Two-photon excitations ofAg−centers in RbBr

Two-photon studies of the excitation of the ${\mathrm{Ag}}^{\mathrm{\ensuremath{-}}}$ center in RbBr as a function of the polarization of the excitation light are reported. An intense band excited at 4.38 eV could be assigned to the two-photon allowed transition $^{1}\mathrm{A}_{1\mathrm{g}}$${\ensuremath{\rightarrow}}^{1}$${\mathrm{A}}_{1\mathrm{g}}$. On the low-energy tail of this band a weak excitation of the two-photon forbidden transition $^{1}\mathrm{A}_{1\mathrm{g}}$${\ensuremath{\rightarrow}}^{1}$${\mathrm{T}}_{1\mathrm{u}}$ (C band) was also observed. A proper choice of the polarization state of the excitation light allowed us to detect a double band at energies close to the $^{1}\mathrm{A}_{1\mathrm{g}}$${\ensuremath{\rightarrow}}^{1}$${\mathrm{A}}_{1\mathrm{g}}$ excitation. The corresponding excited states are of $^{1}\mathrm{E}_{\mathrm{g}}$ symmetry and are interpreted as the Jahn-Teller split $^{1}\mathrm{E}_{\mathrm{g}}$ ${(}^{1}$${\mathrm{D}}_{2}$) state.