Metallic Ni-Ni Bonding and Defect-Mediated Electronic Reconstruction in Ion-Implanted Layered V2O5

V2O5 thin films were deposited by radio-frequency magnetron sputtering and subsequently modified by 30 keV Ni ion implantation to a fluence of 1 × 1017 cm−2. The structural, electronic, and optical properties are investigated by a combination of experimental methods and theoretical calculations. XRD and Raman confirm that the orthorhombic layered structure (α-V2O5) is preserved after implantation, with no secondary crystalline phases. XPS reveals the coexistence of Ni2+ and metallic Ni0, together with an increased V4+/V5+ ratio from 0.1 to 0.3. EPR shows a drastic drop in the V4+ signal, attributed to concentration quenching via dipole–dipole interactions. UV–Vis spectra indicate a red shift of the direct band gap (from 2.69 eV to 2.45 eV) but a slight increase in the indirect gap (from 2.31 eV to 2.36 eV), which is explained by the Burstein–Moss effect due to a high density of electron donors. Cathodoluminescence intensity decreases strongly after implantation, confirming that Ni acts as an efficient luminescence quencher. DFT calculations for a realistic V:Ni ratio of 3:1 show that Ni atoms partly form metal–metal bonds, leading to the appearance of metallic states near the Fermi level without destroying the layered V2O5 host. The combination of preserved layered architecture, enhanced V4+ concentration, and modified optical and electronic properties demonstrates the potential of Ni implantation as a route for tuning V2O5-based functional materials.