Role of lanthanum in thermoluminescence properties of La2x Lu2(1-x)SiO5:Ce crystals

The influence of lanthanum content on thermally stimulated luminescence properties of La-2x Lu2(1-x)SiO5:Ce (x = 0, 0.08, 0.18 and 1.50 at.%) crystals was investigated. Trapping parameters such as electron trap depth E (t) and electron traps content n (0) were fitted with general order kinetic function. According to the results of the VUV transmittance spectra and band gap calculation which based on the density functional theory with the generalized gradient approximation of Perdew-Burke-Ernzerhof (GGA-PBE), band structure of the crystals and recombination mechanisms of released electrons were further studied. Results showed that there were mainly two kinds of electron traps, namely shallow (E (t) ae 0.2 eV) and deep (E (t) ae 1.0 eV) traps. With the increasing of La content, the concentration of deep traps was obviously depressed, and the depth of deep traps decreased at the same time, which was explained by suggesting the downward shift of the bottom of conduction band.