The visible luminescent characteristics of ZnO supported on SiO2 powder

In situ laser-induced luminescence spectroscopy is used to study the visible luminescent characteristics of ZnO during the preparation process of ZnO supported on SiO2 by the pyrolysis of different Zn precursors in N-2 or O-2 atmosphere. The excitation source is 325 nm light, which is above the band gap (3.37 eV) of ZnO. In N-2 atmosphere, it is shown that green ( centered at ca. 520 nm), yellow ( centered at ca. 580 nm) and orange ( centered at ca. 640 nm) luminescence bands appear for ZnO produced from zinc acetate, zinc hydroxide and zinc nitrate, respectively. After these samples are treated by O2, green band is changed into yellow band and yellow band is changed into orange band. On the other hand, it is also found that the laser irradiation on the sample could alter the luminescent behavior of ZnO produced at the beginning decomposition temperature of the Zn precursors. While this sample is irradiated, the orange band is gradually changed to a yellow band, the luminescent intensity finally increases more than 30 times that at the beginning of irradiation. However, irradiation hardly affects the luminescent properties of ZnO after calcination above 160 degreesC. The results indicate that the visible luminescence from ZnO is associated with the oxygen vacancies in ZnO, and the electronic state levels responsible for the visible luminescence bands are changing with the density of oxygen vacancies in ZnO. The green, yellow and orange bands are ascribed to the state of ZnO with high density of oxygen vacancies, with moderate density of oxygen vacancies and with less oxygen vacancies, respectively