Crystal field effects on the thermoluminescence of manganese in carbonate lattices

Thermoluminescence emission spectra are reported for a wide range of carbonates. All the samples show Mn luminescence centres and the spectra variously include narrow band features, when the Mn is in low concentration, or broad emission bands at high concentrations. The form of the spectra change with temperature, and for some Mn concentrations, alter from broad to narrow band spectra with increasing temperature. In calcite there is concentration quenching of the luminescence when the Mn impurity levels exceed similar to 1000 ppm which varies with glow peak temperature. The emission wavelengths of the Mn show monotonic dependencies, in both rhombohedral and orthorhombic lattices, as a function of the length of the metal to oxygen bonds in the various minerals, and the presence of Mn in alternative sites is revealed for dolomite. The detailed line spectra can be related to the Mn ion energy level diagram, as perturbed by the crystal field term, which for emission in rhombohedral calcite has a value of similar to 1000 cm(-1), but for orthorhombic sites in aragonite is similar to 1200 cm(-1). Copyright (C) 1996 Elsevier Science Ltd