One- and two-photon spectroscopy of the 3E g state of NaF:Cu+: Observation and analysis of vibronic fine structure

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Abstract
One‐ and two‐photon laser excitation spectra of the 1A1g→3Eg transition of NaF:Cu+ are reported, these being the first direct observations of the lowest d9s excited state of Cu+ in an alkali halide host. The spin–orbit splitting of the 3Eg vibronic origin is directly measured, and can be compared with values inferred from studies of the temperature and magnetic field dependence of the emission lifetime. Clear vibrational progressions based on both spin–orbit origins are assigned to odd parity local modes of t1u symmetry. We also report high resolution emission spectra which reveal evidence of a corresponding local mode in the ground state with a fundamental frequency significantly higher than that observed in any of the d9s excited states. We model these spectroscopic data and those of the 1Eg and 1T2g states within the adiabatic approximation using three‐parameter anharmonic vibrational potentials, evaluating the energies and wave functions by a variational procedure. Good fits are obtained for most spectroscopic features. Those features which are not accommodated by the adiabatic model potentials are accounted for by nonadiabatic vibronic coupling.