A Band-Orientation Co-Anchoring Strategy for the Design of a High-Performance Mid-Infrared Nonlinear Optical Crystal

Mid-infrared (MIR) nonlinear optical (NLO) crystals have long been pursued, yet the realization of a balance among key performance metrics remains a formidable challenge. Herein, we propose a band-orientation co-anchoring strategy to precisely regulate the band structures and module spatial arrangement for the rational design of high-performance MIR NLO crystals. Leveraging the deep-ultraviolet NLO KBe₂BO₃F₂ (KBBF) as a template, a novel MIR NLO Rb₃ZnV₄O₁₂Br (RZVB) crystal was successfully obtained through multimodule substitution. Importantly, the tailored tetrahedral hybridization mode effectively anchors the conduction band minimum-dominated by d⁰ cations-at a higher energy level and suppresses d-d transitions. Concurrently, structural confinement within the KBBF-derived lattice enforces the optimal alignment of distorted tetrahedra. Furthermore, RZVB displays an unprecedented second harmonic generation (SHG) enhancement mechanism, arising from a unique cross-module electron transfer. Consequently, RZVB exhibits superior linear and NLO performances, including a wide bandgap (3.25 eV), high laser threshold damage (1.07 GW/cm²@1064 nm), broad transmission window (0.382-7.6 µm), moderate birefringence (0.06@589.3 nm) and the strongest SHG response (7.7 × KDP@1064 nm and 1.45 × AGS@2.09 µm) among vanadates with bandgap exceeding 3 eV. This work presents a high-performance MIR NLO crystal and establishes a bottom-up, broadly applicable design paradigm for the tailored development of next-generation crystalline materials.