Abstract
Ti4+ activated zirconia (ZrO2) has been known as a phosphor, which has a broad emission band peaking at 490nm and an afterglow lasting for several minutes. The visually detectable emission due to afterglow would be much improved by means of increasing a fluorescent intensity or forming traps that have suitable depth below a conduction band of ZrO2. We first examined the dependence of the luminescent intensity on coordination number for luminescent centers in three phases and temperature prepared phosphors. 0.1% Ti4+ activated monoclinic ZrO2 has the highest emission intensity as compared to SrZrO3:0.1%Ti and tetragonal ZrO2:20%Y2O3, 0.1%Ti. The coordination number of Ti4+ in a monoclinic ZrO2 is 7. Above the calcination temperature of 1200°C, luminescent intensity of the monoclinic ZrO2 phosphor sharply increased through phase transition. It was also observed that the persistence of afterglow depended upon the concentration of the traps created at high temperature. The traps were investigated by measuring thermoluminescence spectra. We discuss a mechanism of afterglow for the monoclinic ZrO2 phosphor. On the basis of these results, we tried to synthesize Ti4+ activated hafnia (HfO2), and measured luminescent properties.
