H. H. Li. Refractive index of alkali halides and its wavelength and temperature derivatives. J. Phys. Chem. Ref. Data5, 329-528 (1976) and references therein. * Sellmeier formula derivation is based on a single data point and knowledge of the dielectric constants and the characteristic absorption peaks.
Sodium iodide (NaI) is a white, crystalline solid that can be prepared as transparent crystals suitable for optical applications. Notably, when doped with thallium (NaI:Tl), it becomes a scintillator material, capable of converting incident gamma rays into visible light. This property makes NaI:Tl crystals particularly valuable in radiation detection, gamma spectroscopy, and other nuclear medicine applications. However, NaI, being an alkali halide, is hygroscopic, meaning it readily absorbs moisture from the environment. Therefore, it requires careful handling and storage to prevent degradation, especially if it is to be used in optical systems.