Local Er(iii) environment in luminescent titanosilicates prepared from microporous precursorsElectronic supplementary information (ESI) available: Er LIII-edge k3-weighted EXAFS spectra and Fourier transforms. See http://www.rsc.org/suppdata/jm/b1/b107136j/

Abstract

The local environment of Er3+ ions in microporous titanosilicate ETS-10 and in synthetic narsarsukite and glassy materials obtained by calcination of ETS-10 has been investigated by EXAFS, Raman and photoluminescence spectroscopies. Er LIII-edge EXAFS studies of Er3+-doped ETS-10 support the view that the exchanged Er3+ ions reside close to the (negatively charged) TiO6 octahedra. In ETS-10, Er3+ is partially bonded to framework oxygen atoms and hydration water molecules. The Er⋯Ti distance (3.3 A) is similar to the Na⋯Ti distances (3.15–3.20 A) reported previously for Na–ETS-10. Although the exact location of the ErO6 units within the host structure of Er3+-doped synthetic narsarsukite is still an open question, it is most likely that Er3+ substitutes Ti4+ rather than Na+ ions. EXAFS spectroscopy indicates that no significant clustering of erbium atoms occurs in the titanosilicate samples studied. Evidence for the insertion of Er3+ ions in the framework of narsarsukite has been obtained by Raman spectroscopy. This is indicated by the increasing full-width at half-maximum (FWHM) of the 775 cm−1 peak and the increasing intensity of the anatase peaks as the erbium content increases. In addition, as the narsarsukite Er3+ content increases a band at ca. 515 cm−1 firstly broadens and subsequently a new peak appears at ca. 507 cm−1. Er3+-doped narsarsukite exhibits a characteristic local vibrational frequency, ħωca. 330 cm−1, with an electron–phonon coupling, gca. 0.2, which constitutes additional evidence for framework Er3+ insertion. The number of lines in the infrared emission spectrum of synthetic narsarsukite indicates the presence of two optically-active erbium centres with very similar local environments and an average 4I13/2 lifetime of 7.8 ± 0.2 ms.