Mechanoluminescence studies of gamma irradiated sodium chloride single crystals and microcrystalline powder doped with terbium

This paper reports the mechanoluminescence (ML) induced by impulsive excitation of γ - irradiated terbium doped NaCl single crystals and powder. The NaCl crystals having different concentrations of terbium were prepared by melt technique (slow cooling). The crystals of small sizes were cleaved from grown crystal block and crushed to obtain powder or microcrystalline powder. The annealed samples were irradiated by gamma source with dose rate of 0.50kGy/hrs. Mechanoluminescence is excited impulsively by dropping a load of 0.4 kg with impact velocity 313 cm/Sec on to it. Two peaks are observed in the ML intensity versus time curves for both single crystals and powder samples. In the ML spectra a broad band with single peak at 539 nm is obtained due to transition of Tb ions from ⁵D₄ → ⁷F₅ transitions. The ML intensity of powder sample is less as compared to crystal sample of same mass. The ML intensity of microcrystalline powder increases with particle size. (author)