Applied Physics