Local transitions and charge transport in thermoluminescence of calcite

Colourless, natural calcite single crystals exhibit several distinct TL peaks following X- irradiation at room temperature. The emission spectra of all the peaks are attributed to Mn impurities. Kinetic analysis of the main peak at about 80°C discloses a continuous spectrum of traps having the same activation energy, 0.73 eV, and a distribution of frequency factors. Four additional peaks at 152, 179, 254 and 296°C were assigned activation energies of 0.92, 1.01, 1.52 and 1.70 eV, respectively. The kinetic data and the analysis of the emission spectra support Medlin's model which ascribes the 80°C peak to local transitions such as tunnelling, and the higher temperature peaks to processes which involve transport of ionic charge-carriers.