Effects of doping concentration on thermal activation energy of trap centers in irradiated LiF:Mg2+ single crystals

Optical absorption as well as thermoluminescence emission of LiF: Mg2+ single crystals have been measured before and after exposed to gamma radiation from Co-60 source. Result of DFT calculations for pure bulk LiF indicates a large reduction in band gap energy of the crystal after doping with Mg2+ ions. As impurity concentration of Mg2+ ions in LiF is increased, the activation energy of 225 and 313 nm trap centers increases linearly with almost same slope. However, the activation energy of trap centers absorbing at 250 nm remains nearly unchanged as doping concentration increased, indicating that these trap sites are independent of Mg2+ ions. Values of average experimental activation energy (E-exp) for trap centers absorbing at 250, 225 and 313 nm for temperature range of 300-573 K have been obtained as 0.33 +/- 0.030, 0.21 +/- 0.012 and 0.16 +/- 0.013 eV, respectively.