Influence of γ Irradiation on the Optical and Energy Spectra of Fluoride Single- and Multicomponent Crystal Systems Activated by Cе3+ Ions

The scintillation properties of LiF crystals and the family of multicomponent compounds LiF–RF₃ (R = Y, Gd), activated by Ce³⁺ ions, proposed as materials sensitive to thermal neutrons and γ radiation, are compared. An abnormally large cross section of radiative capture of thermal neutrons in gadolinium and the calculated high values of the effective charge number Z of multicomponent compounds determine their efficiency as neutron and gamma scintillators in comparison with LiF. The absorption spectra of unirradiated and γ-irradiated LiF crystals activated by cerium ions are analyzed. The bands of induced color centers are identified. The conversion of the ion oxidation state, Ce⁴⁺ → Ce³⁺, related to effect of γ quanta on the crystals, is investigated. The light yield of all crystals studied was determined by comparing the positions of the maxima of total absorption peaks with the position of the maximum of the total absorption peak of a standard NaI(Tl) sample in the energy spectra from a ¹³⁷Cs γ source with an energy of 662 keV. The effect of increasing the light yield under γ irradiation of LiF crystals with Ce³⁺ ions was discovered and explained in terms of the participation of γ-induced color centers (F and F^- centers). The possibility of increasing additionally the light efficiency due to sensitized luminescence in LiGdF₄ : Ce³⁺ crystals was analyzed.