Tunable Salt-Inclusion Chalcogenides for Ion Exchange, Photoluminescence, and Scintillation

Abstract

Salt-inclusion chalcogenides (SICs) consisting of covalent and ionic building blocks have emerged as functional materials exhibiting novel topologies that result from the combination of the chalcogenide-based frameworks and the salt inclusions contained within them. Nine compositions of a novel family of SICs [Cs6 X]AGa6 Q 12 (A = Na, K, and Rb; X = F, Cl, and Br; Q = S and Se) were synthesized via halide/polychalcogenide flux crystal growth and structurally characterized. Ex situ powder X-ray diffraction analysis was used to determine the optimal synthesis temperatures at which the titled SIC materials crystallized in the flux. Density functional theory calculations coupled with convex hull construction were performed to predict the stability of [Cs6 X]AGa6 Q 12 compositions as a function of X, A, and Q and to identify their decomposition pathways. A combination of single-crystal X-ray diffraction and energy-dispersive spectroscopy was used to study single-crystal-to-single-crystal (SC-SC) ion-exchange-reaction, a process that also allowed for the synthesis of two additional members of this family, [Cs6F]NaGa6S12 and [Cs6–x Rb x Br]RbGa6S12, which did not form during the direct flux crystal growth. Furthermore, single crystals of [Cs6 X]AGa6 Q 12:Mn2+ were obtained through direct flux crystal growth and SC-SC ion-exchange reactions and studied for their photoluminescent behavior using individual single crystals. The emission profile changed as a function of Mn2+-content, the A cation identity, and the synthesis method used. Finally, radioluminescence measurements were carried out on [Cs6Cl]NaGa6S12:Mn2+ bulk samples, resulting in bright orange scintillation.

Advances in Chalcogenide Crystal Growth: Flux and Solution Syntheses, and Approaches for Postsynthetic Modifications

“…(left) Schematic classification of salt-inclusion materials by covalent and ionic framework dimensionality. (right) Examples of hybrid materials with 0D-0D, [Cs 6 Cl] 2 Cs 5 Ga 15 Ge 9 Se 48 , 2D-2D, [Na 2 Cl]­Ga Q 2 , 2D-0D, [Cs 6 X ] A Ga 6 Q 12 , frameworks and salt-inclusion fragment dimensionalities, respectively. Gray and green shapes represent covalent and ionic moieties, respectively.…”

“…Therefore, this study revealed a novel synthetic route for obtaining new compositions of SIC materials that cannot be synthesized through the traditional synthetic pathway, highlighting that SCSC transformation generally increases the stabilization range for the kinetic products. Furthermore, complete SCSC anion exchange and partial cation exchange were demonstrated in the example of the [Cs 6 X ] A Ga 6 Q 12 (X = F, Cl, and Br; A = Na, K, and Rb; Q = S and Se) SIC family consisting of a 2D framework and a 0D salt-inclusion moiety, [Cs 6 X ] 5+ . The interesting result was the formation of the fluoride-based SIC [Cs 6 F]­NaGa 6 S 12 via postsynthetic modification of [Cs 6 Cl]­NaGa 6 S 12 using an CsF/CsI flux at 600 °C .…”

“…Furthermore, complete SCSC anion exchange and partial cation exchange were demonstrated in the example of the [Cs 6 X ] A Ga 6 Q 12 (X = F, Cl, and Br; A = Na, K, and Rb; Q = S and Se) SIC family consisting of a 2D framework and a 0D salt-inclusion moiety, [Cs 6 X ] 5+ . The interesting result was the formation of the fluoride-based SIC [Cs 6 F]­NaGa 6 S 12 via postsynthetic modification of [Cs 6 Cl]­NaGa 6 S 12 using an CsF/CsI flux at 600 °C . Such a transformation was only possible due to the use of a double container: a crimped silver tube sealed inside a fused silica tube; otherwise, the fluoride flux would react with the fused silica.…”

Flux-assisted polytypism in the [Na2Cl]GaQ2 heterolayered salt-inclusion chalcogenide family

“…30 Another example is the [Cs 6 X]AGa 6 Q 12 family consisting of 0D Cs 6 X and 2D gallium chalcogenide units. 31 Heterolayered compositions are structurally similar to salt-inclusion materials, as separate layers may be constructed from cation- and anion-centered polyhedra. For example, in [MO]CuQ (M = Bi and La; Q = S, Se, and Te), where the layered slabs consist of OM 4 and CuQ 4 tetrahedra.…”

“…We were not able to obtain the [Na 2 Br]GaS 2 analog; changing NaCl to NaBr in the synthesis resulted in the formation of NaGaS 2 . Moreover, we probed ion-exchange reactions that previously demonstrated strong potential as being one synthetic approach for obtaining new compositions of 0D salt-inclusion materials that cannot be prepared directly; 31 however, our attempts to synthesize [Na 2 Br]GaS 2 (see ESI† for more information) using this approach did not succeed. In summary, the t -[Na 2 Cl]GaS 2 composition is the most stable of the t -[A 2 X]GaS 2 (A = Li, Na, and K; X = F, Cl, and Br) compositions based on their decomposition enthalpies (Fig.…”