Qualitative analysis of relationship between refractive index and atomic parameters of solid materials

The refractive index is one of the important parameters describing the optical properties of solid materials. However, it is difficult to obtain a quantitative relation between the refractive index and the structure and composition of materials. A qualitative relation between the refractive index and some atomic parameters of materials was proposed and demonstrated by some oxide optical crystals. A parameter P = r(-) / F = r(-) / ( r(+) DeltaxD) is defined, in which Deltax is the difference of the electronegativities between cations and anions in the materials and r(+) and r(-) are the radii of cations and anions respectively. On the other hand, the factor D was introduced to describe the effect of mass difference of the ions. It is demonstrated by both theoretical discussion and experimental data that refractive index is a decreasing function of parameter P. The relation may be useful for the investigation of optical materials.