Manifestation of the size effect in the optical and spectral properties of the (N(C2H5)4)2CoCl2Br2 nanoclusters incorporated into the polymer matrix

Abstract

The spectral and non-linear properties of (N(C2H5)4)2CoCl2Br2 nanocrystallites incorporated into the polymer matrices were investigated. The temperature dependence of the photoinduced second harmonic generation (PISHG) demonstrates a remarkable dependence on temperature near the phase transitions. It has been found that the temperature of phase transition T2 in the nanostrustured ferroics could depend on host polymer matrix and is higher than those in the bulk material. It is suggested that this effect is connected with the surface tension coupled with polarization via electrostriction effect and the influence of the depolarization field arising around the surface of the nanocluster. The arising lateral pressure induces lowering of the symmetry of the metal-halogen complexes within the surface layer of the cluster. Their distortion is followed by more pronounced splitting of the degenerate energy levels due to the lower symmetry of the crystal field. The shift of the corresponding absorption bands as well as the suppression of the integral absorption in the region of the internal transition of Co2+ ion with diminishing of the nanocluster size is followed by considerable decreasing of PISHG intensity.