Exploration Of New Chalcogenides With The Tetrahedral Units

Nonlinear optical?NLO?materials,as key devices for solidstate lasers,have attracted increasing attention in the laser frequency-conversion field and have become an urgent requirement for scientific and technological applications,such as fiber-optic communication,molecular spectroscopy,laser radars,laser weapons,medical diagnostics,and optoelectronic devices.However,for the IR region,only a few IR NLO materials,such as AgGaQ₂?Q=S,Se?and ZnGeP₂?ZGP?,have achieved commercial application.Unfortunately,they possess some inherent drawbacks,such as low laser damage threshold?LDT?or two-photon absorption?TPA?,which severely impede their further application.Thus in this article we have mainly explored the tetrahedra contained chalcogenides.The main work details are as follows:1.Four new quaternary chalcogenides A₂Ba₇Sn₄Q₁₆?A=Li,Na;Q=S,Se?were successfully synthesized in vacuum-sealed silica tubes for the first time.All of them crystallize in the noncentrosymmetric?NCS?cubic I 3d space group with the cell parameters ranging from 14.807 to 15.4163?and Z=4,respectively.Interestingly,their isostructures are different from the structural transformations?from tetragonal to trigonal?appearing in previously reported Na₂BaSnQ₄ compounds.As observed in their structures,?Na/Ba?Q₄ and SnQ₄ units alternately connect with each other by sharing corners to build a three-dimensional?3D?framework structure with charge-balanced Ba cations located within tunnels,which is different from the observation that the Na atoms located inside the tunnels formed by the interconnection of the BaS₈ and SnS₄ units in Na₂BaSnS₄.Optical properties?diffuse-reflection,IR,and Raman spectra?were also systematically studied and the results indicate that their optical bandgaps are in the range from 1.75 to 2.5 eV.Moreover,the second harmonic generation?SHG?responses of the title compounds were also measured to be about 0.1–0.5 times higher than that of benchmark AgGaS₂under 2.09 mm radiation.2.Two new metal chalcogenides,Ba₅Pb₂Sn₃S₁₃?BPSS?and Ba₆PbSn₃Se₁₃?BPSSe?,were successfully synthesized in vacuum–sealed silica tubes for the first time.Both of them are isostructural and crystallize in the Pnma space group of orthorhombic system.Their three-dimensional?3D?framework structures are composed of 2D layers formed by the interconnection of[?Pb/Ba?Q_n]?n=6 and 7?polyhedra and isolated SnQ₄ tetrahedra and charge–balanced Ba atoms filled into the interlayers.Note that the Q8 atoms are only surrounded by two Pb/Ba and four Ba atoms to form the distorted octahedra without the covalent Sn-Q bonds in their structures.Measured results of diffuse reflection and Raman spectra show that title compounds possess the wide transmission ranges from 0.5 to 20?m.Electronic structures and linear optical properties were also systematically investigated by the first–principle calculation,and calculated results indicate that title compounds possess the large birefringences about 0.123 and 0.135 for BPSS and BPSSe at 1?m,respectively,which indicate that they may be expected as potential IR birefringent materials.3.Four new quaternary chalcogenides with the formula of Na₆Zn₃M₂^IIIQ₉(M^III=Ga,In;Q=S,Se)have been successfully synthesized for the first time.They are isostructural and crystallize in the monoclinic C2/c space group.Seen from their structures,they exhibit two opposite direction layers composed of the interconnection of countless Zn/M₁₀Q₂₀ supertetrahedra?T₃-type?clusters,and then three coordination-type NaQ_n units?n=4-6?exist among the interlayers to bridge them together.Moreover,we have also systematically compared the structural differences of all the T₃-containing quaternary chalcogenides and the result shows that title compounds possess the shortest interlayer spacing and more tilting T₃ clusters-built layers in comparison with other related compounds.Measured optical properties indicate that their optical bandgaps are in the range from 2.22–3.15 eV,respectively.Photoluminescence result shows that title compounds have potential application prospect as blue and green light emitters in view of their obvious emission peaks centered at 463 and 541 nm.Electronic structures and density of states were also calculated by the first–principle calculations and the results indicate that their optical bandgaps are mainly determined by the T₃ clusters.