Luminescence properties of TlAlF₄ crystal

A single crystal of TlAlF₄ is grown by a self-seeded vertical Bridgman-method. The measured powder X-ray diffraction pattern is compared with the standard JCPDS pattern and found to be in good agreement. The crystal structure and cell parameters are calculated and refined by Rietveld refinement analysis. The optical absorption spectrum is measured and the characteristic spectral properties of Tl⁺ bands are studied. The temperature dependent photoluminescence (PL) excitation and emission spectra are measured in the temperature range of 10–300 K. The doublet structure of Tl⁺ ion A excitation bands (A₁, A₂) are observed and correlated with absorption bands. The excitation under both bands yields the same broad emission band in the range of 330–500 nm with the maximum peak at around 390 nm in room temperature. At low temperatures, this emission band is well resolved into two emission bands with maximum at 371 and 404 nm for separate excitations of 227 and 236 nm, respectively. The schematic configuration coordinate energy level diagram for emission of Tl⁺ ion is also proposed. Low temperature thermally stimulated luminescence (TSL) were carried out and analysed the trap depth (E) and frequency factor values. The mechanisms of the processes, responsible for the emission band and formation of defects pairs of the type of Tl⁰–V_k center have been discussed in detail manner.