Red and near-infrared emitting phosphors based on Eu3+- or Nd3+-doped lanthanum niobates prepared by the sol-gel route.

We have evaluated the structural and luminescence properties of Eu3+- or Nd3+-doped lanthanum niobate systems synthesized via a sol-gel route and containing different dopant contents. XRD analysis revealed that the orthorhombic La3NbO7 and monoclinic LaNbO4 crystalline phases were present in all the samples, regardless of the dopant concentration. The excitation spectra of the samples displayed a broad band due to Nb5+→O2- charge transfer; this band was quite sensitive to the increasing Eu3+ content. The photoluminescence emission spectra of the samples with a lower Eu3+ content showed that Eu3+ occupied both crystalline phases. However, when the Eu3+ content increased, these ions preferentially occupied the C2 symmetry sites in the LaNbO4 host lattice. There was no emission quenching for the Eu3+-doped samples with a Eu3+ content as high as 20 mol%. The emission spectra of the Nd3+-doped samples displayed an intense emission band in the NIR-II biological window under NIR-I excitation, at 808 nm. In the case of the samples with a lower Nd3+ content, Nd3+ occupied distinct symmetry sites in La3NbO7. In contrast, in the samples with a higher Nd3+ content, these ions preferentially occupied LaNbO4 sites. The Nd3+ concentration that quenched emission in the Nd3+-doped samples was about 2.6 mol%, due to Nd3+-Nd3+ cross-relaxation processes. On the basis of these findings, the Eu3+-doped samples explored herein have promising applications in the lighting field, whereas the Nd3+-doped samples have potential use as solid-state lasers and biomarkers.

Super Broadband at Telecom Wavelengths From RE3+-Doped SiO2-Ta2O5 Glass Ceramics Planar Waveguides.

This paper reports on the preparation of Er3+/Yb3+/Tm3+, Er3+/Yb3+/Nd3+, and Er3+/Tm3+/Nd3+ triply doped and Er3+-doped SiO2-Ta2O5 glass ceramic nanocomposites and active planar waveguides by the sol-gel process using the dip-coating technique as deposition method. The investigation of their structural, morphological, and luminescent properties using XRD, AFM, and photoluminescence analysis, are reported here. The XRD results showed the presence of L-Ta2O5 nanocrystals dispersed in the SiO2-based amorphous host for all the nanocomposites and films. The rare earth ion (RE3+) doping concentration affected both the crystallinity, and the crystallite sizes of the Ta2O5 dispersed into SiO2-Ta2O5 nanocomposites and waveguides. AFM characterization revealed crack free and smooth surface roughness and differences in viscoelasticity on the Er3+-doped SiO2-Ta2O5 films surface, which allows the identification of Ta2O5 nanocrystals on the SiO2 amorphous host. The Er3+ doped and triply doped SiO2-Ta2O5 nanocomposites displayed broad- and super broadband NIR emissions with a FWHM up to 173 nm achieved in the telecom wavelengths. The lifetime of the 4I13/2 emitting level of the Er3+-doped SiO2-Ta2O5 waveguides is strongly dependent on Er3+ concentration and an emission quenching was negligible up to 0.81 mol%. The structural and luminescent investigations indicated that RE3+-doped SiO2-Ta2O5 glass ceramics are promising candidates for photonic applications in optical devices operating in wide wavelengths at the telecom bands.