Abstract: Gd doped lead fluoride crystals were grown by modified Bridgman methods. Under X-ray excitation, their emission intensities peaked at 278nm and 312nm 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 PbF_2 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

Key words: PbF₂ crystals, Gd ions, luminescence intensity, non-uniformity