Halonitrides Zn₂NX (X=Cl,Br): Novel Mid-Infrared Nonlinear Optical Materials

Continuously, nitrides are mainly regarded as semiconductors or thermal conductivity materials and applied in photonic devices. In this work, we proposed that nitrides may also be a new system for mid-infrared (mid-IR) nonlinear optical (NLO) materials. Meanwhile, we first report the halonitrides Zn₂NX (X = Cl, Br) as mid-IR NLO crystals, which were synthesized by a solid–liquid reaction. Both compounds show excellent optical properties including large band gaps (3.21 and 3.28 eV), strong second-harmonic generation responses (0.9 and 0.8 × AGS), a wide IR transparent range (0.37–8.0 μm for Zn₂NBr) and moderate birefringences (Δn = 0.060 and 0.063). Also, the powder laser damage threshold (LDT) measurements revealed that they had high LDTs (20.7 and 25.9 × AGS). This study suggests that not only nitrides may be potential and outstanding mid-IR NLO candidates but also the combination of different anions into one structure will be a feasible strategy to discover high-performance NLO materials.