EMISSION OF OCTAHEDRALLY COORDINATED MN3+ IN GARNETS

The optical transitions of the octahedrally coordinated Mn3+ ion (3d(4 ) configuration) were investigated in a variety of garnet crystals. Th e spectra reveal a large Jahn-Teller stabilization energy of about 190 0 cm(-1) in the SE ground state and smaller stabilization energies of about 325 and 180 cm(-1) for the T-5(2) and T-1(2) excited states, res pectively. The observed emission intensities and lifetimes exhibit a s trong temperature dependence caused by the thermal coupling between th e energy levels as well as the temperature dependence of the radiative rate and the nonradiative rates due to coupling of odd-parity and tot ally-symmetric phonons. At 12 K, the emission lifetime is about 6 ms f or all crystals, while at room temperature it is 1.1 ms for Mn3+:Y3Al5 O12 and < 0.5 mu s for Mn3+:Gd3Sc2Ga3O12. The pure radiative lifetimes of the T-1(2) and T-5(2) levels are determined to be 6 ms and 16 mu s , respectively. The quenching process is stronger in crystals with low er crystal fields, because of the smaller energy gap between the T-5(2 ) and T-3(1) levels and the higher population of the T-5(2) level. (C) 1998 Elsevier Science B.V. All rights reserved.