PbF_2:Gd晶体的发光强度与发光均匀性研究

以Ｘ射线荧光光谱分析为手段，测试了用Ｂｒｉｄｇｍａｎ方法生长的ＰｂＦ２：Ｇｄ晶体中Ｇｄ离子沿生长方向的分布．发现该晶体在Ｘ射线激发下的发光强度与Ｇｄ在ＰｂＦ２晶体中的含量变化均从结晶开始端至结晶结束端逐渐降低，表明ＰｂＦ２：Ｇｄ晶体的发光是不均匀的，这种不均匀性源于Ｇｄ离子在ＰｂＦ２晶体中的分布不均匀性．通过在ＰｂＦ２：Ｇｄ晶体中掺入一定量的碱金属离子，可以比较有效地改善Ｇｄ离子在ＰｂＦ２晶体中的不均匀分布，使晶体的发光均匀性和透光率得到明显提高，其中以Ｎａ离子的均匀化效果为最好．推测Ｎａ离子的作用是消除了ＰｂＦ２：Ｇｄ晶体中因Ｇｄ离子的掺杂而造成的间隙Ｆ离子，从而使晶体中的缺陷浓度大大降低．

Luminescence intensity and Uniformity of PbF_2:Gd Crystals

Gd doped lead fluoride crystals were grown by modified Bridgman methods. Under X-ray excitation, their emission intensities peaked at 278urn and 312urn increase with the doping amount of Gd3 ions, but decrease from the beginning part to the finishing end of the crystallization along the growth direction. The concentration of Gd3 ions in the PbF2 crystal, analyzed by X--ray fluorescence spectrophotometer, also decreases in the same direction as emission intensity does. The correspondence between Gd content and luminescence intensity of PbF2:Gd crystal demonstrates that the non-uniformity of luminescence intensity results from the in-homogeneous distribution of Gd3 ions in the crystal. It was found that by co-doping suitable amount of alkali metal ions, such as Na and K , with Gd ion into PbF2 crystal, the difference of luminescent intensities and Gd3 concentration from the bottom to the top of the crystal become smaller and the transmittance is higher than that of the single doping crystal. Especially, the uniformization effect of Na ions is better than that of K ions. It shows that the role of Na in the PbF2:Gd crystal is eliminating the interstitial fluorine ions formed by the doping of Gd3 ions and so decreasing point defect content in the crystal.