Synthesis, crystal structure and luminescence properties of novel microporous europium silicate HK6Eu3+[Si10O25] with a framework formed of nano-scale tubes

Single crystals of new microporous europium and potassium silicate were synthesized using hydrothermal techniques and structure was determined. Monoclinic unit-cell values are: a = 27.6960(3), b = 7.0504(1), c = 14.2190(2) angstrom, beta = 116.306(1)degrees, space group 0/c. Structure model was determined by direct methods and refined up to R = 4.4% in anisotropic approximation. The compound HK6Eu3+[Si10O25] crystallizes in a new structure type that is based on nano-scale oval tubes of eight-member rings Si8O24] with inner diameters of 1.7 and 3.4 angstrom joint by additional Si-tetrahedra. Despite of the fact that the inner diameter of tubes is very small they are not empty. Symmetrical H-bonds are formed between oxygen atoms along short diameters of the corrugated eight-member rings. Spectral characteristics of luminescence were determined. Low quantum yield with high element content and long kinetic attenuation show that minor number of Eu atoms is in "luminescent" state. The wide weak resolved lines of D-5(0) -> F-7(1) transition point to considerable disorder variation of Eu3+ surrounding. (C) 2013 Elsevier Inc. All rights reserved.