A new family of mixed anion cesium rare earth silicates exhibiting intense scintillation in several ranges of the visible spectrum are reported. CsRESiOF (RE = Y, Eu-Lu) have been synthesized using an enhanced flux growth method for the targeted growth of mixed anion systems. This is the first example of this method being used for the growth of oxyhalides. The compounds crystallize in the triclinic space group P1̅ with the lattice parameters a = 7.0832(2) Å, b = 7.1346(2) Å, c = 16.2121(5) Å, α = 95.8090(10)°, β = 90.0580(10)°, γ = 119.7650(10)° for the Tb analogue. The structure consists of REO and REOF polyhedra connected by SiO sheets with a previously unobserved silicate sheet topology that contains the uncommon cyclic SiO trimers. The synthesis, structure, magnetic and optical properties are reported including, notably, intense X-ray scintillation in CsTbSiOF.

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Single crystals of Cs6Ln2Ge11O28 (Ln = La, Pr, and Nd) and Cs12Bi3Ge24O58F were grown from a CsCl/CsF flux. These compounds crystallize in new structure types and are members of a new structural family related to the Wadeite structure by polyhedral substitution. Elucidation of this structural family, dubbed the superwadeites, allows for the prediction of the existence and structure of Cs2Ge5O11. Density functional theory calculations support that Cs2Ge5O11 is a stable compound. Ultimately, this compound is grown via a solid-state reaction, and its structure is refined via Rietveld refinement.

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Single crystals of 12 new cesium rare earth germanates crystallizing in two new structure types were grown from a CsCl/CsF flux. Cs3REGe3O9 (RE = Pr, Nd, and Sm–Yb), a new family of germanates that form for almost the entire series of rare earth elements, crystallizes in orthorhombic space group Pna21 with lattice parameters in the following ranges: a = 13.7033(4)–14.022(2) Å, b = 7.0545(2)–7.2405(12) Å, and c = 12.6672(4)–12.836(2) Å. Surprisingly, the Tb reaction yielded both Cs3TbGe3O9 and Cs8Tb3Ge9O27, a rare example of a mixed-valent Tb­(III)/Tb­(IV) compound. Cs8Tb3Ge9O27 crystallizes in space group P3 with the following lattice parameters: a = 11.2906(4) Å, and c = 7.9605(3) Å. The mixed-valent oxidation state of Tb was confirmed by structure solution, bond-valence sums, X-ray photoelectron spectroscopy data, and magnetic data. Optical and magnetic properties are reported for both sets of compounds.