SPECTROSCOPIC PROPERTIES OF CO2+ IONS IN MGAL2O4 SPINELS

The absorption, excitation, and luminescence spectra of MgAl2O4:Co2+ are studied. The spectra are measured at temperatures from 4.2 to 300 K. From the low temperature absorption spectra the Racah parameters and energy level assignments are derived. Three emission bands are found, one in the visible and two in the infrared region. The visible one is assigned to the 4T1(4P) --> 4A2 transition. In the infrared the 4T1(4P) --> 4T2 and 4T1(4P) --> 4T1(4F) transitions are observed. It is shown that the luminescence originates from different Co2+ sites situated in a weak ligand field. The luminescence decay curves are measured in a wide range of temperatures (from 4.2 to 300 K) and found to be non-exponential. The temperature dependence of luminescence and the mechanism of non-radiative deactivation of the 4T1(4P) level is briefly discussed.