Unveiling the Linear and Nonlinear Optical Potential of Ag2SrTiSe4 : A First − Principles Pathway toward Next − Generation Photonic and Optoelectronic Devices

Multifunctional semiconductor materials with tunable electronic structures and enhanced optical responses are required for next-generation photonic and optoelectronic technologies. In this work, we use DFT to study the structural, electronic, bonding, linear optical, and nonlinear optical properties of the quaternary chalcogenide Ag₂SrTiSe₄ and evaluate its potential for advanced photonic applications. The tetragonal structure proposed belongs to the non-centrosymmetric space group I-42m and has an equilibrium unit cell volume of 410 ų and a bulk modulus of 51 GPa. Indirect bandgaps (using PBE and HSEo6 functionals) are 1.80 and 2.50 eV, respectively. The absorption threshold is 2.188 eV, the static refractive index is 2.28, and the dielectric constant is 5.2, as reported. Strong ultraviolet absorption (6–7 × 105 cm⁻¹) suggests UV-sensitive optoelectronic devices; the calculated static reflectivity of 15.23% further informs optical-interface engineering. In addition, the non-centrosymmetric crystal symmetry allows second-order nonlinear optical interactions; thus, we study second-harmonic generation and frequency-conversion applications. Electronic, optical, and symmetry based analyses identify Ag₂SrTiSe₄ as a candidate for further computational and experimental evaluation in integrated photonics, optical coatings, ultraviolet photodetection, and nonlinear optical technologies.

This study is significant because it provides a comprehensive first-principles assessment of the quaternary chalcogenide Ag₂SrTiSe₄ as a non-centrosymmetric semiconductor with properties relevant to photonic and optoelectronic applications. Its novelty lies in establishing the structural stability, electronic structure, bonding characteristics, and linear and nonlinear optical responses of this material within a single theoretical framework, including the prediction of indirect bandgaps from both PBE and HSE06 calculations and the identification of strong ultraviolet absorption and appreciable reflectivity. Scientifically, the work clarifies how the I-42m crystal symmetry supports second-order nonlinear optical activity and frequency-conversion capability, while the calculated refractive index, dielectric constant, absorption edge, and reflectance provide essential parameters for evaluating light–matter interaction in the material. The key contribution is the identification of Ag₂SrTiSe₄ as a promising candidate for further computational and experimental investigation in integrated photonics, ultraviolet photodetection, optical coatings, and nonlinear optical technologies.

This study uses density functional theory to investigate the structural, electronic, bonding, linear optical, and nonlinear optical properties of the quaternary chalcogenide Ag₂SrTiSe₄. The material is predicted to crystallize in a non-centrosymmetric tetragonal I-42m structure with an equilibrium volume of 410 ų and a bulk modulus of 51 GPa. Electronic structure calculations give indirect band gaps of 1.80 eV (PBE) and 2.50 eV (HSE06), indicating semiconducting behavior suitable for optoelectronic use. Optical analysis shows an absorption threshold of 2.188 eV, a static refractive index of 2.28, and a dielectric constant of 5.2, along with strong ultraviolet absorption of 6–7 × 105 cm⁻¹ and a static reflectivity of 15.23%. Because of its non-centrosymmetric symmetry, Ag₂SrTiSe₄ is also expected to support second-order nonlinear optical processes such as second-harmonic generation. Overall, the results suggest that Ag2SrTiSe4 is a promising candidate for UV photodetectors, integrated photonics, optical coatings, and nonlinear optical devices.