Anion-engineered CsInTiS₄₋ₓOₓ (x = 0.8) quantum dots for enhanced nonlinear photonics and optoelectronics

Computational modelling of anion-substituted quantum dots reveals that controlled oxygen incorporation into CsInTiS₄ nanostructures induces profound modifications in electronic structure and optical response. Therefore, in our study, we examined 20% anion-site oxygen incorporation into CsInTiS₄ (i.e., CsInTiS_3.2O_0.8 QDs) using methods based on density functional theory and dielectric function optical modelling. Our results regarding structural relaxation and simulated X-ray diffraction indicate that sulfur's substitution with oxygen induces lattice contraction and structural reorganization. This is accompanied by a change in the lattice symmetry from polar [Formula: see text] to centrosymmetric P_2/m in the optimized geometry. CsInTiS₃.₂O₀.₈ exhibits a pronounced bandgap contraction from [Formula: see text] [Formula: see text] in CsInTiS₄ to [Formula: see text], whilst the optical carrier concentration-to-effective mass ratio increases by [Formula: see text] to [Formula: see text]. Furthermore, it reveals a Wemple-DiDomenico dispersion energy of [Formula: see text], an oscillator strength of [Formula: see text], a static refractive index of [Formula: see text], and a high-frequency dielectric constant of [Formula: see text]. Moreover, carrier dynamics characterised by an ultrafast relaxation time of [Formula: see text] point to dominant scattering pathways intrinsic to the mixed-anion framework. These findings suggest that oxygen anion substitution plays a viable role in band structure engineering and light-matter interactions in a CsInTiS₄ parent lattice. Thus, the predicted narrow band gap, enhanced light-matter interaction, and oscillator strength make CsInTiS₃.₂O₀.₈ a strong candidate for infrared photodetection, tunable plasmonics, and third-order nonlinear photonics.