Even-parity excited states of Ag-centers in alkali halides

Two-photon excitation of the Ag- centers in RbCl, RbBr, and KCl have been measured. From the dependence of luminescence on the polarization of the exciting beams, the symmetry of the final levels could be obtained. In all three host crystals, we observed an intense band assigned to the 1A1g1A1g transition. At higher energies 1A1g1Eg and 1A1g1T2g transitions could be identified but their presence and intensity change in the different crystals. On the high-energy side of the investigated range, we could observe an intense luminescence signal arising from a two-step excitation process; the exciting photon energy becoming resonant with the 3T1u state (A band). © 1991 The American Physical Society