Broadband NIR emission in sol-gel Er(3+)-activated SiO2-Ta2O5 glass ceramic planar and channel waveguides for optical application.

An Er(3+)-doped SiO2:Ta2O5 optical channel waveguide and nanocomposite were prepared by the sol-gel route at a Si:Ta 50:50 molar ratio. Channels with an excellent surface profile were easily and quickly fabricated by focusing a femtosecond laser onto the surface of multilayered films deposited on SiO2/Si substrates. In parallel, the same sol used to prepare the film was annealed at 900, 1000, and 1100 degrees C for 2 h, to get the nanocomposite materials. A broadband NIR emission around 1538 nm, assigned to the 4I13/2 --> 4I15/2 transition of the Er3+ ions was observed in the nanocomposites of amorphous SiO2 containing dispersed Ta2O5 nanocrystals. The 4I13/2 lifetime and emission bandwidth depend on the annealing temperature. In conclusion, Er(3+)-doped SiO2:Ta2O5 channel waveguides and nanocomposites are promising materials for photonic applications.

Enhanced Eu3+ emission in aqueous phosphotungstate colloidal systems: stabilization of polyoxometalate nanostructures.

Luminescent Eu(3+)-containing polyphosphate-tungstate aqueous colloidal systems were prepared and studied as a function of the relative polyphosphate-tungstate content. In polyphosphate-rich solutions, Eu(3+) ions occupy cagelike sites composed of phosphate groups from the metaphosphate chains. In these sites, an average number of 0.5 water molecule coordinates to an Eu(3+) ion and the (5)D(0) emission quantum efficiency is 0.22. Tungstate addition leads to important modifications in neighboring Eu(3+) leading to coordination sites in the aqueous medium where metal ions are completely hidden from interactions with solvent molecules. Transmission electron microscopy results clearly show W-rich nanoparticles with sizes between 5 and 10 nm for all tungstate relative concentrations. For high tungstate relative contents (above 30 mol %), spectroscopic results suggest the presence of Eu(3+) in polyoxometalate (POM)-like sites by comparison with the well-known decatungstoeuropate [EuW(10)O(36)](9-) structure. These new aqueous colloids display surprisingly high (5)D(0) emission quantum efficiencies of ca 80% because of the strong ligand field provided by tungstate POM ligands and the complete absence of water molecules from the Eu(3+) first coordination shell.