The luminescence properties of colloidal YVO4:Eu nanoparticles (8 nm in diameter) are investigated and compared to those of the bulk materials. The emission quantum yield of nanoparticles is improved after the transfer of the colloidal particles into D2O, showing that surface OH groups act as efficient quenchers of the Eu3+ emission. The growth of a silicate shell around the nanoparticles decreases the optimum europium concentration, showing that energy transfers within the nanoparticles are limited by the quenching of the excited states of the vanadate groups. Nanoparticles also exhibit structural distortions directly related to the small size of the particles. No clear evidence is found concerning the influence of these distortions on the energy-transfer processes, since the improvement of the emission properties observed after thermal annealing of both crude and silicated powders seems to result mainly from the elimination of Eu3+ and vanadate quenchers from the surface. This latter effect is greatly enhanced in the presence of the silicate shell compared to bare particles.

We present a new process for the synthesis of colloidal europium-doped yttrium vanadate with a particle diameter of about 10 nm. Nanocrystals are produced by precipitation of citrate complexes of rare-earth salts with sodium orthovanadate. NMR and IR studies show that the interaction between citrate ligands and lanthanide ions limits the growth of particles and ensures the stability of the colloidal solutions through electrostatic and steric repulsions. The optimized process leads to stable and highly concentrated transparent colloidal solutions in water (up to 400 g·L-1).

Lanthanide ion-doped oxide nanoparticles were functionalized for use as fluorescent biological labels. These nanoparticles are synthesized directly in water, which facilitates their functionalization, and are remarkably photostable without emission intermittency. Nanoparticles functionalized with guanidinium groups act as artificial toxins and specifically target sodium channels. They are individually detectable in live cardiac myocytes, revealing a heterogeneous distribution of sodium channels. Functionalized oxide nanoparticles appear to be a novel tool that is particularly attractive for long-term single-molecule tracking.

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Lanthanide phosphate nanocrystals exhibiting the rhabdophane-type structure and mean particle sizes below 10 nm are synthesized by hydrolysis of an aqueous mixture of sodium tripolyphosphate (Na5P3O10) and lanthanide salts. 31P NMR studies show that polyphosphate groups act both as a source of orthophosphate and as complexing agents to, respectively, crystallize and stabilize LnPO4·xH2O (x ≈ 0.7) nanoparticles. In the ternary system (Ln = La, Ce, and Tb), polyphosphate-capped particles form well-dispersed and highly luminescent aqueous colloids which are promising for applications in light-emitting devices.

Octahedral molecular sieves (OMS) are built of transition metal-oxygen octahedra that delimit sub-nanoscale cavities. Compared to other microporous solids, OMS exhibit larger versatility in properties, provided by various redox states and magnetic behaviors of transition metals. Hence, OMS offer opportunities in electrochemical energy harnessing devices, including batteries, electrochemical capacitors and electrochromic systems, provided two conditions are met: fast exchange of ions in the micropores and stability upon exchange. Here we unveil a novel OMS hexagonal polymorph of tungsten oxide called h’-WO3, built of (WO6)6 tunnel cavities. h’-WO3 is prepared by a one-step soft chemistry aqueous route leading to the hydrogen bronze h’-H0.07WO3. Gentle heating results in h’-WO3 with framework retention. The material exhibits an unusual combination of 1-dimensional crystal structure and 2-dimensional nanostructure that enhances and fastens proton (de)insertion for stable electrochromic devices. This discovery paves the way to a new family of mixed valence functional materials with tunable behaviors.

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The core/shell strategy has been successfully developed for rhabdophane lanthanide phosphate aqueous colloids. The growth of a LaPO4‐xH2O shell around Ce,Tb‐doped core nanoparticles increases their stability against oxidation. A bright green luminescence is thus preserved in sol–gel films whose fabrication requires silica coating and thermal treatment of the core/shell nanoparticles.