Investigating electronic, linear and nonlinear optical characteristics of Cr-Substituted ZnS materials

Abstract

The electronic, linear, and nonlinear optical (NLO) characteristics of the Cr-substituted ZnS (ZnCrS) materials are reported within density functional theory (DFT) by using the mBJ potential. The results showed a cubic symmetry with a lattice constant decreasing as the Cr concentration increased, but the bulk modulus showed the opposite tendency. ZnS is a direct wide bandgap semiconductor; however, incorporating 75 % Cr in the ZnCrS materials causes a change in electronic bandgap nature. This change occurs due to Cr-induced defects and structural modifications, leading to new electronic transitions yielding novel optical features. The electronic and optical bandgap energy decreases with Cr content, depicting CrS as a semi-metallic material with significant light absorbance in the near-infrared and visible wavelengths accompanying the enhancement of the NLO response. It is noticed that a decrease in Εopt significantly impacted the NLO response, resulting in a significant change in the value of third-order susceptibility (χ(3)) from 5.862 × 10−11 to 2.074 × 10−9 esu. The NLO refractive index (n2) also follows the same changing trend, varying from 5.113 × 10−11 to 1.735 × 10−8 esu. This Cr-induced nonlinearity depicts strong polarizability and these materials can be significantly employed in near-infrared activated nanophotonic, photovoltaic, and optoelectronic devices.