Selective excitation and analysis of NaF:Cu+ electronic transitions using two-color, two-photon spectroscopy

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Abstract
Nonresonant, one‐color and two‐color, two‐photon excitation spectra of d10→d9s transitions in NaF:Cu+ at TT2g(3T2g) and Eg(3T2g) electronic states within the d9s excited state manifold. Vibronic fine structure is observed at the electronic origins of transitions to each of these states. This structure aids in band assignment and in analysis of the symmetric mode vibrational potentials in the excited states. Band intensities are analyzed and vibronic fine‐structure linewidths are interpreted in terms of nonradiative relaxation. These new data require a reassessment of the assignment of the bands previously attributed entirely to transitions to the 1Eg state. It is suggested that Jahn–Teller splitting does not distort this state to a spectroscopically observable degree, contrary to earlier interpretations of the spectra, and that only the lower energy of the two Eg bands originates from transitions to the state ofprimarily singlet character. Observed spin–orbit coupled energy levels are modeled using crystal field splittings, singlet–triplet splittings, and the Cu+3d spin–orbit constant as variable parameters. The resulting fit gives energies and intensities which are in agreement with all measured experimental values if ζ3d is approximately equal to its free ion value.