Preparation and luminescent properties of MO₂ (M=Zr, Hf) with Baddeleyite structure

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.