A Raman study of the superionic behaviour of CaF₂ crystals containing trivalent lanthanide ions

Abstract

Raman scattering studies of the T 2g mode in an undoped CaF 2 crystal and in CaF 2 crystals separately doped with 10% of Tb 3+ , Tm 3+ and Nd 3+ ions as well as 10% to 20% of La 3+ ions, in the temperature range 295 K -1400 K, are presented. The linewidth (FWHM) of the T 2g peak is found to increase almost linearly with temperature, up to the transition onset temperature of ~1025 K for the undoped and between 850 K and 975 K for the 10% doped crystals. Thereafter linewidth increases are steeper in all cases. Further, as the temperature of each sample is raised, the peak position drifts to lower energies. The 15% and 20% La 3+ -doped samples show the same behaviour as for 10% except for slightly lower transition temperature and peak energy. Interstitial F -ions and lattice distortions are responsible for these effects.

Fluorescence of trivalent neodymium in various materials excited by a 785 nm laser

“…In the present work, in fluorite, the frequency of the T 2g mode is observed to decrease by 3 cm -1 (328 to 325 cm -1 ) as the temperature is raised from 77 to 294 K, yielding an average slope of 1.3×10 -2 cm -1 /K, a value compatible with that obtained by Mujaji and Comins (2007) at higher temperature. In calcite, the frequency of the external vibrational E g mode decreases by 4 cm -1 (288 to 284 cm -1 ), an amount comparable to that measured by Sood et al (1981).…”

Spectroscopy of Tm3+-doped CaF2 waveguiding thin films grown by Liquid Phase Epitaxy

“…The spectra of the layer measured from the top and side surfaces are similar and contain the same line at 321 cm -1 . With respect to the substrate, the line for the layer is broadened (FWHM ~12 cm -1 ) and reduced in intensity which agrees with the previous observations [38].…”

Irradiation effects in CaF2 probed by Raman scattering

“…Thus, the large difference in the energy transferred between the pulsed and cw lasers indicates that annealing of the colloids because of melting is probably not the process governing bleaching of our ion‐irradiated samples. The wavenumber thermal dependency of the T 2g mode in conjunction to the experimental resolution (better than 2 cm −1 ) suggests that the induced temperatures did not surpass 350 K. We assume that recombination of defects by diffusion through an energy barrier is a more plausible process. In fact, energies determined for anion and cation diffusion in CaF 2 lies around 1.92 and 3.8–5.16 eV, respectively .…”