“…Multinary chalcogenide semiconductors are multifunctional materials with diverse chemical and physical properties and are promising for various technological applications. Among this class of solids, quaternary chalcogenide materials A a M b M c ′ Q d ( A = alkali metal, thallium; M = group 13 metal; M ′ = group 14 metal; Q = chalcogen) feature a covalently bonded anionic framework of [ M b M c ′ Q d ] a − of any dimensionality, that is, one-dimensional (1D), two-dimensional (2D), or three-dimensional (3D), and charge balancing alkali cations. − Prominent examples of these properties are the strong nonlinear optical (NLO) second-harmonic generation (SHG) of noncentrosymmetric materials such as LiGaGe 2 Q 6 , − A 2 In 2 M ′ Q 6 , − and TlGaSn 2 Q 6 . − A series of centrosymmetric A Ga M ′ Q 4 ( A = K, Rb, Cs, Tl; M ′ = Si; Ge, Sn; Q = S, Se) polymorphs were reported to exhibit a high NLO third-harmonic generation scaling inversely with their band gaps following a power-law behavior. ,,,,− Among 3D quaternary chalcogenides, the chalcopyrite materials such as Cu(In,Ga)Se 2 , Cu(In,Ga) (S, Se) 2 , and Cu 2 ZnSnS 4 are currently of great interest as promising photovoltaics. − While the covalent anionic frameworks have optoelectronic functionalities depending on their composition and structure, the alkali metal counterions also represent chemical functionality because they often can be exchanged for other cations, thereby modifying the chemical composition. The so-called KMS family is a special subclass with a layered structure and remarkable ion-exchange properties relevant to environmental remediation. ,− This family is defined as A x [ M x Sn 3– x S 6 ], M being a divalent or trivalent metal .…”
RbInSn 2 S 6 and CsInSn 2 S 6 are yellow two-dimensional (2D) semiconductors featuring anionic SnS 2 -type layers of edge-sharing (In/Sn)S 6 octahedra. These structures are directly derived from the parent structure of SnS 2 by replacement of Sn 4+ atoms with A + and In 3+ atoms. The compounds crystallize, isotypic to the ion-exchange material KInSn 2 S 6 . They adopt the triclinic space group R3̅ m (no. 166). The compounds have similar indirect optical band gaps of 2.31(5) eV for Rb and 2.47(5) eV Cs. The measured work functions for each material are ∼5.38 eV. The density functional theory-calculated effective mass values exhibit strong anisotropy due to the 2D nature of the crystal structures and in the case of CsInSn 2 S 6 for hole carriers along the a, b, and c crystallographic directions are 0.30 m 0 , 0.34 m 0 , and 2.54 m 0 , respectively, while for electrons are 0.06 m 0 , 0.07 m 0 , and 0.47 m 0 , respectively.
“…Multinary chalcogenide semiconductors are multifunctional materials with diverse chemical and physical properties and are promising for various technological applications. Among this class of solids, quaternary chalcogenide materials A a M b M c ′ Q d ( A = alkali metal, thallium; M = group 13 metal; M ′ = group 14 metal; Q = chalcogen) feature a covalently bonded anionic framework of [ M b M c ′ Q d ] a − of any dimensionality, that is, one-dimensional (1D), two-dimensional (2D), or three-dimensional (3D), and charge balancing alkali cations. − Prominent examples of these properties are the strong nonlinear optical (NLO) second-harmonic generation (SHG) of noncentrosymmetric materials such as LiGaGe 2 Q 6 , − A 2 In 2 M ′ Q 6 , − and TlGaSn 2 Q 6 . − A series of centrosymmetric A Ga M ′ Q 4 ( A = K, Rb, Cs, Tl; M ′ = Si; Ge, Sn; Q = S, Se) polymorphs were reported to exhibit a high NLO third-harmonic generation scaling inversely with their band gaps following a power-law behavior. ,,,,− Among 3D quaternary chalcogenides, the chalcopyrite materials such as Cu(In,Ga)Se 2 , Cu(In,Ga) (S, Se) 2 , and Cu 2 ZnSnS 4 are currently of great interest as promising photovoltaics. − While the covalent anionic frameworks have optoelectronic functionalities depending on their composition and structure, the alkali metal counterions also represent chemical functionality because they often can be exchanged for other cations, thereby modifying the chemical composition. The so-called KMS family is a special subclass with a layered structure and remarkable ion-exchange properties relevant to environmental remediation. ,− This family is defined as A x [ M x Sn 3– x S 6 ], M being a divalent or trivalent metal .…”
RbInSn 2 S 6 and CsInSn 2 S 6 are yellow two-dimensional (2D) semiconductors featuring anionic SnS 2 -type layers of edge-sharing (In/Sn)S 6 octahedra. These structures are directly derived from the parent structure of SnS 2 by replacement of Sn 4+ atoms with A + and In 3+ atoms. The compounds crystallize, isotypic to the ion-exchange material KInSn 2 S 6 . They adopt the triclinic space group R3̅ m (no. 166). The compounds have similar indirect optical band gaps of 2.31(5) eV for Rb and 2.47(5) eV Cs. The measured work functions for each material are ∼5.38 eV. The density functional theory-calculated effective mass values exhibit strong anisotropy due to the 2D nature of the crystal structures and in the case of CsInSn 2 S 6 for hole carriers along the a, b, and c crystallographic directions are 0.30 m 0 , 0.34 m 0 , and 2.54 m 0 , respectively, while for electrons are 0.06 m 0 , 0.07 m 0 , and 0.47 m 0 , respectively.
“…The sharp rise in the edge becomes more pronounced with increasing photon energies, exposing strong absorption up to approximately 11 eV. Within this energy range, the alpha function exhibits several distinct fine-structure characteristics attributed to various electronic transitions [ 46 ]. Fig.…”
“…Multinary chalcogenide semiconductors are a highly interesting class of materials because of their diverse optical properties. Among these, the quaternary compounds A a M b M′ c Q d (A = alkali metal, thallium; M = group 13 metal; M′ = group 14 metal; Q = chalcogen) can exhibit strong nonlinear optical (NLO) second-harmonic generation (SHG) of noncentrosymmetric compounds like LiGaGe 2 Q 6 , − A 2 In 2 M′Q 6 , − and TlGaSn 2 Q 6 . − The centrosymmetric AGaM′Q 4 (A = K, Rb, Cs, Tl; M′ = Si; Ge, Sn; Q = S, Se) phases have been reported to have high nonlinear optical (NLO) third-harmonic generation (THG) properties scaling inversely with the band gaps following a power-law behavior . KInSn 2 S 6 is capable of fast ion exchange for the capture of lanthanide ions .…”
2− ) have been prepared by solid-state syntheses and structurally characterized by single-crystal X-ray diffraction techniques. These new phases fill in the missing links in these quaternary systems and crystallize in various two-dimensional layered polymorphs, while combinations containing large M 3+ and M′ 4+ cations also adopt an extended three-dimensional (3D) network structure. The AMM′Q 4 materials exhibit a wide range of band gaps with colored selenides (1.8 eV < E g < 2.3 eV) and mostly white sulfides (2.5 eV < E g < 3.6 eV). These phases have direct band gaps except for the thallium analogues and the cubic AGaSnSe 4 -cP84. First-principles theoretical calculations of the electronic band structures reveal critical insight into the structure/property relationships of these materials. The distinct polymorphism of these quaternary phases is studied by discussing kinetic and thermodynamic factors responsible for the crystallization, structural considerations, and complementary density functional theory (DFT) calculations.
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