Circular dichroism of some Nd-doped crystals of the langasite family

The absorption and circular-dichroism spectra of neodymium-doped crystals of langasite La3Ga5SiO14 and the compounds La3Ga5.5Nb0.5O14 and Pb3Ga2Ge3.92Si0.08O14, isostructural with langasite, are investigated in the wavelength range 320-940 nm. Electronic transitions in Nd atoms, which substitute the main cation of the salts (La or Pb) in the positions with the local symmetry C-2, are observed in the spectra. All transitions observed in the absorption spectrum are also active in the circular-dichroism spectrum. Detailed analysis is performed for several (well separated) bands: Dipole strengths D-ok, rotation strengths R-ok, and the anisotropy factors G(ok) are calculated. Some specific features of the spectra obtained are noted and their possible relationship with the structure of impurity centers of neodymium and effect on the intensity of the Stark components are discussed. (C) 2005 Pleiades Publishing, Inc.