Studies of swift heavy ion induced colour centres in LIF thin films deposited on silica substrates

Swift heavy ion induced colour centres in polycrystalline LiF thin films deposited on silica substrate were studied. LiF thin films of 200 nm thickness, deposited by the electron beam evaporation method, and silica substrates were irradiated with 120MeV Au9+ ions in the fluence range 5 x 10(10) - 1 x 10(13) ions cm(-2). Optical absorption, photoluminescence (PL) and glancing angle x-ray diffraction (GAXRD) techniques were used for the characterization of the irradiated films. Optical absorption spectroscopy was performed on irradiated LiF films by using irradiated silica substrates as reference sample. The resulting spectra show three bands at 260 nm, 380 nm and 445 nm corresponding to F, F-3 and F-2 colour centres, respectively. Absorbance of colour centres increases with fluence and seems to saturate at higher fluences. PL spectra, performed by an excitation source of 442 nm, show two broad bands of F-2 and F-3(+) colour centres. The intensity of both the centres increases upto 3 x 10(11) ions cm(-2) followed by some decrease. The GAXRD results show that the average grain size decreases systematically from 35 nm for the pristine film to 20 nm for the sample irradiated at a fluence of 1 x 10(13) ions cm(-2).