Concentration tuned bandgap and corresponding nonlinear refractive index dispersion in Ga-Ge-Se nanocolloids

Abstract

Solution-processing of chalcogenide glass materials has attracted attention for the fabrication of photonic devices. We have carried out linear and nonlinear optical studies on Ga9Ge27Se64 nanocolloidal solutions with varying concentrations and witnessed the opportunity for engineering the optical properties of the material by simply changing the concentration of solute in the solvent. An enhancement of bandgap, deterioration, and blue shift in the band tail states with decrease in concentration were observed from the absorption spectra. Open and closed aperture Z-scan studies reveal tunability of nonlinear absorption coefficient (β) and nonlinear refractive index (n2). As the bandgap approaches the one photon absorption edge, the material shows very large negative nonlinear refraction and also "two step photon absorption" due to the presence of intermediate tail states. The radial phase shift (Δφ0) induced after travelling through the nanocolloidal solution with respect to bandgap is plotted and we predict that the variation of Δφ0 is governed by a quadratic polynomial of Eg. © 2013 AIP Publishing LLC.