Synergistic WO3 Incorporation and Thermal Phase-Transition Engineering for Tunable Nonlinear Optical Switching in V2O5/WO3 Heterojunction Films

In this work, V2O5/WO3 heterojunction films with tunable nonlinear optical (NLO) responses were fabricated by magnetron sputtering and subsequent thermal annealing. The influence of WO3 incorporation and annealing treatment on the structural evolution, chemical states, optical properties, and nonlinear absorption behavior of the heterojunction films was systematically investigated. By increasing the annealing temperature to 650 °C, the α to β phase transition of V2O5 was achieved, accompanied by lattice reconstruction, variation of defect-related states, and modification of electronic structures. Compared with pristine V2O5 films, the introduction of WO3 effectively modifies the phase evolution process and enables nonlinear absorption regulation at reduced annealing temperatures. The nonlinear optical response gradually evolves from reverse saturable absorption (RSA) to saturable absorption (SA), which is associated with the combined effects of phase-transition-induced electronic reconstruction, defect-state modulation, and interfacial coupling between V2O5 and WO3. The nonlinear absorption coefficient β can be continuously regulated from to cm/W through cooperative control of WO3 content and annealing temperature. Furthermore, finite-difference time-domain (FDTD) simulations reveal enhanced localized electromagnetic-field distributions at the V2O5/WO3 heterointerface, suggesting improved optical-field confinement and nonlinear light–matter interaction. These results demonstrate that WO3-assisted heterointerface engineering combined with thermal phase-transition regulation provides an effective approach for designing oxide-based nonlinear photonic materials with controllable optical switching characteristics.