Time-resolved luminescence spectra of tungstates

研究了钨酸铅（PbWO_4）在8-300 K宽温度范围内的时间分辨发光光谱。对于脉冲激发，样品被安装在真空室中，并由Q开关Nd：YAG激光器的第四谐波（266 nm）照射。在300 K下，当延迟时间从0增加到1 ms时，未掺杂样品的时间分辨发光峰位从2.88 eV移动到2.55 eV，在77 K以下的低温下没有观察到明显的移动。当延迟时间从0增加到500 μs时，峰位从2.86 eV移动到2.32 eV。在77 K时，随着延迟时间从0增加到1 ms，发光峰从2.82 eV移动到2.55 eV。在此基础上，我们强烈地认为，在2.88 eV处产生蓝色发光的自陷激子（STE）态被Jahn-Teller效应分裂成三个子能级。这与PbWO_4中的STE位于四面体（WO_4）~+离子上的事实是一致<2->的。此外，在2.32 eV处观察到的绿色发光归因于受Mo离子扰动的STE态的辐射衰减。另一方面，在未掺杂样品中在2.55 eV处观察到的蓝绿色发光归因于受晶格不完整性扰动的STE状态的辐射衰减，例如，氧缺陷

Time-resolved luminescence spectra of lead tungstate (PbWO_4) were investigated in a wide temperature range of 8-300 K. For pulsed excitation, the sample was mounted in a vacuum chamber, and was irradiated by the fourth harmonics (266 nm) of a Q-switched Nd : YAG laser. The time-resolved luminescence was observed by means of a gated ICCD camera, with spectral resolution of 10 nm.In undoped samples at 300 K, it was found that the peak position shifts from 2.88 eV to 2.55 eV when the delay time was increased from 0 to 1 ms. No appreciable shift was observed at low temperatures below 77 K.In Mo-doped samples at 300 K, it was revealed that the peak position shifts from 2.86 eV to 2.32 eV when the delay time was increased from 0 to 500 μs. At 77 K, the luminescence peak shifted from 2.82 eV to 2.55 eV with the increase of the delay time from 0 up to 1 ms.On the basis of these results, it was suggested strongly that the self-trapped exciton (STE) state responsible for the blue luminescence at 2.88 eV is slit into three sublevels by the Jahn-Teller effect. This is consistent with the well-known fact that the STE in PbWO_4 locates on the tetrahedral (WO_4)^<2-> ions. Furthermore, the green luminescence observed at 2.32 eV in Mo-doped PbWO_4 was ascribed to a radiative decay of the STE state perturbed by Mo ions. On the other hand, the blue-green luminescence observed at 2.55 eV in undoped samples was attributed to a radiative decay of the STE state perturbed by lattice imperfection, e.g., oxygen defect.