Chiral microporous rare-earth silico-germanates: Synthesis, structure and photoluminescence properties

The first examples of chiral microporous rare-earth silico-germanates were obtained by isomorphous substitution of Si4+ by Ge4+ in small-pore Na-3[RESi3O9]center dot 3H(2)O (RE = Y3+, Eu3+), using hydrothermal synthesis. Single-crystal X-ray diffraction and Si-29 solid-state NMR clearly demonstrate the framework insertion of Ge4+, with preference for two of the three crystallographic T4+ sites. The isomorphous Ge4+ for Si4+ substitution originates a dispersion of the RE3+ environments, resulting in multiple and broader Eu3+ emission lines. Despite these, the main photoluminescence properties of pure Si- and Ge,Si-materials are very similar. A particularly intriguing feature is the detection, in both cases, of quasi-enantiomeric domains by selective excitation at 12 K. (C) 2012 Elsevier Inc. All rights reserved.