Cs3In(In4Se7)(P2Se6): A Multi-Chromophore Chalcogenide with Excellent Nonlinear Optical Property Designed by Group Grafting

Abstract

Non-centrosymmetric (NCS) and polar materials capable of exhibiting many important functional properties are indispensable for electro-optical technologies, yet their rational structural design remains a significant challenge. Here, we report a "group grafting" strategy for designing the first multi-chromophore selenophosphate, Cs₃In(In₄Se₇)(P₂Se₆), that crystallizes in a NCS and polar space group of Cm. The structure features a unique basic building unit (BBU) [In(In₄Se₁₀)(P₂Se₆)], formed through "grafting [In₄Se₁₀] supertetrahedra on the root of [In(P₂Se₆)₂] groups". Theoretical calculations confirm that this [In(In₄Se₁₀)(P₂Se₆)] BBU can achieve a "1+1>2" combination of properties from two chromophores, [In₄Se₁₀] supertetrahedron and ethane-like [P₂Se₆] dimer. That makes Cs₃In(In₄Se₇)(P₂Se₆) exhibit excellent linear and nonlinear optical (NLO) properties, including a strong second harmonic generation (SHG) response (~6×AgGaS₂), a large band gap (2.45 eV), broad infrared (IR) transmission (up to 19.5 μm), a significant birefringence (0.26 @1064 nm) as well as the congruently-melting property at ~700 °C. Therefore, Cs₃In(In₄Se₇)(P₂Se₆) will be a promising NLO crystal, especially in the IR region, and this research also demonstrates that "group grafting" will be an effective strategy for constructing novel polar BBUs with multi-chromophore to design NCS structures and high-performance IR NLO materials.

Keywords: Chalcogenides; Multiple chromophore; Nonlinear Optics; Second-Harmonic Generation; Structural Design.