New multi-functional infrared materials revealed

Scientists from China have advanced our knowledge of the interesting properties of multi-functional inorganic materials, in particular how some infrared non-linear optical (NLO) materials can demonstrate remarkable NLO characteristics as well as various other physicochemical properties. With such materials becoming an increasing focus of materials research due to their possible future applications, the team were able to show that some of the infrared NLO materials – those containing positively charged ions with d¹⁰ configuration – can offer certain useful non-linear optical behavior and thermochromism properties.

The team of researchers, who were led by Shilie Pan from the Xinjiang Technical Institute of Physics & Chemistry of the Chinese Academy of Sciences, have had their paper, entitled ‘BaCdSnS₄ and Ba₃CdSn₂S₈: Syntheses, structures, and non-linear optical and photoluminescence properties’, published in the journal Dalton Transactions [Zhen et al Dalton Trans. (2016) DOI: 10.1039/C6DT01537A]. In the study, they analyzed two metal sulfides containing the cations with d¹⁰ configuration, including Cd²⁺, before synthesizing the two metal sulfides BaCdSnS₄ and Ba₃CdSn₂S₈, which are non-centrosymmetric metal chalcogenides, using the solid-state method.

They were synthesized using a high temperature solid-state reaction in an evacuated silica tube, before the crystal structures of BaCdSnS₄ and Ba₃CdSn₂S₈ were measured with single crystal X-ray crystallography technology. BaCdSnS₄ was found to crystallize in the orthorhombic space group Fdd2, while Ba₃CdSn₂S₈, on the other hand, crystallizes in the space group I-43d. On comparing the crystal structures of both, despite the two compounds possessing the same building units in their structures – CdS₄, SnS₄ and BaS₈ – the team found them to have different structures. Ba₃CdSn₂S₈ showed a 3D framework composed of the interconnection of CdS₄ and SnS₄ groups, which differs from the 2D layer structure present in BaCdSnS₄.

When the researchers explored the properties of the NLO, they discovered that BaCdSnS₄ and Ba₃CdSn₂S₈ presented good powder second-harmonic generation (SHG) intensities at 2.09 μm laser pumping that were ∼5 and 0.8 times better than that of AgGaS₂ in the particle size 38–55 μm, respectively. This finding signifies that they could provide some potential as infrared NLO materials. In addition, measurements taken on the photoluminescence of the two compounds demonstrated that they exhibit the blue and green light emission peaks at 485 and 530 nm, and can also operate as light emitter optical devices. The study therefore offers a viable approach to preparing new multi-functional inorganic materials through this introduction of d¹⁰ elements.