COLOR-CENTER PHENOMENA IN LASER-EXCITED LIF SINGLE-CRYSTALS IRRADIATED WITH X-RAYS

Colour centre phenomena in LiF single crystals have been studied when they are subjected to different conditions like (i) quenching, (ii) laser excitation, (iii) X-ray irradiation and (iv) a combination of them. The absorption coefficient (alpha) of as-cleaved LiF has low values in the low wavelength region (alpha at 200 nm is 1.5 cm-1), the absorption in the low wavelength region is found to increase with quenching and laser excitation. X-ray irradiation of these crystals produces two absorption bands with peaks at 250 nm and 448 nm (F- and M-bands, respectively), the absorption in these bands is increasing with the time of laser excitation. If quenched and X-ray irradiated crystals are later subjected to laser excitation, the absorption in the two bands decreases. The thermoluminescence (TL) output exhibits two glow peaks at 200 and 298-degrees-C; the TL outputs have been correlated with optical absorption data. An attempt is made to understand the defect processes that are taking place in LiF crystals.