Correlation between thermoluminescence and mechanoluminescence of γ-ray-irradiated Dy-doped BaB4O7 phosphors

Undoped and dysprosium (Dy)-doped BaB4O7 phosphors have been synthesised by solid-state diffusion technique and its thermoluminescence (TL) and mechanoluminescence (ML) has been studied. A single peak at 162 °C along with two shoulders around 242 and 294 °C was observed in TL glow curve of undoped BaB4O7 phosphors. TL intensity increased with increasing dopant concentration and broad band was observed for the sample having 0.5 mol% of dopant concentrations. For higher concentration of dopant, concentration quenching occurred. ML has been excited impulsively by dropping a piston of mass 0.6 kg on the phosphors with various impact velocities. As the piston was dropped on to the sample, ML intensity initially increased with time attained an optimum value for a particular time then decreased and finally disappeared. ML intensity varied with dopant concentration and it has been obtained optimum for the sample having 0.5 mol% of dopant. TL and ML intensity increased with gamma doses given to the sample. ML intensity increased almost linearly with the impact velocity of the piston dropped on to the sample, however, time corresponding to ML peak shifted towards shorter time value with increasing impact velocity of the piston dropped on to it. ML emission spectrum showed characteristic emission of Dy3+ ions. In order to study the influence of deformation on TL, TL was recorded after deforming the sample by dropping the load on to it. When the TL was recorded after deforming the sample, it is found that TL yield decreased markedly and it further decreased with increasing the height of the piston from which it was dropped. Results suggest that though the mode of excitation is different in these two phenomena but similar states are responsible for TL and ML.