Within semiconductor quantum dots (QDs), exciton recombination processes are noteworthy for depending on the nature of surface coordination and nanocrystal/ligand bonding. The influence of the molecular surroundings on QDs optoelectronic properties is therefore intensively studied. Here, from the converse point of view, we analyse and model the influence of QDs optoelectronic properties on their ligands. As revealed by sum-frequency generation spectroscopy, the vibrational structure of ligands is critically correlated to QDs electronic structure when these are pumped into their excitonic states. Given the different hypotheses commonly put forward, such a correlation is expected to derive from either a direct overlap between the electronic wavefunctions, a charge transfer, or an energy transfer. Assuming that the polarizability of ligands is subordinate to the local electric field induced by excitons through dipolar interaction, our classical model based on nonlinear optics unambiguously supports the latter hypothesis.

We report on the recent scientific research contribution of non-linear optics based on Sum-Frequency Generation (SFG) spectroscopy as a surface probe of the plasmonic properties of materials. In this review, we present a general introduction to the fundamentals of SFG spectroscopy, a well-established optical surface probe used in various domains of physical chemistry, when applied to plasmonic materials. The interest of using SFG spectroscopy as a complementary tool to surface-enhanced Raman spectroscopy in order to probe the surface chemistry of metallic nanoparticles is illustrated by taking advantage of the optical amplification induced by the coupling to the localized surface plasmon resonance. A short review of the first developments of SFG applications in nanomaterials is presented to span the previous emergent literature on the subject. Afterwards, the emphasis is put on the recent developments and applications of the technique over the five last years in order to illustrate that SFG spectroscopy coupled to plasmonic nanomaterials is now mature enough to be considered a promising research field of non-linear plasmonics.

In this paper, we report on the study of a novel type of substrate based on a highly crystalline ZnO film photo-irradiated by UV for enhancing Raman signal. This effect...

Gold nanotriangles structured as honeycombs and fabricated by nanosphere lithography on a gold film are functionalized by thiophenol molecules in order to be used as plasmonic sensors in nonlinear optical sum-frequency generation (SFG) spectroscopy. The monitoring and the characterization of the surface optical properties are performed by UV-Visible differential reflectance spectroscopy showing an absorbance maximum located at 540 nm for p-and s-polarisation beams. SFG spectroscopy proves to be effective for thiophenol detection in ssp-polarisation scheme while the molecular SFG signal disappears in ppp-configuration due to the strong s-d interband contribution of gold. However, in ssp-configuration, the vibration modes of thiophenol molecules at 3050 and 3071 cm −1 are yet observed thanks to the excitation of a transversal plasmon mode by the incident visible laser beam, whereas they are usually very difficult to distinguish by Surface Enhanced Raman Scattering (SERS) and other vibrational optical probes.

We investigate the effects of the concentration of CdTe quantum dots (QDs) on their fluorescence in water. The emission spectra, acquired in right angle geometry, exhibit highly variable shapes. The measurements evidence a critical value of the concentration beyond which the intensity and the spectral bandwidth decrease and the fluorescence maximum is redshifted. To account for these observations, we develop a model based on the primary and secondary inner filter effects. The accuracy of the model ensures that the concentration dependent behaviour of QD fluorescence is completely due to inner filter effects. This result is all the more interesting because it precludes the assumption of dynamic quenching. As a matter of fact, the decrease of the emission intensity is not a consequence of collisional quenching but an effect of competition between fluorescence and absorption. We even show that this phenomenon is linked not only to the QD concentration but also to the geometric configuration of the setup. Hence, our analytical model can be easily adapted to every fluorescence spectroscopy configuration to quantitatively predict or correct inner filter effects in the case of QDs or any fluorophore, and thus improve the handling of fluorescence spectroscopy for highly concentrated solutions.

As luminescent quantum dots (QDs) are known to aggregate themselves through their chemical activation by carbodiimide chemistry and their functionalization with biotin molecules, we investigate both effects on the fluorescence properties of CdTe QDs and their impact on Förster Resonant Energy Transfer (FRET) occurring with fluorescent streptavidin molecules (FA). First, the QDs fluorescence spectrum undergoes significant changes during the activation step which are explained thanks to an original analytical model based on QDs intra-aggregate screening and inter-QDs FRET. We also highlight the strong influence of biotin in solution on FRET efficiency, and define the experimental conditions maximizing the FRET. Finally, a free-QD-based system and an aggregated-QD-based system are studied in order to compare their detection threshold. The results show a minimum concentration limit of 80 nM in FA for the former while it is equal to 5 nM for the latter, favouring monitored aggregation in the design of QDs-based biosensors.

The manufacturing of silica platforms functionalized by CdTe quantum dots (QDs) of 3.4 nm diameter through (3aminopropy)triethoxysilane (APTES) aliphatic organosilanes is performed to preserve QDs excitonic properties after their transfer from colloidal solutions to surfaces at ambient air. In these conditions, the chemical stability and the structural homogeneity of monolayers are monitored and attested by probing their optical efficiency through UV-Visible spectroscopy (absorption), time-resolved fluorescence spectroscopy and microscopy (emission). The grafting of the aliphatic organosilanes on silicon is examined by XPS measurements that show that a 0.9 nm sublayer thickness is electrostatically stabilized between SiO2 substrates and QDs layers without EDC-NHS (1-ethyl-3-(3-dimethyl-aminopropyl)carbodiimide, N-hydroxysuccinimide) activation. Surprisingly, in the latter case, the optical absorption of the QD layer does not vary beyond 10 days while it degrades in one day if QDs are activated. Finally, SFG spectroscopy evidences a vibroelectronic coupling between the QDs and APTES monolayers constituting the platforms.

We present a general formalism to model and calculate linear and nonlinear optical processes in composite systems, based on a graphical representation of light-matter interactions by loop diagrams associated to Feynman rules. Through this formalism, we recover the usual second-order response of a simple system by drawing four times less loop diagrams than doubled-sided ones. For composite systems, we introduce coupling hamiltonians between subsystems (for example a molecule and a substrate), graphically represented by virtual bosons. In this way, we enumerate all the diagrams describing the second-order response of the system and show how to select those relevant for the calculation of the molecular second-order hyperpolarizabilities under the influence of the substrate, including effective second-order contributions from the molecular third-order response. As it applies to all nonlinear processes and an arbitrary number of interacting partners, this representation provides a general frame for the calculation of the nonlinear response of arbitrarily complex systems.