Coordination mechanism of cyanine dyes on the surface of core@active shell β-NaGdF4:Yb3+,Er3+ nanocrystals and its role in enhancing upconversion luminescence

The sensitization of lanthanide-doped upconversion nanocrystals (UCNCs) using organic dyes with a broad and intense optical absorption is an interesting approach for efficient excitation-energy harvesting and enhancing the upconversion luminescence of such UCNCs. In this work, an ultrasmall (similar to 6.5 nm in diameter) beta-NaGdF4:Yb3+,Er3+ core and related core@shell UCNCs were sensitized using six NIR-excitable cyanine dyes with a wide range of functional groups and optical properties. The greatest UC enhancement of 680-times was observed for the conjugate between the Cy 754 dye and NaGdF4:Yb3+,Er3+@NaGdF4:10%Yb3+,30%Nd3+ core@shell UCNCs excited using a 754 nm laser. The enhancement was estimated relative to NaGdF4:Yb3+,Er3+@NaGdF4:10%Yb3+,30%Nd3+ core@shell UCNCs capped with oleic acid and excited using a similar intensity (75 W cm(-2)) of a 980 nm laser. UC intensity measurements for identical dye-sensitized UCNCs carried out in methanol and in deuterated methanol under argon, as well as in air, allowed us to reveal the connection of the dye triplet states with UCNC sensitization as well as of the hydroxyl groups with quenching of the excited states of lanthanide ions. For UCNCs dispersed in methanol, the strong quenching UC luminescence was always observed, including core@shell UCNCs (with a shell of similar to 2 nm). A strong influence of the triplet states of the dyes was observed for the two dyes Cy 754 and Cy 792 that bind firmly to UCNCs and allow the distances between the dye and the UCNC to be reduced, whereas the contribution of this sensitization pathway is very insignificant for Cy 740 and Cy 784 dyes that bind weakly to UCNCs

Coordination mechanism of cyanine dyes on the surface of core@active shell β-NaGdF4_{4}:Yb3+^{3+},Er3+^{3+} nanocrystals and its role in enhancing upconversion luminescence

The sensitization of lanthanide-doped upconversion nanocrystals (UCNCs) using organic dyes with a broad and intense optical absorption is an interesting approach for efficient excitation-energy harvesting and enhancing the upconversion luminescence of such UCNCs. In this work, an ultrasmall (∼6.5 nm in diameter) β-NaGdF$_{4}$:Yb$^{3+}$,Er$^{3+}$ core and related core@shell UCNCs were sensitized using six NIR-excitable cyanine dyes with a wide range of functional groups and optical properties. The greatest UC enhancement of 680-times was observed for the conjugate between the Cy 754 dye and β-NaGdF$_{4}$:Yb$^{3+}$,Er$^{3+}$@NaGdF$_{4}$:10%Yb$^{3+},30$^{3+} core@shell UCNCs excited using a 754 nm laser. The enhancement was estimated relative to NaGdF$_{4}$:Yb$^{3+}$,Er$^{3+}$@NaGdF$_{4}$:10%Yb$^{3+},30$^{3+} core@shell UCNCs capped with oleic acid and excited using a similar intensity (75 W cm$^{-2}$) of a 980 nm laser. UC intensity measurements for identical dye-sensitized UCNCs carried out in methanol and in deuterated methanol under argon, as well as in air, allowed us to reveal the connection of the dye triplet states with UCNC sensitization as well as of the hydroxyl groups with quenching of the excited states of lanthanide ions. For UCNCs dispersed in methanol, the strong quenching UC luminescence was always observed, including core@shell UCNCs (with a shell of ∼2 nm). A strong influence of the triplet states of the dyes was observed for the two dyes Cy 754 and Cy 792 that bind firmly to UCNCs and allow the distances between the dye and the UCNC to be reduced, whereas the contribution of this sensitization pathway is very insignificant for Cy 740 and Cy 784 dyes that bind weakly to UCNCs

Interface Pattern Engineering in Core-Shell Upconverting Nanocrystals: Shedding Light on Critical Parameters and Consequences for the Photoluminescence Properties

Advances in controlling energy migration pathways in core-shell lanthanide (Ln)-based hetero-nanocrystals (HNCs) have relied heavily on assumptions about how optically active centers are distributed within individual HNCs. In this article, it is demonstrated that different types of interface patterns can be formed depending on shell growth conditions. Such interface patterns are not only identified but also characterized with spatial resolution ranging from the nanometer- to the atomic-scale. In the most favorable cases, atomic-scale resolved maps of individual particles are obtained. It is also demonstrated that, for the same type of core-shell architecture, the interface pattern can be engineered with thicknesses of just 1 nm up to several tens of nanometers. Total alloying between the core and shell domains is also possible when using ultra-small particles as seeds. Finally, with different types of interface patterns (same architecture and chemical composition of the core and shell domains) it is possible to modify the output color (yellow, red, and green-yellow) or change (improvement or degradation) the absolute upconversion quantum yield. The results presented in this article introduce an important paradigm shift and pave the way toward the emergence of a new generation of core-shell Ln-based HNCs with better control over their atomic-scale organization

Preventing cation intermixing enables 50% quantum yield in sub-15 nm short-wave infrared-emitting rare-earth based core-shell nanocrystals

Short-wave infrared (SWIR) fluorescence could become the new gold standard in optical imaging for biomedical applications due to important advantages such as lack of autofluorescence, weak photon absorption by blood and tissues, and reduced photon scattering coefficient. Therefore, contrary to the visible and NIR regions, tissues become translucent in the SWIR region. Nevertheless, the lack of bright and biocompatible probes is a key challenge that must be overcome to unlock the full potential of SWIR fluorescence. Although rare-earth-based core-shell nanocrystals appeared as promising SWIR probes, they suffer from limited photoluminescence quantum yield (PLQY). The lack of control over the atomic scale organization of such complex materials is one of the main barriers limiting their optical performance. Here, the growth of either homogeneous (α-NaYF$_4$) or heterogeneous (CaF$_2$) shell domains on optically-active α-NaYF$_4$:Yb:Er (with and without Ce$^{3+}$ co-doping) core nanocrystals is reported. The atomic scale organization can be controlled by preventing cation intermixing only in heterogeneous core-shell nanocrystals with a dramatic impact on the PLQY. The latter reached 50% at 60 mW/cm$^2$; one of the highest reported PLQY values for sub-15 nm nanocrystals. The most efficient nanocrystals were utilized for in vivo imaging above 1450 nm

Evaluation globale standardisée systématique des rhumatismes inflammatoires chroniques: intérêts et limites

Introduction: National and international recommendations call for an annual standardized systematic holistic review in the management of chronic inflammatory rheumatism (CIR). This includes an assessment of disease activity and severity, as well as patient education on the disease, knowledge of pharmacological and non-pharmacological treatments, adherence to treatment and screening for comorbidities. Our study aims to recall the definition of a holistic review (HR), to present the evidence of their effectiveness and to give an overview of HR practices in France. Methods: A literature review was conducted in the Pubmed database to identify randomized controlled trials (RCTs) or meta-analyses reporting the efficacy of a multidisciplinary intervention in ICR or other chronic diseases. Two online surveys were sent to all rheumatology departments in France and to a sample of independent rheumatologists, with 34 and 19 questions respectively. These questionnaires were used to determine the profile of the responding center/rheumatologist, the existence of an HR and the obstacles or facilitators to its implementation. Results: Literature search yielded 872 articles, 24 of which were finally included: 16 RCTs and 8 meta-analyses. Only 3 articles concerned ICRs, including one meta-analysis of 10 RCTs in rheumatoid arthritis (RA). Of these 3 studies, 2 RCTs in systemic lupus and systemic sclerosis showed a favorable impact of a multidisciplinary approach on SLEDAI and grip strength and mouth opening respectively, while the meta-analysis in RA showed no benefit on disability or disease activity.The questionnaire was answered by 72 centers and 186 rheumatologists. A third of the centers had already implemented a HR during an day hospitalization. 70 % of centers estimated that they managed more than 10 patients per month, devoting an average of 35 minutes of rheumatologist time and 90 minutes of cumulative time for all other healthcare professionals (HCPs) involved in the program. Most of the HCPs involved were nurses (92 %), dieticians (56 %) and physiotherapists (56 %). The main obstacles to setting up a HR were the lack of paramedical resources, lack of economic value and lack of support from treating rheumatologists, while patient motivation was seen as a facilitating factor. Conclusion: Although HR is recommended, there is little evidence of its effectiveness in ICR. Only 36 % of responding centers have implemented such a program. This survey helps to identify the obstacles and facilitators, and to find solutions for extending this practice

Prétraitement pyrochimique de flux chargés en produits de fission (mécanismes conduisant à l'obtention de phases cristallines en milieux chlorures fondus)

Le monde du nucléaire se prépare à de profondes modifications afin que l atome puisse prétendre au titre d énergie durable: c est ce que l on appelle le développement des systèmes nucléaires de 4e génération. Ainsi, les nouvelles techniques de retraitement pyrochimique des combustibles irradiés en milieux chlorures fondus génèrent des flux de déchet ultime que l on ne peut vitrifier. En raison de leur forte solubilité dans l eau, ils doivent être conditionnés sous une nouvelle forme chimique, compatible avec un stockage à long terme. Ce travail de thèse consiste à étudier de nouvelles voies pour la gestion des flux chlorés chargés en produits de fission (PF). Pour ce faire, une stratégie d extraction sélective PF via la formation in situ de phases cristallines a été retenue. La possibilité d extraire les terres rares en milieu eutectique LiCl-KCl a été démontrée via la mise au point d une nouvelle voie de synthèse de phosphates de terres rares (TRPO4). En ce qui concerne les alcalino-terreux, la conversion des chlorures de strontium et baryum en tungstate ou molybdate a été étudiée dans divers solvants. Les mécanismes réactionnels conduisant à l obtention de ces phases cristallines ont été étudiés via le couplage de techniques RMN et DRX. Il a tout d abord, été montré que ces mécanismes sont dépendants de la stabilité des précurseurs utilisés. Ainsi dans le cas de la formation des phosphates de terres rares le solvant s est révélé être chimiquement actif. En revanche, dans le cas de la formation de tungstates alcalino-terreux, il semblerait que le solvant joue le rôle d agent structurant pouvant ainsi contrôler la réactivité des solutésThe world of the nuclear power gets ready for profound modifications so that " the atom " can aspire in conformance with long-lasting energy: it is what we call the development of generation IV nuclear systems. So, the new pyrochemical separation processes for the spent fuel reprocessing are currently being investigated. Techniques in molten chloride media generate an ultimate flow (with a high chlorine content) which cannot be incorporated in conventional glass matrices. This flow is entirely water-soluble and must be conditioned in a chemical form which is compatible with a long-term disposal. This work of thesis consists in studying new ways for the management of the chlorinated streams loaded with fission products (FP). To do it, a strategy of selective FP extraction via the in situ formation of crystalline phases was retained. The possibility of extracting rare earths in the eutectic LiCl-KCl was demonstrated via the development of a new way of synthesis of rare earth phosphates (TRPO4).As regards alkaline earths, the conversion of strontium and barium chlorides to the corresponding tungstates or molybdates was studied in different solvents. Mechanisms leading to the crystalline phases in molten chloride media were studied via the coupling of NMR and XRD techniques. First of all, it has been shown that these mechanisms are dependent on the stability of the used precursors. So in the case of the formation of rare earth phosphates the solvent is chemically active. On the other hand, in the case of the formation of alkaline earth tungstates it would seem that the solvent plays the role of structuring agent which can control the ability to react of chloridesNANTES-BU Sciences (441092104) / SudocSudocFranceF

High-temperature and melting behaviour of nanocrystalline refractory compounds: an experimental approach applied to thorium dioxide.

Pioneering a so far unexplored research field, the behaviour from 1500 K up to melting of nanocrystalline (nc) thorium dioxide, the refractory binary oxide with the highest melting point (3651 K), was explored here for the first time using fast laser heating, multi-wavelength pyrometry and Raman spectroscopy for the analysis of samples quenched to room temperature. Nc-ThO2 was melted at temperatures hundreds of K below the melting temperature assessed for bulk thorium dioxide. A particular behaviour has been observed in the formed liquid and its co-existence with a partially restructured solid, possibly due to the metastable nature of the liquid itself. Raman spectroscopy was used to characterize the thermal-induced structural evolution of nc-ThO2. Assessment of a semi-empirical relation between the Raman active T2g mode peak characteristics (peak width and frequency) and crystallites size provided a powerful, fast and non-destructive tool to determine local crystallites growth within the nc-ThO2 samples before and after melting. This semi-quantitative analysis, partly based on a phonon-confinement model, constitutes an advantageous, more flexible, complementary approach to Electron Microscopy and Powder X-ray Diffraction for the crystallite size determination. The adopted experimental approach (laser heating coupled with Raman spectroscopy) is therefore proven to be a promising methodology for the high temperature investigation of nanostructured refractory oxides.JRC.E.3-Materials researc

Controlled Synthesis of Thorium and Uranium Oxide Nanocrystals

Very little is known about the size and shape effects on the properties of actinide compounds. As a consequence, the controlled synthesis of well-defined actinide-based nanocrystals constitutes a fundamental step before studying their corresponding properties. In this paper, we report on the non-aqueous surfactant-assisted synthesis of thorium and uranium oxide nanocrystals. The final characteristics of thorium and uranium oxide nanocrystals can be easily tuned by controlling a few experimental parameters such as the nature of the actinide precursor and the composition of the organic system (e.g., the chemical nature of the surfactants and their relative concentrations). Additionally, the influence of these parameters on the outcome of the synthesis is highly dependent on the nature of the actinide element (thorium versus uranium). By using optimised experimental conditions, monodisperse isotropic uranium oxide nanocrystals with different sizes (4.5 and 10.7 nm) as well as branched nanocrystals (overall size ca. 5 nm), nanodots (ca. 4 nm) and nanorods (with ultra-small diameters of 1 nm) of thorium oxide were synthesised.JRC.E.5-Nuclear chemistr