Dopant-driven photonic nonlinear optical responses in Mg₄O₃ electrides

Electrides hold tremendous potential for nonlinear optical (NLO) materials in photonics and laser technologies, yet precise control of their optoelectronic properties remains challenging. Here, we systematically design and characterize pristine Mg₄O₃ and alkali metal halide - doped electrides MX@Mg₄O₃ (M = Li, Na, K; X = F, Cl) using density functional theory (DFT) and time-dependent DFT. Dopant integration induces electronic restructuring, HOMO-LUMO gap reduction, and enhanced charge-transfer characteristics with concomitant frontier orbital redistribution. Interaction energies (-35.6 to -75.0 kcal mol^-1) indicate robust binding and thermodynamic viability, favoring p2 (located on the side of Mg₄O₃) over p1 (located on the top cavity of the Mg₄O₃) geometries; fluoride complexes exhibit the strongest interactions at dopant-host distances of 1.8-2.5 Å. The static first hyperpolarizability of pristine Mg₄O₃ (β ₀ = 9.23 × 10³ a.u.) surges more than 3-fold upon doping, peaking at 2.87 × 10⁴ a.u. for KCl@Mg₄O₃-p1. Dynamic NLO responses, including the electro-optic Pockels effect and second-harmonic generation, are markedly enhanced upon alkali-halide doping, with NaF@Mg₄O₃-p1 showing the highest EOPE response of 50063 a.u. at 1064 nm and NaCl@Mg₄O₃-p1 exhibiting the strongest SHG response of 1,201,472 a.u. at 1340 nm. UV-vis spectra confirm red-shifted absorptions (λ _max = 418-743 nm) tied to π-delocalization and intramolecular charge transfer, aligning with β _HRS and refractive index profiles. Collectively, these results demonstrate dopant chemistry and positional engineering as transformative strategies for NLO tuning, positioning Mg₄O₃ electrides as front runners for next-generation optoelectronic applications.