Multi-wavelength europium-based hybrid phosphors

A series of europium doped organic/inorganic hybrids prepared by the sol-gel process are investigated by photoluminescence and infrared spectroscopies. The matrix of the so-called ureasils is a siliceous network to which oligopolyoxyethylene chains containing about 40.5 oxyethylene units are grafted by means of urea cross-links. The Eu3+ ions have been incorporated as europium triflate. The FT-IR spectra reveal that the polyether chains become more disordered in the presence of the lanthanide salt and suggest that 'free' and coordinated triflate ions exist in the ureasils. The coordination of the Eu3+ ions by the carbonyl groups of the urea moieties is proposed. The luminescence spectra present a band between 400 and 700 nm, associated with the inorganic skeleton emission, and a series of Eu3+ lines with smaller widths assigned to the D-5(0) --> F-7(0-4) transitions. The local coordination of the cations in a continuous distribution of low symmetry similar sites is suggested. (C) 1999 Elsevier Science B.V. All rights reserved.