Fermi level shift in carbon nanotubes by dye confinement

International audienceDye confinement into carbon nanotube significantly affects the electronic charge density distribution of the final hybrid system. Using the electron-phonon coupling sensitivity of the Raman G-band, we quantify experimentally how charge transfer from thiophene oligomers to single walled carbon nanotube is modulated by the diameter of the nano-container and its metallic or semiconducting character. This charge transfer is shown to restore the electron-phonon coupling into defected metallic nanotubes. For sub-nanometer diameter tube, an electron transfer optically activated is observed when the excitation energy matches the HOMO-LUMO transition of the confined oligothiophene. This electron doping accounts for an important enhancement of the photoluminescence intensity up to a factor of nearly six for optimal confinement configuration. This electron transfer shifts the Fermi level, acting on the photoluminescence efficiency. Therefore, thiophene oligomer encapsulation allows modulating the electronic structure and then the optical properties of the hybrid system

Photostability of Core-Shell Structures at Low Temperature

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Synthesis and Optical Properties of Graphene Quantum Dots

International audienceThe outstanding electronic, optical and mechanical properties of graphene strongly inspire the scientific community at both the fundamental and applicative levels. However, the key issue that needs to be addressed is the control and the modification of the electronic properties of graphene, and notably the opening of a sizable bandgap. For the last decade, a great attention has been paid to the size reduction of graphene using conventional top-down approaches (lithography and etching, thermal treatments and oxidation of bulk materials) to fabricate graphene quantum dots (GQDs) or graphene nanoribbons (GNRs). However, top-down approaches do not permit to manipulate the structure of the material at the atomic scale. In particular, they do not allow a sufficient control of the morphology and oxidation state of the edges, which drastically impact the properties. In order to truly control, with the required level of precision, the morphology and the composition of the materials and of its edges, the bottom-up approach is the relevant way to proceed. Recently, we reported on the synthesis and single photon emission properties of triangular-shaped GQDs. While, this initial report focused on functionalized nanoparticles, we now turn to non-functionalized graphene quantum dots that are in terms of structure closer to real graphene. Here, we described the synthesis, the dispersion and optical properties of a series of rod-shaped particles and we studied the structure-properties relationship in these graphene quantum dots. To this end, we designed a series of GQDs with a given edge type and by changing only one parameter (one dimension, namely the length or the width-Figure 1), we expect to follow simply the evolution of the optical properties

Synthesis and single-photon emission properties of graphene quantum dots

International audienceThe outstanding electronic, optical and mechanical properties of graphene strongly inspire the scientific community at both the fundamental and applicative levels. However, along this way several key scientific issues have to be addressed and one of the main challenges of the field is the control and modification of graphene electronic properties, and notably the controlled opening of a sizable bandgap. For the last decade, a great attention has been paid to the size reduction of graphene using conventional top-down approaches (lithography and etching, thermal treatments and oxidation of bulk materials) to fabricate graphene quantum dots (GQDs) or graphene nanoribbons (GNRs). However, top-down approaches do not permit to manipulate the structure of the material at the atomic scale. In particular, they do not allow a sufficient control of the morphology and oxidation state of the edges, which drastically impact the properties. In order to truly control, with the required level of precision, the morphology and the composition of the materials and of its edges, the bottom-up approach is the relevant way to proceed. With the aim to study and understand the optical properties of GQD materials, we performed the bottom-up synthesis of different families of nanoparticles exhibiting controlled shapes and edges. Using absorption, steady-state and time-resolved photoluminescence and photoluminescence excitation (PLE) spectroscopy, we try to establish the intrinsic optical properties of the GQDs and understand how the structure influences the properties. Here we present the synthesis of a new series of rod-shaped graphene nanoparticles (GNRods); we also present the single photon emission properties of a triangle-shaped GQ

Single photon emission from graphene quantum dots at room temperature

In the field of condensed matter, graphene plays a central role as an emerging material for nanoelectronics. Nevertheless, graphene is a semimetal, which constitutes a severe limitation for some future applications. Therefore, a lot of efforts are being made to develop semiconductor materials whose structure is compatible with the graphene lattice. In this perspective, little pieces of graphene represent a promising alternative. In particular, their electronic, optical and spin properties can be in principle controlled by designing their size, shape and edges. As an example, graphene nanoribbons with zigzag edges have localized spin polarized states. Likewise, singlet-triplet energy splitting can be chosen by designing the structure of graphene quantum dots. Moreover, bottom-up molecular synthesis put these potentialities at our fingertips. Here, we report on a single emitter study that directly addresses the intrinsic properties of a single graphene quantum dot. In particular, we show that graphene quantum dots emit single photons at room temperature with a high purity, a high brightness and a good photostability. These results pave the way to the development of new quantum systems based on these nanoscale pieces of graphen