Shift of band gap from indirect to direct and optical response of CaO by doping S, Se, Te

•Lattice constants vary inversely to the bulk moduli in these alloys.•Structural parameters vary non-linearly by doping concentration.•Binaries have indirect band gap while their ternary alloys show direct band gap.•The band gaps also varies non-linearly with the concentration.•The alloys can be utilized in solar cells and other optoelectronic devices.

Density functional theory is applied to explore the structural, electronic and optical properties of chalcogen (S, Se, Te) doped CaO in rocksalt phase. The calculated structural parameters are found in good agreement to the available experimental data. Lattice constants vary inversely to the bulk moduli in these alloys. Moreover, these parameters vary non-linearly as a function of doping concentration. The parent binary compounds have indirect band gap while their ternary alloys have direct band gap nature. Zero frequency dielectric constant, reflectivity and refractive index increase by increasing Y (Y = S, Se, Te) concentrations in CaO. The threshold points and the position of peaks in the optical spectra shift towards lower energies by increasing concentrations. The obtained results for the alloys such as the direct band gap and high absorption in visible and ultraviolet regions indicate the significant optical activity of these alloys in solar cells and various optoelectronic devices.

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