Breaking the bottleneck of simultaneously wide band gap and large nonlinear optical coefficient by a "pore reconstruction" strategy in a salt-inclusion chalcogenide.

ABSTRACT

The template-based design of the crystal structure is a direct and highly efficient method to achieve optimal nonlinear optical (NLO, meaning second-order NLO) performances. The structural flexibility of porous salt-inclusion chalcogenides (SICs) provides an alternative platform for modulating the enlargement of the band gap (that is generally positive with laser-induced damage threshold) and second harmonic generation (SHG) response simultaneously. By applying the "pore reconstruction" strategy to SIC [K3Cl][Mn2Ga6S12] (1), a new derivative K3Rb3[K3Cl][Li2Mn4Ga12S27] (2) is successfully isolated, which unusually features a heterologous nanopore framework with inner diameters of 8.90 and 9.16 Å. Guided by such a strategy, compound 2 possesses the widest band gap (3.31 eV) among the magnetic NLO chalcogenides; this finding is dominantly attributed to the porous structure and the "dimensional deduction" effect. Moreover, phase 2 displays a remarkable phase-matchable SHG intensity (1.1 × AgGaS2 at the incident laser of 1910 nm) that originated from the oriented alignment of NLO-functional motifs, as well as the rich terminal S atoms in the nanopore structure. Furthermore, the "pore reconstruction" strategy offers an efficient pathway to explore potential NLO candidates with excellent comprehensive performances; in particular, it settles the conflicting issue of enhancing the band gap (>3.0 eV) and SHG intensity (>1.0 × AgGaS2) concurrently.