The luminescence decay-time of Mn2+ activated calcite

Luminescence decay time data are presented for 17 samples of synthetic calcite and a natural calcite between room temperature and approximately 15 K. The majority of the samples have Mn concentration in the range 0.0001–0.01 atoms per formula unit (apfu). Their spectra are consistent with a single exponential decay. It was necessary to use a “stretched” exponential to obtain adequate fits to the spectra of two samples having Mn concentrations of 0.036 and 0.091 apfu. The decay time at room temperature ranges from approximately 40–57 ms. At low temperature the corresponding range is 51–120 ms, indicating that thermal quenching of the decay time takes place. The decay time is dependent on the concentration of Mn, reaching a maximum (at both room- and low-temperature) in the range 0.001–0.003 apfu. The composition dependence is greater at low temperature. The results are discussed in terms of the Mott-Seitz and multiphonon mechanisms of thermal quenching. It is concluded that the latter provides a better fit to the data and is more consistent with models of the luminescence process in calcite:Mn.