3RD-ORDER NONLINEAR-OPTICAL PROPERTIES OF SOL-GEL-DERIVED V2O5, NB2O5, AND TA2O5 THIN-FILMS

The third-order nonlinear optical properties of sol-gel-derived V2O5, Nb2O5, and Ta2O5 thin films have been investigated by the third-harmonic-generation method, and the effect of the metal-oxygen bond length on the third-order nonlinear optical susceptibility chi((3)) has been examined. The chi((3)) values of V2O5, Nb2O5, and Ta2O5 thin films were 1.1 x 10(-11), 1.3 x 10(-12), and 6.1 x 10(-13) esu, respectively, which corresponds to an increase in the average bond length l(b) of the order of V-O (l(b) = 0.183 nm), Nb-O (l(b) = 0.200 nm), and Ta-O (l(b) = 0.204 nm). The current and previous results indicate that chi((3)), of these transition metal oxides with the empty d orbitals is dominated mainly by the metal-oxygen bond length rather than the valence of the metal cation. It is predicted on the basis of Lines' model that transition metal oxides with the shortest l(b) exhibit the highest chi((3)), whereas nontransition metal oxides with the longest l(b) exhibit the highest chi((3)).