Short-UV Metal Halide Nitrates: Moderate SHG in K3Sb(NO3)3F3 and Enhanced Optical Anisotropy in K3Zn(NO3)X4 (X = Cl, Br)

Abstract The development of nonlinear optical (NLO) and birefringent crystals remains crucial for advancing laser science and optical technologies. The [NO3]− anionic group, characterized by a planar π-conjugated geometry, pronounced polarizability anisotropy, and a substantial hyperpolarizability tensor, is an attractive functional unit for designing NLO and birefringent materials. Guided by this structural motif, four ultraviolet (UV) metal halide nitrate crystals were synthesized: K3Sb(NO3)3F3, KSb(NO3)F3, K3Zn(NO3)Cl4, and K3Zn(NO3)Br4. K3Sb(NO3)3F3 shows a favorable second-harmonic generation (SHG) response (∼1.2 × KH2PO4, KDP) and an appropriate experimental birefringence (Δnexp = 0.086 at 546 nm) for phase-matching behavior. KSb(NO3)F3 and K3Zn(NO3)X4 (X = Cl, Br) display modest calculated birefringence (Δncal) values within the range of 0.052–0.079 at 546 nm, among which K3Zn(NO3)Br4 shows the largest Δnexp (0.096 at 546 nm). Notably, all four nitrate compounds exhibit short UV cutoff wavelengths (208–212 nm) and can be cultivated as centimeter-sized crystals, achieving dimensions of up to 1.0 × 0.7 × 0.4 cm3. Collectively, the combination of short UV cutoffs, moderate SHG responses, and large birefringence establishes nitrate-based compounds as promising candidates for UV optical applications.