Optical Properties of Molybdenum Oxide Thin Films

Molybdenum oxide thin films exhibit a rich interplay of electronic structure and light–matter interaction that underpins a wide range of optoelectronic applications. The principal phases of interest—orthorhombic α-MoO₃, monoclinic β-MoO₃ and metastable hexagonal h-MoO₃—each present distinct optical band gaps typically in the range 2.7–3.3 eV. Variations in stoichiometry, film thickness and deposition conditions govern the density of gap states and suboxide regions, which in turn modulate absorption edge sharpness, refractive index dispersion and photoluminescence efficiency. Surface defects and dopant incorporation can introduce mid-gap levels that enhance visible-light absorption or yield fast, reversible photochromic behaviour. Careful control of crystallinity and phase purity by techniques such as atomic layer deposition, sol-gel processing or sonochemical synthesis allows tuning of optical constants for antireflection coatings, photodetectors and light-emitting devices. Moreover, anisotropic optical responses arising from layered structures enable polarisation-sensitive detection. Recent advances have focused on minimising undesirable scattering losses and maximising quantum efficiency in thin-film geometries, paving the way for integration into smart windows, optical sensors and energy-harvesting architectures.

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Technical terms

Thin film: A layer of material with thickness on the order of nanometres to micrometres, deposited onto a substrate.

Band gap: The energy difference between the valence band and conduction band in a semiconductor, determining the wavelength of light absorbed or emitted.

Photoluminescence: Emission of light from a material following absorption of photons, revealing information on electronic structure and defect states.

Refractive index: A dimensionless number describing how light propagates through a medium, affecting reflection and transmission at interfaces.

References

1. Exploring the optical properties of molybdenum trioxide: approach of theory modeling and depositions techniques. Advances in Physics X (2025).
2. Atomic layer deposition of crystalline molybdenum oxide thin films and phase control by post-deposition annealing. Materials Today Chemistry (2018).
3. Structural and optical properties of sol-gel synthesized h-MoO 3 nanorods treated by gamma radiation. Nano Express (2020).
4. Calcination temperature dependent structural modifications, tailored morphology and luminescence properties of MoO3 nanostructures prepared by sonochemical method. Journal of Science Advanced Materials and Devices (2018).