Optical transitions in NaCrS2

A Kramers-Kroenig analysis of the reflectivity data, over a wide photon-energy range, at room temperature, from the basal plane (Eperpendicularc) of single crystals of the layer-type compound, NaCrS2, has been performed to obtain those optical functions such as epsilon1(E), epsilon2(E), n/sub eff/(E), and J(E) which are pertinent to the study of the electronic band structure of a material. The results are presented and discussed. Strong and sharp excitonlike peaks have been observed on the epsilon2(E) spectrum and these peaks have been attributed to the presence of ligand-to-metal charge-transfer transitions in NaCrS2. The Cr3+ d orbitals are envisaged as discrete and localized (not Bloch states) within the electronic bonding of NaCrS2. The results of this Kramers-Kroenig analysis of the NaCrS2 reflectivity data support the rigid-ionic model, for this material, proposed previously by Khumalo and Hughes [Phys. Rev. B 22, 4066 (1980)]