Two-photon electronic spectroscopy of Cs2GeF6:Mn4+

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Abstract
The spectrum of the d→d transitions of Mn+4 in Cs2GeF6 has been observed by means of two‐photon spectroscopy using a tunable infrared laser. The g→g two‐photon spectrum is fully allowed and therefore, shows the true electronic origins and symmetric vibrational sidebands without any interfering odd parity vibrations. The resulting spectra for each of the four electronic states studied (2Eg,2T1g,4T2g,a 4T1g), a 4T1g), are free of lattice mode and enabling mode complications and provide data for the analysis of Jahn–Teller effects, spin‐orbit coupling, and other dynamical processes at the impurity ion. In the 4T2g, state there is clear evidence both in the quenching of the origin quartet, and in the vibronic structure for both e‐ and t2‐type Jahn–Teller distortions. Each of the four states shows a specific, and a different mode of coupling to the lattice. Many other spectroscopic details are revealed, none of which were evident in the one‐photon spectra.