Revealing the Effects of Defect States on the Nonlinear Absorption Properties of the TlInsse and Tl₂In₂S₃Se Crystals in Near-Infrared Optical Limiting Applications

Abstract

The present study represents the effect of defect states on the nonlinear absorption and optical limiting performances of TlInSSe and Tl 2 In 2 S 3 Se single crystals with near-infrared excitations. The band gap energies were 2.2 and 2.22 eV, and the Urbach energies were 0.049 and 0.034 eV for TlInSSe and Tl 2 In 2 S 3 Se, respectively. The trapping time of localized defect states was found to be 8 ns by femtosecond transient absorption measurements. The analysis of open-aperture Z-scan data depends on two different fitting models to determine the effect of defect states on the nonlinear absorption (NA) properties of the studied crystals. Model 1 only considers two-photon absorption (TPA), while model 2 includes one-photon absorption (OPA), TPA, and free carrier absorption (FCA). The NA coefficients ( ß eff ) obtained from model 2 are higher than the values ( ß ) obtained from model 1 at the same intensities, revealing that defect states contribute to NA through OPA. The optical limiting properties of the TlInSSe and Tl 2 In 2 S 3 Se crystals were examined under 1064 nm wavelength excitation. The limiting thresholds were found to be 1.16 and 0.27 mJ/cm 2 at 29.8 GW/m 2 and 99.5 GW/m 2 input intensities, respectively. The results show that TlInSSe and Tl 2 In 2 S 3 Se crystals have promising potential for near-infrared optical limiting applications.