Two-photon vibronic transitions of Gd3+ in cubic Cs2NaGdCl6 crystal

Two-photon absorption spectroscopy was applied for investigation of vibronic transitions accompanying the 8S72 → 6P72 and 6P52 transitions of Gd3+ in the cubic elpasolite Cs2NaGdCl6. It was found that the vibronic transitions accompanying the zero-phonon lines were associated with the even modes for the 6P72 term and with the odd modes for the 6P52 term. The mechanism of two-photon f-f vibronic transitions responsible for such behaviour was discussed.