In this study, the energy gap-refractive index relations of perovskites are examined in detail. In general, the properties of perovskites are dependent on the structural reorganization and covalent nature of their octahedral cages. Based on this notion, a simple relation governing the energy gap and the refractive index is proposed for perovskites. The results obtained with this relation are in good accord with the literature values and are consistent with some well-established relations.

The refractive index of solids gauges their transparency to incident light, while the energy gap determines the threshold for light absorption. This paper provides a mathematical formulation for the relationship between the refractive index and the energy gap. It is also established that this formulation aided in the unification of the Moss, Ravindra, and Herve–Vandamme relationships.

Halide perovskites are potential candidates for their use in solar cells. In this study, an investigation of the structural, mechanical and electro-optical properties of $$\mathrm{ABX}_{3}$$ABX 3 ( $$A=K, Rb, Cs$$A = K , R b , C s ; $$B=Ge, Sn, Pb$$B = G e , S n , P b and $$X=Cl,Br,I$$X = C l , B r , I ), under isosymmetric compression, is presented. All the calculations are performed with generalized gradient approximation schemes. We have examined the effect of cation and anion substitution on their overall properties.

The absorption spectrum of a material reveals the absorbed light frequencies, characteristic peaks, and the line width of absorption bands. This information is critical for understanding the energy levels involved in the absorption process as well as the material's electronic structure. In this study, an equation connecting the absorption line width with the static dielectric function is derived for narrow and wide gap materials. It is then compared with the Penn model. It has been found that the constant in the Penn model has a value that is restricted to the range of 0.5 to 1. Application of this equation to various narrow and wide gap materials is then discussed.