Raman and spectroscopic studies of the early steps of crystallization in ZrF4-LaF3-AlF3-ErF3 glass

The effect of the thermal treatments at a temperatures much below the glass crystallization on the microstructure of ZrF4-based fluoride glass doped by Er3+ ions was studied. The glass characteristic temperatures and the apparent activation energy for crystallization were estimated on the basis of differential thermal experiments. The crystallization of ErxLa1-xZr3F15 phase was detected in nearly transparent samples. Room temperature, Raman scattering spectra in the acoustic and optical phonon regime as well as fluorescence of Er3+ ions in the infrared and visible region indicated a continuous structural modification of the glassy matrix during heat treatment and crystallization initiation.