Electron–phonon effects for (X, Y) lines of H− C4v rare-earth centres in CaF2

Abstract

(X,Y) local-mode lines of H− ions in C4v centers frequently show splitting into two or more components. These are attributed to the electron-phonon interaction between the rare-earth electronic ground states and the H− local modes. Of the non-Kramers rare-earth ions, Pr3+ has a doublet ground state and up to four (X,Y) components appear. For Ho3+, there is a low-lying first excited singlet state 1.2 cm−1 above the singlet ground state and (X,Y) components appear for each of these states. The vibronic nature of these (X,Y) local-modes is confirmed by their Zeeman spectroscopy. For Ho3+, both the nuclear-hyperfine and the electron-phonon interaction are needed to account for the Zeeman spectra of the (X,Y) lines.