Tailoring the properties of physical vapor deposition grown α-MoO₃ as an active optoelectronic material: Study on the effect of thickness and proton irradiation

Here, we report the synthesis of layered α-MoO₃ flakes using the physical vapor deposition (PVD) technique and mechanical exfoliation of α-MoO₃ ribbons (obtained from the PVD technique). Proton irradiation has been carried out on the exfoliated multilayer α-MoO₃ flake using a 30 keV source with a fluence of 10¹⁶ ions/cm² to tune the light emission from this material. The excitation wavelength-dependent study has been carried out on the proton irradiated α-MoO₃ flake. Interestingly, a sharp photoluminescence (PL) peak emerges in the proton irradiated α-MoO₃ flake at 540 nm, which is absent in the non-irradiated flakes, and the proton irradiation-induced PL is found to be independent of the excitation wavelength, indicating the formation of localized defect states. Furthermore, the temperature-dependent PL studies on the proton-irradiated flakes confirm the robust stability of the emission. A rigorous theoretical calculation has been carried out to understand the origin of the additional peak at 540 nm in PL spectra. Results obtained from density functional theory (DFT) calculations suggest that the PL emission originates due to the presence of oxygen defect states in the irradiated α-MoO₃ flake, while such additional peak at a lower energy range is absent in the case of non-irradiated α-MoO₃. The present study can be useful in exploring proton irradiated α-MoO₃ for optoelectronic applications.