Comparison of the photoluminescence properties of semiconductor quantum dots and non-blinking diamond nanoparticles. Observation of the diffusion of diamond nanoparticles in living cells

Long-term observations of photoluminescence at the single-molecule level were until recently very diffcult, due to the photobleaching of organic ?uorophore molecules. Although inorganic semiconductor nanocrystals can overcome this diffculty showing very low photobleaching yield, they suffer from photoblinking. A new marker has been recently introduced, relying on diamond nanoparticles containing photoluminescent color centers. In this work we compare the photoluminescence of single quantum dots (QDs) to the one of nanodiamonds containing a single-color center. Contrary to other markers, photoluminescent nanodiamonds present a perfect photostability and no photoblinking. At saturation of their excitation, nanodiamonds photoluminescence intensity is only three times smaller than the one of QDs. Moreover, the bright and stable photoluminescence of nanodiamonds allows wide field observations of single nanoparticles motion. We demonstrate the possibility of recording the tra jectory of such single particle in culture cells

Quantum efficiency of energy transfer in noncovalent carbon nanotube/porphyrin compounds

International audienceWe report on the quantum yield of excitation energy transfer in non-covalently bound nan- otube/porphyrin compounds. Evidence for energy transfer is gained from photoluminescence exci- tation experiments. We perform a quantitative evaluation of the transfer quantum yield in the case of (6,5) nanotubes through three independent methods : quantitative PLE measurements, evalu- ation of the luminescence quenching of the donor (porphyrin) and ultrafast transient absorption measurements. The latter shows a tremendous increase of the porphyrin recovery rate upon incor- poration in the compound. All these measurements consistently lead to an exceptional quantum yield efficiency

Pi-stacking functionalization through micelles swelling: Application to the synthesis of single wall carbon nanotube/porphyrin complexes for energy transfer

We report on a new, orginal and efficient method for "pi-stacking" functionalization of single wall carbon nanotubes. This method is applied to the synthesis of a high-yield light-harvesting system combining single wall carbon nanotubes and porphyrin molecules. We developed a micelle swelling technique that leads to controlled and stable complexes presenting an efficient energy transfer. We demonstrate the key role of the organic solvent in the functionalization mechanism. By swelling the micelles, the solvent helps the non water soluble porphyrins to reach the micelle core and allows a strong enhancement of the interaction between porphyrins and nanotubes. This technique opens new avenues for the functionalization of carbon nanostructures.Comment: 6 pages, 5 figure

Etude par microscopie en champ proche des phénomènes de migration de matière photo-induite dans les matériaux photochromiques

L'objectif de ce travail est d'étudier les phénomènes de déformation photo-induite de matière dans les films minces polymères incorporant des molécules d'azobenzène. Cette étude s'appuie sur une expérience originale qui consiste à observer in-situ la cinétique de formation d'un réseau de surface sous illumination du film photochromique par une figure d'interférence. L'observation est basée sur l'utilisation de techniques couplées de microscopie à sonde locale qui permettent de corréler la morphologie photo-induite et la distribution du champ électromagnétique avec une résolution très inférieure au pas du réseau. Cette étude, menée en fonction de la polarisation de la lumière et de l'épaisseur des films, démontre qu'au moins quatre mécanismes microscopiques interviennent dans la déformation photo-induite des azo-polymères : la réorientation optique des photochromes, la réorganisation locale de la matrice, le transport dirigé de matière, le photo-blanchiment. La contribution de ces différents mécanismes est plus particulièrement révélée par l'existence de deux phénomènes observés pour la première fois. D'une part, la cinétique de déformation présente une transition entre deux régimes, l'un, au temps court, en phase avec l'excitation lumineuse et l'autre, au temps long, en opposition de phase. D'autre part, la morphologie des réseaux photo-induits dépend de façon spectaculaire de l'épaisseur des couches. L'ensemble des résultats obtenus apporte un nouvel éclairage sur certaines observations expérimentales antérieures, parfois contradictoires, notamment sur la différence entre les réponses d'un même matériau à une excitation optique en champ proche et champ lointain.The main goal of this PhD work is to study photo-induced matter deformation phenomena in thin polymeric film containing azobenzene moieties. This study is based on the in-situ observation of surface relief gratings kinetic of formation under illumination by an interference pattern. The observation relies on a coupled microscopy technique, allowing to correlate photo-induced morphology with the electromagnetic field distribution, with a resolution better than the lattice pitch. The study as a function of the light polarisation and of the film thickness shows that four microscopic mechanisms are involved in the photo-induced deformation of the azo-polymer: the optical reorientation of chromophore, the local reorganization of the matrix, oriented matter transport and the photobleaching.The contribution of these different mechanisms is evidenced by two phenomena observed for the first time. First, the kinetic of deformation presents a transition between two regimes, one, at short time, in phase with the light excitation, the other, at longer time, in opposition of phase. Second, the morphology of the induced relief grating depends strongly on the film thickness. This PhD work shed light on previous and somehow contradictory results, in particular in term of response of azo-polymer films at an excitation in near filed and far field optics.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Photoluminescence Tuning Through Irradiation Defects in CH3_3NH3_3PbI3_3 Perovskites

International audienceDefect engineering is applied to hybrid (CH3NH3)PbI3 organic–inorganic perovskites. These materials have become one of the most promising low‐cost alternatives to traditional semiconductors in the field of photovoltaics and light emitting devices. Here Helium ion irradiation at low energy has been used as a tool for the controlled introduction of point defects in both single crystals and polycrystalline thin films. The irradiation defects modify the opto‐electronic properties as probed using photoluminescence (PL) spectroscopy from 10 K to room‐temperature. Contrary to usual semiconductors, a very good resilience of the PL properties with irradiation is observed, even associated to an enhancement of the optical emission at low temperature. These results are discussed in relation with the tetragonal to orthorhombic low‐temperature phase transition below T = 160 K. A comparison between spectra from single crystals and polycrystalline films, both with and without irradiation defects, allows a better understanding of the light emission mechanisms in both kinds of samples. The authors thereby evidence radiation hardness of these materials and the specificity of defects and their impact on light emission properties

Fast growth of monocrystalline thin films of 2D layered hybrid perovskite

International audienceDuring the past few years hybrid organic-inorganic perovskites (HOIPs) have attracted much interest as solution-processed semiconductors with high potentialities in optoelectronics and photovoltaics. On the one hand 3D HOIPs such as CH3NH3PbI3 have shown their outstanding performances when incorporated in solar cells [1]. On the other hand their 2D layered counterparts such as (C6H5C2H4NH3)2PbI4 (PEPI) are promising materials for light emitting devices because of their strong emission at room temperature [2]. However, the optoelectronic properties of hybrid perovskite polycrystalline films suffer from a microscale grain structure. In order to take advantage of the great potential of these materials for both photovoltaics and emitting devices, the synthesis of large monocrystalline films is a key issue. Here we propose a fast crystallization method for the 2D layered hybrid perovskite PEPI. A vapor-assisted process coupled with a capping of the precursor solution allows to grow 2-dimensionnal thin films with millimetric monocrystalline grains, a high aspect ratio and a good surface quality (Fig.1). Moreover, this growth is several orders of magnitudes faster than the other reported techniques. In addition, we highlight the benefits of using γ-butyrolactone (GBL) for the growth of layered perovskites monocrystalline grains

Excitonic properties and ultrafast carrier dynamics in hybrid organic-perovskites

International audienceDue to their high potentiality for photovoltaic applications or coherent light sources, a renewed interest in hybrid organic perovskites (HOPs) has emerged since 2012. HOPs can be arranged in such a way that carriers are free to move at 3D or at 2D. At 3D, the exciton binding energy has been shown to be of the order of tenth of meV. When they are arranged in two dimensions, these materials can be considered as hybrid multi-quantum wells. Both quantum and dielectric confinement lead to a huge exciton binding energy of several hundreds of meV.In this talk, we will first discuss about the excitonic properties of CH3NH3PbI3 single crystals at low temperature, and compare them to those of thin polycrystalline films. The main feature is the appearance of a sharp emission line (FWHM ~ 5 meV) at high energy that is tentatively attributed to the free exciton signature. Experiments as a function of temperature confirm the existence of a strong electron-phonon coupling in HOPs.Secondly, we will report on ultrafast pump-probe experiments performed on (C6H5C2H4NH3)2PbI4 thin layers at room temperature. The exciton dynamics is fitted with a bi-exponential decay with a free exciton life-time of ∼100 ps. The presence of a long tail in the pump/probe signal is attributed to trapped excitons on dark states, while an ultrafast intraband relaxation (τintra ≤ 150 fs) is reported. The analysis of the transient broadening and loss of oscillator strength demonstrates that 2D-HOPs share common behaviours with standard semiconductors quantum wells despite their huge exciton binding energy that is closer to the one reported for organic semiconductors. Finally, preliminary results on the intraband relaxation in CH3NH3PbI3 will be presented

Fast growth of monocrystalline thin films of 2D layered hybrid perovskite

International audienceHybrid organic-inorganic perovskites are on the way to deeply transform the photovoltaic domain. Likewise, it recently appears that this class of materials have a lot of assets for other optoelectronic applications. One key aspect is to be able to synthesize large areas of monocrystalline thin films. Here, we report on the development of a new synthesis method of 2D hybrid organic-inorganic perovskite called "Anti-solvent Vapor-assisted Capping Crystalliza-tion". This method allows to grow monocrystalline thin films with high aspect ratio in less than 30 minutes

Comparison of the photoluminescence properties of semiconductor quantum dots and non-blinking diamond nanoparticles. Observation of the diffusion of diamond nanoparticles in living cells.

International audienceLong-term observations of photoluminescence at the single-molecule level were until recently very diffcult, due to the photobleaching of organic fluorophore molecules. Although inorganic semiconductor nanocrystals can overcome this diffculty showing very low photobleaching yield, they suffer from photoblinking. A new marker has been recently introduced, relying on diamond nanoparticles containing photoluminescent color centers. In this work we compare the photoluminescence of single quantum dots (QDs) to the one of nanodiamonds containing a single-color center. Contrary to other markers, photoluminescent nanodiamonds present a perfect photostability and no photoblinking. At saturation of their excitation, nanodiamonds photoluminescence intensity is only three times smaller than the one of QDs. Moreover, the bright and stable photoluminescence of nanodiamonds allows wide field observations of single nanoparticles motion. We demonstrate the possibility of recording the tra jectory of such single particle in culture cells