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

Abstract

Rare earth ions play an important role in modern technology as optically active elements in solid-state luminescent materials. In many of these materials, interactions between the electronic band states of the host crystal and the rare earth ion’s localized 4f^N and 4f^N-1 5d states influence the optical properties of materials. This paper reports the mechanoluminescence (ML) induced by impulsive excitation and thermoluminescence (TL) of γ-irradiated dysprosium doped NaCl single crystals and powder. The NaCl crystals having different concentrations of dysprosium were prepared by melt technique (slow cooling).The crystals of small sizes were cleaved from grown crystal block and crushed to obtain microcrystalline powder. The annealed samples were irradiated by gamma source with dose rate of 0.50 kGy/h. Mechanoluminescence is excited impulsively by dropping a load of 0.4 kg with impact velocity 313 cm/s onto it. Two peaks are observed in the ML intensity versus time curves for both single crystals and powder samples. In thermoluminescence of NaCl: Dy crystals and powder samples only one peak is observed in the glow curve at around 210-230°C. In the ML spectra, a broad band with single peak at 482 nm is obtained. The ML and TL intensities of single crystals are compared with the microcrystalline powder of the same mass in the present investigation. The total TL intensity obtained is more in microcrystalline powder than single crystal and reverse intensity yield is obtained in the ML process.