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.