Facile syntheses of silver thioantimonates exhibiting second-harmonic generation responses and large birefringence

Abstract

Two chalcogenide crystalline compounds, [enH₂][Ag₄Sb₂S₆] (en = ethylenediamine) and [enH][Ag₂SbS₃], have been successfully synthesized by mild ionothermal and solvothermal means. [enH][Ag₂SbS₃] crystallizes in the noncentrosymmetric (NCS) and polar space group Pc, and its linear and nonlinear optical (NLO) properties have been investigated for the first time. Second harmonic generation (SHG) measurements revealed that [enH][Ag₂SbS₃] affords powder SHG performance values of 2.5 × KDP @1064 nm and 0.2 × AgGaS₂ @2100 nm. Additional particle size vs. SHG efficiency measurements indicate that [enH][Ag₂SbS₃] is phase-matchable. The calculated birefringence Δn is 0.177 at 1064 nm, which is sufficiently large (the largest value among NCS thioantimonates) to achieve phase matching. [enH₂][Ag₄Sb₂S₆] crystallizes in the centrosymmetric space group P2₁/c and its structure features a double-layered variant honeycomb-like anionic network parallel to the ac plane separated by [enH₂]²⁺ cations. The optical band gaps of [enH₂][Ag₄Sb₂S₆] and [enH][Ag₂SbS₃] are found to be 2.37 and 2.53 eV, respectively. Theoretical studies using density functional theory have been implemented to further elucidate the relationship between the band structure and NLO properties in [enH][Ag₂SbS₃].