abstract
The hydrothermal synthesis and structural characterization of the lanthanide silicate system [Na(6)Ln(2)Si(12)O(30)center dot xH(2)O] (Ln=La(3+), Sm(3+), Eu(3+), Gd(3+), and Tb(3+)), named AV-21, has been reported. Structural elucidation of the Sm(3+) analogue (isomorphous with the Eu(3+), Gd(3+), and Tb(3+) frameworks) using single-crystal synchrotron X-ray diffraction and solid-state NMR spectroscopy reveal disorder in the Si(1) second coordination sphere. La-AV-21 presents a distinct framework. These materials combine microporosity and interesting photoluminescence features with structural flexibility that allows the introduction of a second or third type of lanthanide center. Room-temperature lifetime decay dynamics have been used to estimate the Ln(3+)-Ln(3+) distances and the maximum distance over which energy transfer is active. Though the majority of Ln(3+) centers occupy regular framework positions, the Ln(2) defect centers are disordered over the Na(1) sites in the pores and greatly influence the energy-transfer process, providing a unique opportunity for studying the relationship between structural disorder and photoluminescence properties in framework solids.
keywords
EFFECTIVE IONIC-RADII; ENERGY-TRANSFER; PHASE-TRANSITIONS; CERIUM SILICATE; LUMINESCENCE; CRYSTAL; EUROPIUM; K3NDSI6O15-CENTER-DOT-XH(2)O; CONDUCTIVITY; COMPLEXES
subject category
Chemistry
authors
Kowalchuk, CM; Paz, FAA; Ananias, D; Pattison, P; Carlos, LD; Rocha, J
our authors
Duarte Ananias
Assistant Researcher
Filipe Alexandre Almeida Paz
Principal Researcher
João Rocha
Full Professor
Luís Carlos
Full professoracknowledgements
We are grateful to the Fundacao para a Ciencia e a Tecnologia (FCT, Portugal), FEDER, PTDC, and FAME NOE for the financial support. We also thank the ESRF (France, Grenoble) for allowing access to the Swiss-Norwegian BM01a beam line. C.M.K. thanks FCT for a Post Doctoral scholarship (SFRH/BPD/21039/2004).