[Preparation and luminescence of Eu3+ /Yb3+ codoped ZrO2 powders]

Samples of Eu3+ /Yb3+ co-doped ZrO2 powders were prepared by co-precipitation method. The dependence on the sintering temperature and doping concentration of the structure and luminescence was studied. The results confirmed that the sintering temperature has significant influence on the crystalline phases of ZrO2. As the sintering temperature increased the tetragonal phase was transformed into monoclinic phase. After sintered at 1150 degrees C, single monoclinic phase was observed. In contrast, with the increase in the doping concentration of Yb3+, the crystalline phase was also changed, and the monoclinic phase was transformed back to tetragonal phase. With 1% Eu3+ and 10% Yb3+ doping, single tetragonal phase presents. It was observed that the luminescent properties of Eu3+ ions in two structures were different. Experiment results reveal that the luminescence can be affected by both sintering temperature and doping concentration. With single Yb3+ doping, no NIR emission was observed under ultraviolet light excitation (270 nm). However, with Eu3+/Yb3+ codoping, NIR emission around 980 nm from Yb3+ ((2)F(5/2)-->(2)F(7/2)) was observed under the same excitation. Furthermore, it is confirmed that Yb3+ has the same excitation spectrum with Eu3+. This down-conversion result indicates that there is an energy transfer process between Eu3+ and Yb3+. Cooperative energy transfer process and cross-relaxation process were assigned as the possible mechanism for the near-infrared emission of Yb3+.