Abstract
ABSTRACT Thermoluminescence (TL ) and X-ray excited optical luminescence (XEOL) of zirconia (ZrO2) undoped and doped with impurities of ZnO and Er2O3 have been investigated. The experimental results show that the undoped ZrO2 has the main TL peak at 98℃ and a small TL peak at around 205℃, irradiated by the UV and soft X-ray. Doping ZnO in ZrO2 sample would increase both TL peaks. However, doping Er2O3 in ZrO2 sample would decrease the 98℃ main TL peak and creates a new TL peak at 135℃. By applying the initial rise method, the activation energies for de-trapping on 98, 135 and 205℃ TL peaks were obtained as 0.90, 0.96 and 0.99 eV, respectively. The origin of the trapping centers related with 98, 135℃ TL peaks of ZrO2 are explained as from an Zr ion and an oxygen vacancy, and the 205℃ TL peak is explained as from a Zr ion and a defect complex. TL intensities of ZrO2 response to the photon energy between 2.5 to 9 keV increase linearly as a function of irradiated photon energy for ZrO2:Zn and ZrO2 sample. A simple phenomenological model is adopted to explain the mechanism of TL in the soft X-ray range. For studying the TL dose responses of ZrO2 and ZrO2:Zn induced by soft X-ray, the shallow traps of ZrO2:Zn, ZrO2 and deep trap in ZrO2 all indicate that no competing trap is observed in these traps. However, the deep trap at 215℃ TL peak in ZrO2:Zn sample can be explained as may be due to competition trap during excitation and during heating mixed, when the samples irradiated with 2.5 keV photon. But when the samples irradiated with higher energy photon at 8 keV, both of shallow and deep traps in ZrO2 sample approach to saturation below 7 Gy. However, doping the ZnO impurity would create the competitors in the deeper traps for both shallow and deep traps. The maximum peaks of XEOL broad spectra for ZrO2:Zn, ZrO2 and ZrO2:Er samples are the same at the wavelength of 480 nm, which is explained as the origin of the formation of XEOL is associated with an oxygen vacancy and Ti ion in an asymmetrically sevenfold coordination of ZrO2 in the monoclinic phase. The results of measuring the Zr L3-edge XANES by PLY and TEY demonstrated that ZnO or Er2O3-doped in ZrO2 makes the Zr-O coordination less or more symmetric than the undoped ZrO2, respectively. Moreover, a situation in which the samples are in the X-ray absorption leads to competitive absorption for electrons and photons from the de-excitation of a core hole.