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 [Cs6X]AGa6Q12 (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 [Cs6X]AGa6Q12 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–xRbxBr]RbGa6S12, which did not form during the direct flux crystal growth. Furthermore, single crystals of [Cs6X]AGa6Q12: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.