Observation of polymorphic structure transition in phosphorus ion-implanted V2O5 thin films

Phosphorus (P) ion implantation was employed to study the fluence-dependent polymorphic evolution in α-V2O5 thin films grown by pulsed laser deposition. Grazing incidence X-ray diffraction confirms the orthorhombic α-V2O5 phase in pristine films, and implantation introduces lattice distortion and alters the preferred crystal orientation. Raman spectroscopy indicates the appearance of β-V2O5 related vibrational modes at lower fluences, suggesting a partial α→β phase transformation, followed by partial recovery toward the α-phase at the highest fluence due to defect recombination. Optical measurements reveal a noticeable band gap reduction from ∼2.4 eV (pristine) to ∼1.97 eV at lower fluences, mainly attributed to implantation-induced oxygen vacancies and defect states, whereas a slight blue shift at the highest fluence is associated with defect annihilation. Deconvoluted photoluminescence spectra further support variations in oxygen-vacancy-related emission bands. Synchrotron-based X-ray absorption spectroscopy shows a fluence-dependent variation in the t2g/eg orbital intensity ratio, indicating changes in V–O hybridization and local symmetry accompanying the α↔β structural evolution. Monte Carlo SRIM simulations further validate the atomic displacement processes responsible for defect formation and phase modification. Overall, 100 keV P-ion implantation enables controlled tuning of defect density and polymorphic phase behavior in V2O5 thin films, highlighting their potential for multifunctional gasochromic and optoelectronic applications.