Electron-phonon contribution to electrooptical coefficient in Ca4GdO(BO3)(3) single crystals

Electrooptical r(222) coefficient in new synthesized (Ca4GdO(BO3)(3)) (GdCO B) single crystals has been measured at room and liquid nitrogen temperatur e. To separate electronic and phonon contributions we carry out experimenta l measurements and theoretical calculations. To determine electronic contri butions we have used experimental measurements for the SHG (lambda = 1.06 m u m). We also measured electrooptics tensor coefficients at lambda=0.694 mu m as well for the IR spectral region within the 1.2-2.45 mu m. From temper ature dependencies within the 77-295 K we evaluate phonon harmonic and elec tron-phonon anharmonic contributions. Using ab initio norm-conserving pseud opotential calculations and Green function evaluations of electron-phonon c ontributions we estimate quantitatively electron-phonon contributions. A go od agreement between the experimental and theoretical data is achieved. The presented approach can be proposed for another complex crystals in order t o receive an information concerning the origin of the observed phenomena. ( C) 1999 Elsevier Science B.V. All rights reserved.