Electronic structure and optical properties of LiNbO₃ crystal doped with Zn, Fe, and Cu: a first-principles calculation

This study employs first-principles calculations to explore Zn/Fe/Cu co-doped LiNbO₃ crystals for holographic storage optimization. Results reveal that Cu 3d and Fe 3d orbitals govern impurity states within the bandgap, while Zn²⁺ doping modulates defect configurations via concentration-dependent site occupation. Below threshold concentrations, Zn²⁺ preserves Fe³⁺/Cu²⁺ occupancy at Li sites, whereas excess Zn²⁺ drives Fe³⁺/Cu²⁺ to Nb sites due to steric effects. High [Li]/[Nb] ratios suppress intrinsic defects, enabling self-compensated Fe_Nb²⁻+Cu_Li⁺+Zn_Li⁺ complexes that intensify 452 nm (Cu-related) and 649 nm (Fe-related) absorption peaks. The optimized configuration of high [Li]/[Nb] ratios model exhibits enhanced photoconductivity and reduced holographic writing time through minimized electron trapping and improved charge transport. These synergistic effects arise from tailored defect engineering, where Zn²⁺ optimizes dopant distribution while Li-rich conditions stabilize the defect complex. The dual absorption peaks facilitate efficient charge transfer for holographic recording and readout, positioning Zn:Fe:Cu:LiNbO₃ crystal as a promising candidate for high-speed, high-fidelity optical storage systems with balanced photo response and damage resistance.