Effect of Nd doping on the refractive index and thermo-optic coefficient of GdVO4 single crystals

Undoped and Nd (0.2, 0.6, 0.8, 1.0, 1.2 and 1.6 at%)-doped GdVO4 single crystals have been grown by optical floating zone technique. XRD analysis reveals small lattice expansion especially along c axis on Nd doping. It has been observed that the extra-ordinary refractive index (RI) of undoped GdVO4 crystals is higher than the doped GdVO4 single crystals up to 1.0 at% Nd doping, beyond which it surpasses the value of the undoped crystal. This is due to the competing effect of lattice elongation and decrease in electron density on Nd doping. The increase in RI with Nd doping is attributed to macroscopic polarization effects. Moreover, the extra-ordinary refractive index (n(e)) only increases on increasing Nd concentration, whereas ordinary refractive index (n(o)) remains unaffected within the measurement limits. The temperature-dependent RI measurements depicted a positive thermo-optic coefficient (TOC) for RI and birefringence, which is similar to 10(-5)/degrees C and is independent of doping concentration. TOC for n(e) is higher than n(o,) which has been explained on the basis of anisotropic thermal expansion. An important set of relations between TOC and wavelength (532-1551nm) has been established which is useful for estimating TOC in the temperature range of 30-150 degrees C.