Vibrational investigations of lanthanide doped strontiumbarium niobate (SBN) crystals

Strontium barium niobate (Sr(0.5)Ba(0.5)Nb(2)O(6) and Sr(0.6)Ba(0.4)Nb(2)O(6)) single crystals doped with 1-2.5 mol% of the luminescent ions Eu(3+) and Er(3+) have been investigated using Raman and IR spectroscopy. The vibrational spectra of SBN crystals are dominated by broad and multi-component bands related to the internal vibrations of the NbO(6)(7-) octahedra. In order to interpret the experimental vibrational spectra of SBN crystals the quantum-chemical calculations (DFT) for the NbO(6)(7-) anion have been carried out. As a first approximation, the dynamics of isolated NbO(6)(7-) anions have been taken into account. The calculated vibrational frequencies for the free NbO(6)(7-) ion are in fair agreement with the frequencies of modes observed in experiment. The discrepancies are attributed to the distortion of the niobate octahedra in the actual crystal structure and to the presence of disorder and doping with impurity ions in SBN crystals.