Some colour centre phenomena in ac field treated LiF single crystals later irradiated with X-rays

Optical absorption at room temperature in the wavelength region 200 nm to 650 nm of LiF single crystals under various conditions, has been studied. The conditions are: (i)as-cleaved, (ii)quenched, (iii)quenched and subjected to different high ac fields, and (iv)the field-treated samples later irradiated with X-rays. Partial thermal bleaching characteristics of the colour centres in quenched LiF subjected to ac field (5 x 104 V/cm) and later irradiated with X-rays for one hr and also the thermoluminescence (TL) of these samples have been studied. The absorption coefficient(α) of as-cleaved LiF has low values even in the low wavelength region (α at 200 nm is 1.5 cm-1); the absorption in the low wavelength region is found to increase with quenching and ac field treatment; values being largest for a quenched sample field treated at 5 x 104 V/cm. X-ray irradiation of these crystals produces two absorption bands with peaks 250 nm and 448 nm (F- and M-bands respectively), the absorption in these bands is increasing with the ac field. The thermoluminescence output exhibits two glow peaks at 200oC and 298oC; the TL output is found to enhance with ac field treatment of the samples. An attempt is made to correlate the optical absorption data with the thermoluminescence output. (author). 12 refs., 4 figs