Mechanoluminescence and Thermoluminesence in γ-Irradiated Rare Earth Doped CaF2 Crystals.

Mechanoluminescence (ML) and Thermoluminescence (TL) in gamma-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 degrees C for about two hours and cooled very slowly and then irradiated for different time from Co-60 source having an exposure rate of 2.8x10(3) 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 gamma-irradiated Dy, Ce, Er and Gd doped CaF2 crystals initially increase with increasing concentration of dopants obtaining an optimum value at gamma-irradiated Dy, Ce, Er and Gd doped CaF2 crystals initially increases with the irradiation dose and then gamma-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.