Theoretical studies of nonlinear optical properties of compounds K(4)Ln(2)(CO3)(3)F-4 (Ln=Pr, Nd, Sm, Eu, Gd)

K(4)Ln(2)(CO3)(3)F-4 (Ln=Pr, Nd, Sm, Eu, Gd) is a special type of frequency doubling compound, whose crystal structure exhibits a scarcity of fluorine ions. This leads to two different coordination polyhedrons in the general position of K(2) atoms: [K(2)O6F(1)(2)F(2)] and [K(21)O6F(1)(2)] in a 2/1 r atio. The chemical bonding structures of all constituent atoms of the compo und K4Gd2(CO3)(3)F-4 (KGCOF) are comprehensively studied; moreover, the rel ationship between the chemical bonding structure and the nonlinear optical (NLO) properties is investigated from the chemical bond viewpoint. The theo retical prediction of the NLO tensor coefficient d(11) of KGCOF is in agree ment with experimental observation. Theoretical analyses show that the nonl inearity of this crystal type mainly originates from K-O bonds. In addition , the correlation between the NLO tensor d(11) and the refractive index n(0 ) of KGCOF is discussed. (C) 2000 American Institute of Physics. [S0021-897 9(00)07506-X].