不同气氛退火对PbWO4单晶发光的影响

通过对不同气氛条件下退火的PbWO4(PWO)单晶样品的激发谱与发射谱的对双研究，发现真空退火从整体上抑制PbWO4的发光强度，氧空位（Vo）缺陷是420nm吸收和红光发射的原因，而空气退火可以有效抑制Vo缺陷，全面改善PWO的发光性能。另外，首次报道了310nm附近的激子激发峰发生劈裂的现象，其中波长较长的320nm激发对应于与Vo缺陷相关的激子激发态。

Influence of Different Annealing Atmosphere on the Luminescence of PbWO4 Single Crystal

The influence of different annealing atmospheres (vacuum, air, reductive) on the luminescent properties of lead tungstate single crystals (PWO) has been investigated. UV-excited emission spectra and their excitation spectra of the same PWO sample at different annealing conditions were reported. The emission of PWO as grown was weak and dominated by the defect-related red band which is a disadvantage for the scintillation of PWO. The intrinsic blue band was just discernable from the red band. After air annealing, the luminescence intensity was increased enormously and the green band was turn into the prominence of the emission spectra. It suggested that the green emission originate from some local excess oxygen defects, such as (WO_4~(2-)+Oi) centers (here Oi means interstitial oxygen atom). After subsequently vacuum annealing, the emission intensity was dropped again, and the increase of 420nm excitation in the excitation spectra of the red band emission was remarkable. The color center around 420nm is harmful to the radiation hardness of PWO and should be avoid. It suggested all the unfavorable factor after vacuum annealing is caused by the increase of the concentration of oxygen vacancy Vo since the oxygen in the lattice can diffuse outward through the surface when annealing in vacuum under high temperature. So air annealing which decrease the concentration of Vo is a good method to improve the luminescence properties in full scale.In addition, the splitting of 310nm excitation band into two sharp excitation peaks around 305nm and 320nm was observed for the first time when another PWO sample was investigated after vacuum annealing. With the increasing of Vo concentration, 305nm peak lowered while 320nm peak heightened. It suggested that 305nm excitation is corresponding to the excitation of intrinsic excitons while 320nm excitation is corresponding to the bound exciton related to Vo-defects.