Radiation Induced Optical Absorption of Cubic Lead Fluoride Crystals and the Effect of Annealing

Transparent and colorless lead fluoride crystals with sizes of 20×20×20 (mm³) are irradiated with several doses of γ-rays from a ⁶⁰Co source. Their transmittance spectra before and after irradiation are measured, and a new parameter ΔT=T_b?T_a is defined to evaluate the irradiation damage. Three optical absorption bands peaking at 270 nm, 370 nm and 500 nm are found in the plots of ΔT versus wavelength, and their intensities increase with the irradiation dose. These optical absorption bands, except the one at 270 nm, can recover spontaneously with time. Thermal annealing treatment can enhance this recovery of the transmittance, while the optimum annealing temperature for different samples depends on the irradiation dose.