Thermally Assisted Tunneling: An Alternative Model for the Thermoluminescence Process in Calcite

Abstract

In this work we investigate the effect of gamma and ultraviolet radiations on the thermoluminescence of Brazilian calcite. The irradiated samples presented three TL peaks at 150, 245 and 320^oC (at a linear heating rate of 1.8^oC/s), with a main emission band centered at 615nm due to the ^4G \to ^6S transition of the Mn^{2+}. The irradiated samples presented, besides the Mn^{2+} signals, three lines related related to carbonate groups. The thermal treatment and the irradiation effects on the ESR signal lead to the conclusion that (CO_3)^{3-}, stabilized in two different symmetries, and the (CO_2)^{-} ions are the electron trapping centers. It was found that the TL peaks follows a t^{-1} decay as a function of the UV illumination time. An alternative model for the TL emission of calcite is discussed, considering that the recombination of charges is processed via a thermally assisted tunnelling mechanism.