Tunneling processes in afterglow of calcite

A study of thermoluminescence and isothermal decay of calcite synthetic single crystals after electronic irradiation shows that a new, weak, low temperature emission precedes the “360 K” glow peak (related with manganese): it has the same emission spectrum as the glow peak, the intensity varies in inverse proportion to the time and does not depend on temperature in a wide range (LNT to 180 K). These two emissions are accounted for by a model with charge transfer taking place between traps and manganese centers through two competing tunneling processes. One starts from the fundamental level of the traps and is athermal. The other starting from a thermally excited level 0.62 eV higher, gives rises to the 360 K glow peak.