Mechanoluminescence and thermoluminesence in γ-irradiated rare earth doped crystals

Mechanoluminescence (ML) and Thermoluminescence (TL) in γ-irradiated Dy, Ce, Er and Gd doped CaF2 crystals were studied. The crystals of doped CaF2 were grown by the Bridgman technique. The cleaved crystals were annealed at 450 ∘C for about two hours and cooled very slowly and then irradiated for different time from 60Co source having an exposure rate of 2.8×103 Gy/hr. ML was excited by applying uniaxial pressure on to the samples. Both the ML and TL intensities of CaF2 crystals increase with doping of rare earth impurities. Both the ML and TL intensity of γ-irradiated Dy, Ce, Er and Gd doped CaF2 crystals initially increase with increasing concentration of dopants obtaining an optimum value at 0.1 mole% level then further decreases with increasing dopant concentration. ML and TL intensity of γ-irradiated Dy, Ce, Er and Gd doped CaF2 crystals initially increases with the irradiation dose and then saturates at higher values of γ-doses. The order of ML and TL intensity for dopants were found similar and their order for decreasing intensity is CaF2:Dy>CaF2:Ce>CaF2:Er>CaF2:Gd. The ML spectra are almost similar to the TL spectra, this suggest that the centres emitting TL and ML may be the same although different processes cause their excitations.