Thermo-optic dispersion formulas for monoclinic double tungstates KRe(WO4)2 where Re = Gd, Y, Lu, Yb

Thermooptic coefficients dn/dT for monoclinic potassium (rare-earth) double tungstates KRe(WO4)(2) (where Re = Gd, Y, Lu, Yb) were determined at eight wavelengths in the range of 0.3-1.1 mu m by a laser beam deviation method. In the long-wavelength range all the dn/dT values were found to be negative and near constant, while dn/dT(lambda) dependence is especially pronounced in the short-wavelength range where thermooptic coefficients change sign to positive. Linear thermal expansion coefficients were measured in KRe(WO4)(2) along the optical indicatrix axes by a dilatometric technique. Volumetric thermal expansion effect was found to dominate over the bandgap change influence on temperature dependence of the refractive index. Thermooptic dispersion formulas were derived for KRe(WO4)(2) as series in 1/lambda(2). The influence of Yb and Nd doping on the dn/dT values was investigated, resulting in prediction of thermooptic coefficients evolution in the isostructural KYxYb(1-x)(WO4)(2) and KYbxLu((1-x))(WO4)(2) series. (C) 2011 Elsevier B.V. All rights reserved.