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In this paper, the influence of thickness and post deposition annealing temperature on thermally evaporated molybdenum oxide films has been studied. The X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) are used for crystal structural and surface morphological characterization of the films, respectively. The XRD analysis showed that the presence of α-MoO3 and MoO2 crystalline phase of the films annealed at elevated temperature ~ 250 °C after deposition. The optical constants are determined from UV–Vis transmission spectra. The optical band gap and Urbach energy is found to be temperature dependent. The refractive index of the films is estimated by the optical method as well as cross-sectional SEM image analysis. It is found that the refractive index of the films increases from ~ 1.70 to 2.03 with the decrease in film thickness from ~ 2.9 to 1.7 µm. It is also observed that the refractive index decreased from ~ 2.03 to 1.61 with the increase in post deposition annealing temperature from room temperature (RT) to ~ 250 °C. Moreover, extinction coefficient, optical conductivity, porosity, and film density are investigated as a function of source-substrate distance and post deposition annealing temperature. The Photoluminescence (PL) properties of the films are also investigated by recording spectra under the excitation wavelength at 250 nm.

In this paper, the dispersion parameters of Molybdenum Oxide thin films viz: oscillator energy, dispersion energy, transition moments, static refractive index, oscillator strength, and oscillator wavelength are estimated via Wemple–DiDomenico (WDD) single oscillator model. The crystal structural, surface morphological, and optical transmission properties of Molybdenum Oxide thin films are also investigated so as to extract vital in-put parameters for WDD model. The X-ray Diffraction and Fourier Transform of Infrared analysis confirm that the film fabricated at substrate temperature ~ 300 °C under goes a successful dual phase transformation from amorphous to α- and β-MoO3 crystalline phase. Static refractive indices of the films are found to be vary from ~ 1.84 to 2.04 with the increase of substrate temperature during the thin film growth process via thermal evaporation technique. Moreover, the optical constants viz: film density, porosity, absorption coefficient, optical band gap, Urbach energy, steepness parameter, and strength of electron–phonon interaction are also studied as a function of substrate temperature. This is to establish a correlation between optical constants and dispersion parameters in the present paper.