Güler, İpekIşık, MehmetGasanly, Nizami Mamed2023-12-052023-12-052023-06http://hdl.handle.net/20.500.14411/18231432-0630https://doi.org/10.1007/s00339-023-06729-4Published by Applied Physics A Materials Science and Processing, https://doi.org/10.1007/s00339-023-06729-4, I. Guler, Physics, Inter-Curricular Courses Department, Çankaya University, 06530 Ankara, Turkey, M. Isik, Department of Electrical and Electronics Engineering, Atilim University, 06836 Ankara, Turkey, N.M. Gasanly, Department of Physics, Middle East Technical University, 06800, Ankara, Turkey, Virtual International Scientific Research Centre, Baku State University, 1148 Baku, Azerbaijan.The optical properties of TlIn(S0.25Se0.75)2 crystals were studied by ellipsometry measurements. X-ray diffraction pattern presented well-defined peaks associated with monoclinic structure. Energy dependent graphs of various linear optical parameters of the crystal were presented in the 1.25 − 4.50 eV range. The band gap and Urbach energies of the compound were found as 1.96 and 0.68 eV, respectively, from the analyses of the absorption coefficient. Refractive index spectrum was analyzed considering the single-effective-oscillator model to get oscillator and dispersion energies, zero and high frequency dielectric constants, plasma frequency. Moreover, the nonlinear refractive index, first-order and third-order nonlinear susceptibilities of TlIn(S0.25Se0.75)2 crystal were revealed in the present paper.enTlInS2, TlInSe2, ellipsometry, optical constants, bandgap energy, 2D materialsArticle