Contribution to molecular mechanism of optical nonlinearity and electric conductivity of 3-nitroaniline single crystals by dielectric, electric and quantum chemical studies

The measurements of electric permittivities, of electric DC conductivity, and of the current-voltage characteristics at various temperatures and field frequencies were performed for the single crystals of 3-nitroaniline (m-NA). The 1.77 eV energy gap in the band structure, calculated by quantum chemical methods, is compared with the electronic transitions energies known from literature and with the experimentally found 0.40 eV activation energy of conductivity. The sign reversal of the current during the switch-on/off of the 980 nm diode laser beam and of the applied voltage seems to originate from the electrooptic Pockels effect and to be connected with the dynamical disorder in the crystal. The appearance of the current confirm the generation and detrapping of charge carriers (polarons) by near IR (NIR) radiation. These data indicate the electret features of the crystal. The mechanisms of electric conductivity and optical nonlinearity in the solid m-NA are proposed. (C) 2009 Elsevier B.V. All rights reserved.