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Coupling effects of localized surface plasmon resonance (LSPR) represent an efficient means to tune the plasmonic modes and to enhance the near-field. While LSPR coupling in metal nanoparticles has been extensively explored, limited attention has been given to heavily doped semiconductor nanocrystals. Here, we investigate the LSPR coupling behavior of Cs-doped tungsten oxide (Cs x WO 3-δ ) nanocrystal platelets as they undergo an oriented assembly into parallel stacks. The oriented assembly was achieved by lowering the dispersion stability of the colloidal nanoplatelets, of which the basal surface was selectively ligand-functionalized. This assembly induces simultaneous blue-shifts and red-shifts of dual-mode LSPR peaks without compromising the intensity and quality factor. This stands in contrast to the significant damping, broadening, and overall red-shift of the LSPR observed in random assemblies. Computational simulations successfully replicate the experimental observations, affirming the potential of this coupling phenomenon of near-infrared dual-mode LSPR in diverse applications including solar energy, bio-optics, imaging, and telecommunications.

A small library of amphiphilic prodrugs has been synthesized by conjugation of gemcitabine (Gem) (a hydrophilic nucleoside analogue) to a series of lipid moieties and investigated for their capacity to spontaneously self-assemble into nanosized objects by simple nanoprecipitation. Four of these conjugates formed stable nanoparticles (NPs), while with the others, immediate aggregation occurred, whatever the tested experimental conditions. Whether such capacity could have been predicted based on the prodrug physicochemical features was a matter of question. Among various parameters, the hydrophilic-lipophilic balance (HLB) value seemed to hold a predictive character. Indeed, we identified a threshold value which well correlated with the tendency (or not) of the synthesized prodrugs to form stable nanoparticles. Such a hypothesis was further confirmed by broadening the analysis to Gem and other nucleoside prodrugs already described in the literature. We also observed that, in the case of Gem prodrugs, the lipid moiety affected not only the colloidal properties but also the in vitro anticancer efficacy of the resulting nanoparticles. Overall, this study provides a useful demonstration of the predictive potential of the HLB value for lipid prodrug NP formulation and highlights the need of their opportune in vitro screening, as optimal drug loading does not always translate in an efficient biological activity.

Rare-earth-doped oxides are a class of compounds that have been largely studied in the context of the development of luminescent nanocrystals for various applications including fluorescent labels for bioimaging, MRI contrast agents, luminescent nanocomposite coatings, etc. Elaboration of colloidal suspensions is usually achieved through coprecipitation. Particles exhibit emission properties that are similar to the bulk counterparts, although altered by crystalline defects or surface quenching species. Focusing on YVO 4 :Eu, one of the first reported systems, the aim of this work is to revisit the elaboration of nanoparticles obtained through a simple aqueous coprecipitation route. The objective is more precisely to get a better understanding of the parameters affecting the particles' internal microstructure, a feature that is poorly controlled and characterized. We show that the hydroxyl concentration in the precursor solution has a drastic effect on the particles' microstructure. Moreover, discrepancies in the reported particle structure are shown to possibly arise from the carbonation of the strongly basic orthovanadate precursor. For this study, SAXS/WAXS is shown to be a powerful tool to characterize the multiscale structure of the particles. It could be shown that playing on the precursor composition, it may be varied between almost monocrystalline nanocrystals to particles exhibiting a hierarchical microstructure well described by a surface fractal model. This work provides a new methodology for the characterization of nanoparticles microstructure and opens new directions for its optimization in view of applications.

Lanthanide elements exhibit highly appealing spectroscopic properties that are extensively used for phosphor applications. Their luminescence contains precise information on the internal structure of the host materials. Especially, the polarization behavior of the transition sublevel peaks is a fingerprint of the crystal phase, symmetry, and defects. However, this unique feature is poorly explored in current research on lanthanide nanophosphors. We here report on a detailed investigation of the evolution of Eu 3+ luminescence during the thermally induced phase transition of LaPO 4 nanocrystal hosts. By means of c-axis-aligned nanocrystal assemblies, we demonstrate a dramatic change of the emission polarization feature corresponding to the distinct Eu 3+ site symmetries in different LaPO 4 polymorphs. We also show that changes of the nanocrystal structure can be identified by this spectroscopic method, with a much higher sensitivity than the X-ray diffraction analysis. This new insight into the nanostructure-luminescence relationship, associated with the unprecedented polarization characterizations, provides a new methodology to investigate phase transitions in nanomaterials. It also suggests a novel function of lanthanide emitters as orientation-sensing nanoprobes for innovative applications such as in bioimaging or microfluidics.

Crystalline rare earth fluoride nanoparticles were synthesized by reacting rare earth ions with charge-transfer complexes, in solution, under mild conditions. An infrared study showed that these intermediate complexes are made up of solvent molecules (amide: N,N-dimethylformamide, 1-methyl-2-pyrrolidinone, etc.) and fluoride ions coming from hydrofluoric acid. The size and shape of the particles can be controlled through the process parameters. The complete study of the particles obtained through this process is carried out in this document, especially for the YbF(3) system. However, the process can easily be extended to the whole series of rare earth elements. We also show the ability of these objects to be transferred from an aqueous medium to an organic phase thanks to their surface modification. Finally, transparent monolithic xerogels of rare earth fluoride have been developed starting from the prepared colloidal solutions.