2.5eV in another paper [21]. The similarity is that the charge transfer emission from the O 2p to Ta 5d does not appear in both cases. It is quenched by Gd3þ in GTO while in KTaO3 the charge transfer band is higher than the band gap (3.7eV). Therefore, the luminescence of GTO is believed to be related to anion groups, namely TaO3 4 group, which also supports the above analysis.
5. Conclusions
In summary, we revealed the detailed temperature-dependent luminescent characteristics of GTO crystal. The spectra consist of two bands, 2.2eV band and 2.7eV band from 8K to 300K. The temperature-dependentPLintensityof thesetwobandsindicatesthe existence of thermal activation process. The activation energy of 2.2eV band and 2.7eV band is determined to be 156meV and 175meV, respectively. The lifetime of 2.7eV band is found to be muchlongerthanthatof 2.2eVbandatlowtemperature.Basedon the above, these two bands are believed to be from different luminescent centers. Besides, the annealing atmosphere exerts little influence on the PL intensity. We tentatively assign the high-energy band to self-trapped excitons (STE) localized at TaO3 4 groups and the low-energy band to relaxed excitons related to lattice imperfections. These results will be helpful to reveal the nature of scintillation mechanism of GTO crystal. However, there still exists many unknown aspects regarding the scintillation mechanism. Further- more, more accurate temperature-dependent time-resolved lumi- nescence measurements need to be performed to model the complicated radiation process. Our further study will focus on them