VUV-luminescence and excitation spectra of the heavy trivalent rare-earth ions in fluoride matrices

VUV 4f n → 4f n−15d transitions of Gd3+, Er3+, Tm3+, and Lu3+ in fluoride matrices have been analyzed with high-resolution luminescence and excitation spectroscopy. In trifluorides, strong electron-phonon coupling has been found. In the other matrices, the luminescence spectra clearly yield zero-phonon lines and phonon replica, indicating intermediate coupling. The energies of the zero-phonon lines observed are compared with theoretical predictions. Near the threshold of f → d excitations, some of the excitation spectra yield sharp structures which cannot be explained with phonon replica but will be discussed in terms of the energy levels of the 4f n−15d configuration.