Citation: Abou-Elnour, H.A.; Osman, M.B.S.; Fadel, M.; Shakra, A.M. Investigation of the Optical Properties for Quaternary Se 60−x Ge 35 Ga 5 Sb x (x = 0, 5, and 10) Chalcogenide Glass. Materials 2022, 15, 6403. https://doi.org/10.3390/ ma15186403 Academic Editor: Marcel Poulain Received: 25 July 2022 Accepted: 8 September 2022 Published: 15 September 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). materials Article Investigation of the Optical Properties for Quaternary Se 60-x Ge 35 Ga 5 Sb x (x = 0, 5, and 10) Chalcogenide Glass Huda Allah Abou-Elnour 1,2, * , M. B. S. Osman 1 , M. Fadel 3 and A. M. Shakra 3 1 Physics Department, Faculty of Women for Arts, Science and Education, Ain Shams University, Cairo 11566, Egypt 2 Environmental Research Department, National Institute of Occupational Health and Safety (NIOSH), Cairo 2208, Egypt 3 Semiconductor Lab., Physics Department, Faculty of Education, Ain Shams University, Cairo 11341, Egypt * Correspondence: hudaallah.hse@gmail.com or hudaallah.said@women.asu.edu.eg; Tel.: +20-10-0462-1948 Abstract: A quenching technique was used to prepare the chalcogenide system of the Se 60−x Ge 35 Ga 5 Sb x (x = 0, 5, and 10 at. %), which was deposited as thin films onto glass substrates using a thermal evaporation technique. X-ray diffraction patterns were used for structure examination of the fabricated compositions, which exposes the amorphous nature of the deposited samples. Meanwhile, the chemical compositions of the prepared samples were evaluated and calculated via the energy-dispersive X-ray spectroscopy (EDX), which was in agreement with the measured compositional element percentages of the prepared samples. Based on the optical reflectance R and transmittance T spectra from the recorded spectrophotometric data ranging from 350 to 2500 nm, the influence of the Sb element on the Se 60−x Ge 35 Ga 5 Sb x thin films’ optical properties was studied. The film thickness and the refractive index were calculated via Swanepoel’s technique from optical transmittance data. It has been observed that the films’ refractive index increases with increasing x value over the spectral range. The refractive index data were used to evaluate the dielectric constants and estimate dispersion parameters E o and E d using the Wemple–DiDomenico model. The optical energy gap E opt g was calculated for the tested compositions. The result of the optical absorption analysis shows the presence of allowed direct and indirect transitions. Keywords: optical properties; chalcogenide glasses; thin films; dispersion energy 1. Introduction Amorphous chalcogenide (ChGs) thin-film compositions have attracted the interest of researchers in recent decades due to their broad and promising modern electronics applications in technological devices [1,2]. Chalcogenide materials have one or more elements, such as Se, S, and Te [1,3–7]. They are of particular interest due to their properties: high transparency in the middle and far-infrared wavelengths, limited optical absorption, high refractive index, reversible phase transformation, insignificant ambient moisture susceptibility, etc. [4,6]. The nonlinear properties of these chalcogenide materials are two or three times greater than ordinary glasses, which makes them attractive for nonlinear optics [1]. Furthermore, they have excellent transmission from visible to far-infrared; their infrared transmission range is between 1 and 16 μm, which mainly covers the two atmospheric windows of 3–5 and 8–12 μm[8]. This is in addition to their good chemical and physical features, which can be used in high-precision molding technology [9]. These properties make this type of material highly recommended for mid- and far-infrared applications [8] such as IR (infrared) lenses and IR detectors and suitable for producing different medical, military, and civil applications [10]. Chalcogenide glasses (ChG) properties can be changed by changing the doping ele- ments, processing techniques, and film deposition methods on the substrate [11]. A number Materials 2022, 15, 6403. https://doi.org/10.3390/ma15186403 https://www.mdpi.com/journal/materials