Sprayed nanocrystalline ZMS thin films for nonlinear optical device applications

Growth and characterization of novel Zn_(1-x)Mg_xS (ZMS) thin films for the nonlinear optical applications are reported here. ZMS thin films were deposited by industrial friendly spray pyrolysis method at optimized deposition conditions. XRD showed good crystallinity having crystallite size in the range 4.6–11 nm. It also confirmed the presence of mixed phases of zinc blende and wurtzite having strong orientation along (111) and (104) planes respectively. All the films have shown transmittance in the range 75%–90%. Detailed analysis of the transmittance data revealed a slight increase in the band gap from 3.42 eV to a maximum of 3.48 eV for 4 at% Mg doped thin films. Photoluminescence study confirmed the presence of intermediate bands in the doped thin films. Substantial change in third order optical susceptibility (χ⁽³⁾) and nonlinear refractive index (n₂) values were observed for the doped films as compared to pristine samples. Remarkably, there was a flip from saturable absorption (SA) into the reverse saturation absorption (RSA) for the doped films. Z-scan studies showed that the spray deposited ZMS thin films are suitable for the nonlinear devices such as optical limiters and modulators.