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Excitons in semiconductor quantum dots (QDs) feature high values of the two-photon absorption cross-sections (TPACSs), enabling applications of two-photon-excited photoluminescence (TPE PL) of QDs in biosensing and nonlinear optoelectronics. However, efficient TPE PL of QDs requires high-intensity laser fields, which limits these applications. There are two possible ways to increase the TPE PL of QDs: by increasing their photoluminescence quantum yield (PLQY) or by further increasing the TPACS. Plasmonic nanoparticles (PNPs) may act as open nanocavities for increasing the PLQY via the Purcell effect, but this enhancement is strictly limited by the maximum possible PLQY value of 100%. Here we directly investigated the effect of PNPs on the effective TPACS of excitons in QDs. We have found that effective TPACS of excitons in a QD–PMMA thin film can be increased by a factor of up to 12 near the linearly excited gold nanorods (GNRs). Using gold nanospheres (GNSs), in which plasmons cannot be excited in the infrared range, as a control system, we have shown that, although both GNSs and GNRs increase the recombination rate of excitons, the TPACS is increased only in the case of GNRs. We believe that the observed effect of TPACS enhancement is a result of the nonlinear interaction of the plasmons in GNRs with excitons in QDs, which we have supported by numerical simulations. The results show the way to the rational design of the spectral features of plasmon–exciton hybrids for using them in biosensing and nonlinear optoelectronics., V. K. acknowledges support from the Russian Science Foundation (Grant No. 18-72-10143) for the part of the study related to the investigation of the effects of PNPs on the effective TPACS of excitons in QDs and numerical simulations of these effects. Support from the Ministry of Education and Science of the Russian Federation (Grant No. 14.Y26.31.0011) for the part of this study related to the synthesis and functionalisation of the QDs and engineering of hybrid QD-GNR materials is also acknowledged. Y. R. acknowledges the support from the Basque Government (grant no. IT1164-19). Y. R. and M. G. acknowledge the support from the Spanish MINECO (PID2019-111772RB-I00). I. N. acknowledges the Ministry of Higher Education, Research and Innovation of the French Republic and Université de Reims Champagne-Ardenne.

Enhancement of the photoluminescence signal intensity from organic and inorganic fluorophores increases the sensitivity of operation of optical sensors, detectors, and photonic diagnostic assays. Here, we have engineered and compared optical and fluorescence-enhancing properties of two types of one-dimensional porous silicon photonic crystals: a transfer-printed microcavity based on the freestanding photonic crystal and a conventional “one-piece” microcavity created on a monocrystalline silicon substrate. Comparative analysis of the eigenmodes and the photonic bandgaps of both types of microcavities demonstrated a high quality of transfer-printed microcavities and good correlation of their reflection spectra with the spectra of “one-piece” microcavities. Moreover, embedding of a highly concentrated solution of quantum dots (QDs) in the eigenmode localization region of transfer-printed microcavity was followed by three-fold reduction of the full-width-at-half-maximum of their luminescence spectrum at the microcavity eigenmode wavelength, thus confirming a weak coupling regime of QD exciton and microcavity eigenmode interaction and significant enhancement of QD luminescence within the microcavity.

Today, lots of research address the phenomenon of interaction between light and matter. In particular, it is of a special interest to investigate light–matter interaction in one-dimensional resonators based on porous materials. In this case, one can embed emitting semiconductor particles into the porous resonator, where the excitons of these particles couple to the resonator eigenmode and luminescence intensity of the emitters is enhanced, allowing an increase in the sensitivity of optical sensors, detectors, and photonic diagnostic assays. A particular challenge is to place the emitters directly in the antinode region of the resonator eigenmode in order to maximize the coupling strength, which is sometimes a problem due to the spatial distribution of emitters away from the eigenmode localization region. Here, we have shown that the transfer-printing technique can be used to obtain structures based on freestanding porous silicon photonic crystals capable of precisely controlling the emitter spatial distribution about the eigenmode localization region. This, as well as the porosity of these structures and high adsorption capacity of porous silicon, allows the light–matter interaction in these hybrid structures to be used in sensing applications. We have shown that the transfer-printing method does not worsen the optical properties of the microcavities compared to the conventional electrochemical etching of the whole microcavity at a time. Furthermore, we have observed slightly better coupling of the exciton of the emitter to the eigenmode of the transfer-printed microcavity in the weak coupling regime.

Semiconductor quantum dots (QDs) are known for their ability to exhibit multiphoton emission caused by recombination of biexcitons (BX). However, the quantum yield (QY) of BX emission is low due to the fast Auger process. Plasmonic nanoparticles (PNPs) provide an attractive opportunity to accelerate BX radiative recombination. Here, we demonstrate the PNPs induced distance-controlled enhancement of BX emission of single QDs. Studying the same single QD before and after its integration with the PNPs, we observed a plasmon-mediated increase in the QY of BX emission. Remarkably, the enhancement of BX emission remains pronounced even at distances of 170 nm. We attribute this effect to efficient coupling, which results in the trade-off between resonance energy transfer from QD to gold nanorods and the Purcell effect at small QD-PNP separations and the predominant influence of the Purcell effect at longer distances. Our findings constitute a reliable approach to managing the efficiency of multiexciton emission over a wide span of distances, thus paving the way for new applications., The authors acknowledge the financial support from the Ministry of Education and Science of the Russian Federation (Grant 14.Y26.31.0011). Y.R. acknowledges support from MINECO (Ministerio de Economiá y Competitividad, Spain), Project Fis2016.80174-P (PLASMOQUANTA).

Light-matter coupling between the molecular dipole transitions and a confined electromagnetic field provides the ability to control the fundamental properties of coupled matter. The use of tunable optical microcavities for electromagnetic field confinement allows one to affect the coupled state properties in a controllable manner, whereas the coupling strength in this system strongly depends on the transition dipole moment and a mode volume of the cavity. In this study we have demonstrated controllable emission of Rhodamine 6G organic molecules with relatively low and unoriented dipole moments in a strong coupling regime by placing them into a tunable Fabry-Perot microcavity.

Semiconductor quantum dots (QDs) are known for their unique photophysical properties and, in particular, their ability to multiphoton emission caused by recombination of biexcitons. However, the luminescence quantum yield of biexciton states is relatively low due to the fast Auger non-radiative process. Plasmonic nanoparticles can significantly accelerate the radiative rate of QDs. In this study we demonstrate the distance-controlled enhancement of the biexciton emission of single CdSe/ZnS/CdS/ZnS QDs due to their coupling with gold nanorods. We explain this enhancement as the distancedependent trade-off between the energy transfer and the Purcell effect. Our findings constitute a reliable approach to managing the efficiency of multiphoton emission over a wide span of distances.

Semiconductor quantum dots (QDs) have been demonstrated to be a promising material for developing innovative optoelectronic systems and lasers. The strong and weak coupling effects between localized plasmons in noble metal nanoparticles and excitons in QDs can modulate photoluminescence properties of the latter, scaling up their applications. In particular, these effects can strongly affect the photoluminescence (PL) lifetime of QDs, opening prospects for significantly increasing the quantum yield of the biexciton emission in single QD. Here, we provide а convincing proof of the formation of many-exciton states in hybrid material based on CdSe/ZnS/CdS/ZnS core/multishell QDs and gold nanorods (NRs) embedded in thin films of PMMA. The presence of NRs causes at least an order-of-magnitude decrease in the PL lifetimes of single QD. The obtained results have demonstrated the possibility of detecting biexciton states in QDs as the main component of emission of the hybrid QD-NR material., We acknowledge the support of grant no. 14.Y26.31.0011 of the Ministry of Education and Science of the Russian Federation. Y.R. acknowledges support from project Fis2016.80174-P (PLAS-MOQUANTA) from MINECO (Ministerio de Economiá y Competitividad), Spain.

International audience; The potential impact of nanoscience on energy transfer processes in biomolecules was investigated on the example of a complex between fluorescent semiconductor nanocrystals and photochromic membrane protein. The interactions between colloidal CdTe quantum dots (QDs) and bacteriorhodopsin (bR) protein were studied by a variety of spectroscopic techniques, including integrated and time-resolved fluorescence spectroscopies, zeta potential and size measurement, and fluorescence correlation spectroscopy. QDs’ luminescence was found to be strongly modulated by bacteriorhodopsin, but in a controllable way. Decreasing emission lifetimes and blue shifts in QDs’ emission at increasing protein concentrations suggest that quenching occurs via Förster resonance energy transfer. On the other hand, concave Stern-Volmer plots and sigmoidal photoluminescence quenching curves imply that the self-assembling of NCs and bR exists, and the number of nanocrystals (NCs) per bacteriorhodopsin contributing to energy transfer can be determined from the inflection points of sigmoidal curves. This number was found to be highly dependent not only on the spectral overlap between NC emission and bR absorption bands, but also on nanocrystal surface charge. These results demonstrate the potential of how inorganic nanoscale materials can be employed to improve the generic molecular functions of biomolecules. The observed interactions between CdTe nanocrystals and bacteriorhodopsin can provide the basis for the development of novel functional materials with unique photonic properties and applications in areas such as all-optical switching, photovoltaics and data storage.