Nd induced changes in IR spectra of CaWO4 single crystals

CaWO4 and Nd:CaWO4 (0.8 at.% Nd) single crystals were grown from the melt by the Czochralski technique in air. The growing conditions for single crystals were calculated using the hydrodynamics equations for the buoyancy-driven and forced convection whereas the rate of crystal growth was experimentally obtained. The infrared reflectance spectra of Nd:CaWO4 and CaWO4 single crystals were recorded in the range 50-5000 cm−1 at room and LN2 temperatures. Two oxygen Eu modes showed a splitting. That especially concerns the lower one where the splitting is even pronounced with the Nd doping. Instead of the earlier attempts based on a symmetry breaking or an activation of forbidden modes, we suggest that a strong anharmonicity is the source of this effect. In addition, the crystal-field splitting in the Nd:CaWO4 mid infrared spectra was discussed.