Optical constants, optical dispersion and group index parameters of Mn2O3 thin films

Abstract

In this work, we report on the diverse optical parameters of Mn2O3 thin films prepared by nebulized spray pyrolysis technique by the effect of spray solution concentration. X-ray diffraction study confirmed the Mn2O3 films belong to cubic structure. The Raman vibrational band observed at 636 cm−1 is related with the symmetric stretching of Mn–O bond of trivalent manganese ions (Mn3+). The surface morphological study showed that the nano-sized particles are homogenously distributed on the film surface. The films exhibit the highest transmittance in the near infrared region. The spray solution concentration induced reduction of Urbach energy (from 677 to 655 meV) indicates the decrease in degree of crystal defects in the film. The extinction coefficient of the film was obtained in the order of 10−2. It was observed that the optical dispersion threshold point (TODT) of Mn2O3 thin film is coincides with the refractive index threshold wavelength (λrtw) of the material. This was further corroborated from the intersection of phase velocity and group velocity curves at the point of λrtw or TODT. This indicates that no optical dispersion was taken place at that point and therefore the phase velocity is equal to the group velocity. The possible correlations among the data were made with the light of underlying concepts.