Interfacial engineering-enabled nonlinear optical enhancement through OH vibrational coupling in MXene heterostructures

This study investigates the nonlinear optical (NLO) properties of the Mo₂Ti₂C₃/2-amino-3-hydroxyphenazine (Mo₂Ti₂C₃/HAP) heterostructure, which was synthesized via an ultrasonication-centrifugation method. In the Mo₂Ti₂C₃/HAP heterostructure, the HAP binds to the surface hydroxyl groups of Mo₂Ti₂C₃, enhancing interfacial electron transfer efficiency. Inelastic neutron scattering (INS) analysis and density functional theory (DFT) calculations reveal a new vibrational mode at 850 cm⁻¹ at the heterostructure interface, which is attributed to OH-coupled breathing vibrations, mediating the interaction between Mo₂Ti₂C₃ and HAP. Femtosecond transient-absorption spectroscopy analysis further indicates that this mode dominates electron-transfer dynamics from Mo₂Ti₂C₃ to HAP, leading to excited-state reabsorption within the Mo₂Ti₂C₃ lattice. This mechanism is directly evidenced by Z-scan measurements, revealing a distinct transition from saturable absorption (SA) to reverse saturable absorption (RSA), with a nonlinear absorption coefficient of βeff = 1.59 × 10⁻¹⁰ m W^-1 at 520 nm excitation. These findings highlight the potential of the Mo₂Ti₂C₃/HAP heterostructure for advanced photonic applications.