[Sr4Cl2][Si3S9]: Ultrawide-bandgap salt-inclusion thiosilicate nonlinear optical material with unprecedented tri-polymerized [Si3S9] clusters†
Abstract
Adjusting the inherent incompatibility between a wide optical bandgap (Eg) and strong second-harmonic-generation (SHG) response (dij) has become an urgent challenge for the design and exploration of outstanding infrared nonlinear optical (IR NLO) materials. To address this, a new salt-inclusion thiosilicate, [Sr4Cl2][Si3S9], exhibiting the first discovered tri-polymerized [Si3S9] clusters, was successfully designed and synthesized by combining the native performance advantages of halides and sulfides. Detailed experimental and theoretical investigations showed that the uniformly aligned [Si3S9] functional groups could make a great contribution to the large phase-matching (PM) dij (1.2 × AgGaS2), while the ionic salt enabled a positive blue-shift of the absorption edge to achieve the widest Eg (4.22 eV) reported among all known NLO chalcohalides. Furthermore, [Sr4Cl2][Si3S9] is the first example showing a superior balance between Eg > 4.0 eV and dij > 1.0 × AgGaS2 in the PM chalcohalide system and could thus effectively eliminate the undesirable property incompatibility, indicating that salt-inclusion thiosilicates are potential research candidates for exploring ultrawide-bandgap IR SHG materials.