Polymorphism and photoluminescence properties of KErSiO.

Two polymorphs of tripotassium erbium disilicate, KErSiO, were synthesized by high-temperature flux crystal growth during the exploration of the flux technique for growing new alkali rare-earth elements (REE) containing silicates. Their crystal structures were determined by single-crystal X-ray diffraction analysis. One of them (denoted 1) crystallizes in the space group P6/mmc and is isostructural with disilicates KLuSiO, KScSiO and KYSiO, while the other (denoted 2) crystallizes in the space group P6/mcm and is isostructural with disilicates KNdSiO, KREESiO (REE = Gd-Yb), KYSiO, K(YDy)SiO and KSmSiO.

(3+1)-Incommensurately modulated crystal structure of Cs3ScSi6O15.

Single-crystal X-ray diffraction of Cs3ScSi6O15 shows the presence of main reflections and satellite reflections up to the fourth order along the c* direction. The (3+1)-dimensional incommensurately modulated structure was solved in superspace group X3m1(00gamma)0s0 [a = 13.861 (1), c = 6.