Enhanced third-order nonlinear optical response in Sc- and V-co-doped titanium dioxide

This work reports a substantial enhancement in the third-order nonlinear optical response of (Sc,V)-co-doped TiO 2 thin films synthesized by using pulsed laser deposition. Comprehensive structural and chemical characterization confirms the substitutional incorporation of Sc 3+ and V 5+ into the rutile TiO 2 lattice, accompanied by the controlled generation of Ti 3+ states and oxygen vacancies. Linear optical spectroscopy reveals a bandgap widening from 3.07 to 4.08 eV with increasing co-dopant concentration, which is ascribed to the synergistic effects of the Sc 3+ -induced upward shift of the conduction band minimum and Burstein–Moss filling. Using the Z-scan technique with 30 ps pulses at 1064 nm, we demonstrate that co-doping simultaneously enhances the nonlinear refractive index n 2 (from 3.81 to 11.43×10 −14 m 2 /W) while suppressing the two-photon absorption coefficient β (from 5.0 to 1.58×10 −8 m/W). The resulting third-order susceptibility χ (3) reaches 1.88×10 −7 esu, representing a significant enhancement relative to undoped TiO 2 . Critically, the figure of merit values ( W ∼3.78, T ∼0.14) satisfy the stringent performance criteria required for low-loss, high-contrast on-chip photonic switches. These findings establish (Sc,V)-co-doped TiO 2 as a defect-engineered oxide platform uniquely suited for integrated nonlinear optical applications.