Facile and rapid synthesis of highly luminescent nanoparticles via Pulsed Laser Ablation in Liquid

This paper demonstrates the usefulness of pulsed laser ablation in liquids as a fast screening synthesis method able to prepare even complex compositions at the nanoscale. Nanoparticles of Y2O3:Eu3+, Lu2O2S: Eu3+, Gd2SiO5:Ce3+ and Lu3TaO7:Gd3+,Tb3+ are successfully synthesized by pulsed laser ablation in liquids. The phase and stoichiometries of the original materials are preserved while the sizes are reduced down to 5-10 nm. The optical properties of the materials are also preserved but show some small variations and some additional structures which are attributed to the specificities of the nanoscale (internal pressure, inhomogeneous broadening, surface states...

Shells of crystal field symmetries evidenced in oxide nano-crystals

By the use of a point charge model based on the Judd-Ofelt transition theory, the luminescence from Eu3+ ions embedded in Gd2O3 clusters is calculated and compared to the experimental data. The main result of the numerical study is that without invoking any other mechanisms such as crystal disorder, the pure geometrical argument of the symmetry breaking induced by the particle surface has influence on the energy level splitting. The modifications are also predicted to be observable in realistic conditions where unavoidable size dispersion has to be taken into account. The emission spectrum results from the contribution of three distinct regions, a cluster core, a cluster shell and a very surface, the latter being almost completely quenched in realistic conditions. Eventually, by detailing the spectra of the ions embedded at different positions in the cluster we get an estimate of about 0.5 nm for the extent of the crystal field induced Stark effect. Due to the similarity between Y2O3 and Gd2O3, these results apply also to Eu3+ doped Y2O3 nanoparticles

Comparison of aluminum oxide empirical potentials from cluster to nanoparticle

Aluminum oxide nanoparticles are increasingly sought in numerous technological applications. However, as the nanoparticles grow during the synthesis, two phase transitions occur. At the nanoscale, numerical simulation of the stability of the alumina phases requires the use of empirical potentials that are reliable over a large range of system sizes going from a few atoms to several hundred thousand atoms. In this work, we confronted four different empirical potentials that are currently employed for bulk alumina. We found that only two of them are correct at the molecular level when compared to DFT calculations. Furthermore, the two potentials remain the best at the nanoscale as they reproduce one or two phase transitions that were observed experimentally: from amorphous solid to cubic crystal ({\gamma}) and from cubic to hexagonal ({\alpha}, i.e. corundum) crystal.Comment: 11 pages, 8 pdf figures, 1 supplemental material pdf file, accepted in Physical Review

Reducing Hygiene-Related Disease and Malnutrition in Rwanda

Water sanitation and hygiene-related disease and malnutrition are a high priority in developing countries, including Rwanda. Interventions that can trigger and sustain household-level behavioral change and practice are needed. A case-control study was conducted to assess the potential of the Community Health Club (CHC) intervention, which consisted of village-based health education on water sanitation, hygiene, nutrition, and monitoring of households’ practices to reduce water sanitation and hygiene-related disease and malnutrition. The study targeted one village which had been exposed to the CHC. As a control, one village was picked from among villages that had not been exposed to CHC intervention. The two villages were in the catchment area of the Nyabitimbo Health Center and shared the same water sources for domestic use in the Rusizi district in Rwanda. The study examined the prevalence of intestinal worms, diarrhea, and malnutrition among children under 5 years old as recorded in the registries of Nyabitimbo Health Center for the period of the study, 2013–2015. The study results revealed that the CHC intervention was associated with a reduction of intestinal worms, diarrhea, and malnutrition, but the results were only statistically significant for intestinal worms and malnutrition. The present study, being exploratory, can serve for planning and practice purposes at the specific study area

Insights from the Implementation and Adoption of Community-Based Health Interventions

Abstract Effective implementation of health interventions is critical for maximum adoption and optimal health outcomes. This qualitative study assessed the differences in Community Health Club (CHC) implementation in villages using qualitative research methods. Villages in Rusizi district in Rwanda were purposively selected with high, medium, and low adoption rates. The results revealed that the traits and skills of intervention facilitators (providers or implementers) at the village level, the involvement of the head of the village in the CHC intervention activities, and the support supervision by the Community Environmental Health Officer from the health center may have contributed to high rates of adoption of the intervention. Poor community organization, mistrust, lack of equal consideration among intervention beneficiaries, and lack of skills and capacity for intervention facilitators may have contributed to the low rates of intervention adoption. The results of this study suggest the need for capacity building of implementers, local leaders, and supervisors for improved (1) skills to adapt to local contexts and maximize the intervention adoption, (2) involvement and participation of local leadership, and (3) support supervision, guidance, and close monitoring, respectively. for effective implementation and maximum adoption of CHC intervention

Photoluminescence of Fully Inorganic Colloidal Gold Nanocluster and Their Manipulation Using Surface Charge Effects

International audienceFully inorganic, colloidal gold nanoclusters (NCs) constitute a new class of nanomaterials that are clearly distinguishable from their commonly studied metal–organic ligand-capped counterparts. As their synthesis by chemical methods is challenging, details about their optical properties remain widely unknown. In this work, laser fragmentation in liquids is performed to produce fully inorganic and size-controlled colloidal gold NCs with monomodal particle size distributions and an fcc-like structure. Results reveal that these NCs exhibit highly pronounced photoluminescence with quantum yields of 2%. The emission behavior of small (2–2.5 nm) and ultrasmall (<1 nm) NCs is significantly different and dominated by either core- or surface-based emission states. It is further verified that emission intensities are a function of the surface charge density, which is easily controllable by the pH of the surrounding medium. This experimentally observed correlation between surface charge and photoluminescence emission intensity is confirmed by density functional theoretical simulations, demonstrating that fully inorganic NCs provide an appropriate material to bridge the gap between experimental and computational studies of NCs. The presented study deepens the understanding of electronic structures in fully inorganic colloidal gold NCs and how to systematically tune their optical properties via surface charge density and particle size

Microsources photoniques à base de nanocristaux de silicium

L'étude intitulée "microsources photoniques à base de nanocristaux de silicium" porte sur l'utilisation du silicium comme matériau actif dans une source de lumière. On cherche donc à déterminer si le silicium, omniprésent dans l'industrie de l'électronique, peut également être utilisé dans l'optoélectronique. Notre but est alors de réaliser une source utilisant comme matériau émetteur des nanocristaux de silicium. Ce sont des grains de silicium monocristallins, sphériques et d'un diamètre compris entre 3 nm et 7.5 nm. Leur émission dans le visible est interprétée dans le cadre du confinement quantique. Les nanocristaux sont placés dans une cavité résonante formée par deux miroirs de Bragg. Les miroirs de Bragg sont composés de matériaux diélectriques: SiO2 et TiO2. La cavité plane ainsi constituée est le dispositif le plus couramment utilisé pour la réalisation de laser. Ce travail comporte quatre parties distinctes. La première partie concerne l'étude des propriétés intrinsèques des nanocristaux de silicium en couche mince: indices optiques et propriétés de photoluminescence. Dans une seconde partie, nous avons étudié les miroirs de Bragg et les cavités planes afin d'optimiser nos sources pour l'émission verticale. La troisième partie décrit la réalisation et la caractérisation en photoluminescence des sources. On a notamment observé la modification de l'émission spontanée induite par la cavité, à partir de mesures de temps de vie de photoluminescence. La réalisation et la caractérisation des cavités planes présentant une direction de confinement étant concluante, nous avons étudié les structures autorisants le confinement de la lumière selon 2 directions puis 3 directions. Dans la quatrième partie, nous exposons donc l'étude préliminaire traitant du confinement de la lumière au sein d'un dépôt de nanocristaux arrangé en cristal photonique 2D. Nous avons réalisé des dépôts structurés et nous avons calculé la structure de bande photonique correspondant à la morphologie idéal du cristal photonique 2D.The doctoral thesis entitled "silicon nanocrystals based photonic microsources" deals with the use of silicon as emitter material in light sources. We want to know if silicon, omnipresent in the electronic industry, may offer new oppor-tunity in the field of optoelectronic. The main aim consists in making silicon nanocrystals based cavities. The silicon monocrystalline grains, named sili-con nanocrystals, have spherical shapes with diameters between 3 nm and 7.5 nm. The nanocrystals strong photoluminescence in the visible range is ascribed to the effect of quantum confinement. The active layer composed of silicon nanocrystals is placed in a Fabry-Pérrot resonator. It is a plane cavity surrounded by two dielectric mirrors composed of silicon oxide and titanium oxide. This device correspond to laser device. Our work can be di-vided into four part. The first part is dedicated to the silicon nanocrystals thin film properties : optical index and photoluminescence properties. The second part is dedicated to the cavities properties and to the Bragg mirrors properties. This theoretical part allows to improve sources properties by well fitting cavities design. In the third part, we describe the production and the photoluminescence characterisation of half cavities and full cavities. Espe cially, we have deduced from the life time measurements, the spontaneous emission rate evolution induced by the cavity. Since the production and the characterisation of plane cavities were successful, we investigated 2D and 3D light confinement devices. In the fourth part, we report the preliminary study about light confinement in silicon nanocrystals based 2D photonic crystals. We have produced nanostructured films composed of silicon nanocrystals. We have theoretically investigated the photonic band structure of 2D structured films.LYON-Ecole Centrale (690812301) / SudocSudocFranceF

Ondes de choc générées par laser à une interface liquide solide

International audienceL’ablation d’une cible à une interface solide liquide génère des ondes de choc se propageant dans la cible, dans le liquide, mais également à l’interface solide-liquide. Les ondes de surface peuvent également se coupler au liquide, générant des fronts d’onde en forme de cônes de Mach dans le liquide. Nous avons développé un système d’imagerie par ombroscopie résolu en temps à l’échelle de la nanoseconde afin d’observer la propagation dans le liquide des différents fronts d’onde, en poursuivant deux objectifs : (i) la mesure de la pression générée au point d’ablation et (ii) la mesure des modules d’élasticité de la surface de l’échantillon. Concernant le premier objectif, nous exploitons le fait que l’onde hémisphérique générée par l’ablation de la cible est supersonique durant les cinquante premières nanosecondes. Ainsi, à partir de la conservation de la quantité de mouvement et de l’équation d’état déterminée par Rice et Walch, il est possible de remonter à la pression au point d’ablation [A. Chemin et al., Appl. Surf. Sci. 574, 151592, 2022]. Concernant le second objectif, l’observation de l’angle que forme les « cônes de Mach » avec la surface de l’échantillon permet de mesurer facilement la vitesse de propagation des ondes de surface, information traditionnellement compliqué à obtenir. Ainsi, nous pouvons mesurer la vitesse de l’onde de Rayleigh fuyante, ainsi que de l’onde longitudinal se propageant à l’interface. Ces deux mesures permettent de déduire le module d’Young ainsi que le coefficient de Poisson de la cible. Cette approche permet d’envisager l’élaboration d’un dispositif donnant simplement les modules d’élasticité de surface d’un échantillon [Demande de brevet n° 2105079]. Pour des échantillons homogènes, nos mesures ont été confirmées par des mesures acoustiques de type écho d’impulsion

Ondes de choc générées par laser à une interface liquide solide

International audienceL’ablation d’une cible à une interface solide liquide génère des ondes de choc se propageant dans la cible, dans le liquide, mais également à l’interface solide-liquide. Les ondes de surface peuvent également se coupler au liquide, générant des fronts d’onde en forme de cônes de Mach dans le liquide. Nous avons développé un système d’imagerie par ombroscopie résolu en temps à l’échelle de la nanoseconde afin d’observer la propagation dans le liquide des différents fronts d’onde, en poursuivant deux objectifs : (i) la mesure de la pression générée au point d’ablation et (ii) la mesure des modules d’élasticité de la surface de l’échantillon. Concernant le premier objectif, nous exploitons le fait que l’onde hémisphérique générée par l’ablation de la cible est supersonique durant les cinquante premières nanosecondes. Ainsi, à partir de la conservation de la quantité de mouvement et de l’équation d’état déterminée par Rice et Walch, il est possible de remonter à la pression au point d’ablation [A. Chemin et al., Appl. Surf. Sci. 574, 151592, 2022]. Concernant le second objectif, l’observation de l’angle que forme les « cônes de Mach » avec la surface de l’échantillon permet de mesurer facilement la vitesse de propagation des ondes de surface, information traditionnellement compliqué à obtenir. Ainsi, nous pouvons mesurer la vitesse de l’onde de Rayleigh fuyante, ainsi que de l’onde longitudinal se propageant à l’interface. Ces deux mesures permettent de déduire le module d’Young ainsi que le coefficient de Poisson de la cible. Cette approche permet d’envisager l’élaboration d’un dispositif donnant simplement les modules d’élasticité de surface d’un échantillon [Demande de brevet n° 2105079]. Pour des échantillons homogènes, nos mesures ont été confirmées par des mesures acoustiques de type écho d’impulsion