Dilute Soft-Cation Anchoring Stabilizes γ-NaAsSe2 against Moisture While Preserving Giant Mid-Infrared Nonlinearity

Area of Science:

• Materials Science
• Photonics
• Solid-State Chemistry

Background:

• Designing nonlinear optical (NLO) materials with high second-harmonic generation (SHG) efficiency and stability is crucial for infrared photonic applications.
• Chalcogenide crystals like γ-NaAsSe2 (γ-NAS) show promise due to high SHG susceptibility but suffer from poor ambient stability caused by moisture-assisted degradation.

Purpose of the Study:

• To address the stability limitations of γ-NAS for practical NLO applications.
• To develop a chemical strategy for stabilizing moisture-sensitive polar chalcogenides while preserving their NLO properties.

Main Methods:

• Incorporated antimony (Sb) substitution at the arsenic (As) site to stabilize the polar framework.
• Introduced dilute silver (Ag) substitution at the sodium (Na) site to form stronger Ag-Se contacts.
• Utilized Bridgman crystal growth to produce large single crystals of γ-Na0.99Ag0.01As0.95Sb0.05Se2.

Main Results:

• Synthesized stable single crystals of γ-Na0.99Ag0.01As0.95Sb0.05Se2 that remained durable under ambient conditions for 365 days.
• Preserved a giant SHG response of approximately 600 ± 15 pm/V, comparable to the pristine material.
• Demonstrated that dilute Ag substitution enhances ambient durability by forming covalent Ag-Se anchors, suppressing lattice degradation without compromising the electronic structure.

Conclusions:

• Dilute soft-cation anchoring is an effective strategy for stabilizing moisture-sensitive polar chalcogenides.
• Sb and dilute Ag co-substitution successfully enhances the stability of γ-NAS crystals, enabling their use in infrared photonic applications.
• The stabilized material retains excellent NLO performance and exhibits Type I phase-matchability.