Crystal field effects on the luminescence of manganese in carbonate lattices

Abstract

Thermoluminescence emission spectra are reported for a wide range of carbonates. All the samples show Mn luminescence centres and the spectra variously include narrow and 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 ~ 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 ~1000 cm¿1, but for orthorhombic sites in aragonite is ~1200 cm¿1.