On-demand reversible switching of the emission mode of individual semiconductor quantum emitters using plasmonic metasurfaces

The field of quantum technology has been rapidly expanding in the past decades, yielding numerous applications as quantum information, quantum communication and quantum cybersecurity. The central building block for these applications is a quantum emitter (QE), a controllable source of single photons or photon pairs. Semiconductor QEs such as perovskite nanocrystals (PNCs) and semiconductor quantum dots (QDs) have been demonstrated to be a promising material for pure single-photon emission, and their hybrids with plasmonic nanocavities may serve as sources of photon pairs. Here we have designed a system in which individual quantum emitters and their ensembles can be traced before, during, and after the interaction with the external plasmonic metasurface in controllable way. Upon coupling the external plasmonic metasurface to the array of QEs, the individual QEs switch from single-photon to photon-pair emission mode. Remarkably, this method does not affect the chemical structure and composition of the QEs, allowing them to return to their initial state after decoupling from the plasmonic metasurface. By employing this approach, we have successfully demonstrated the reversible switching of the ensemble of individual semiconductor QEs between single-photon and photon pair emission modes. This significantly broadens the potential applications of semiconductor QEs in quantum technologies

Surface ligands affect photoinduced modulation of the quantum dots optical performance

ABSTRACT Changes of optical properties of the solutions of CdSe/ZnS quantum dots (QDs) covered with the trioctylphosphine oxide (TOPO) ligands under the pulsed ultraviolet (UV) laser irradiation are observed. The fluorescence quantum yield (QY) of QDs decreases by more than an order of magnitude when the radiation dose approaches 2 × 10 -15 J per particle. This process is accompanied by a blue shift of both fluorescence and the first excitonic absorption peaks. The fluorescence quenching becomes less pronounced when the overall TOPO content in the solution is increased. When ТОРО ligands are replaced with n-hexadecylamine (HDA), QY and spectral properties are not changed at the same irradiation conditions. We assume that the above changes of the optical properties are associated with photooxidation of TOPO ligands by excited QD. Such process is less probable for the HDA ligand due to its different energy structure

Induced Transparency in Plasmon-Exciton Nanostructures for Sensing Applications

International audienceThe effect of induced transparency, which is related to photoinduced bleaching of photoabsorbers, is being intensely studied and has many applications in the field of sensing. Along with this classical effect, numerous studies on induced transparency in coupled plasmon–exciton systems, which is accompanied by the formation of hybrid states, have been recently published. The formation of a new coupled system results in various spectral modifications. For example, induced transparency manifests itself as a narrow dip in the absorption spectrum of a coupled system. This effect can be used in sensing, the feasibility of which is the main objective here, where a variety of materials and methods for obtaining the induced transparency are considered. Various morphologies and geometries of plasmonic nanoparticles are discussed as well as types of molecular absorbers to assess the most favorable combinations for the evolvement of induced transparency. The potential applications of the induced transparency effect in sensing and molecular diagnostics are summarized

Synergy of excitation enhancement and the purcell effect for strong photoluminescence enhancement in a thin-film hybrid structure based on quantum dots and plasmon nanoparticles

Reliable control of spontaneous radiation from quantum emitters, such as quantum dots (QDs), is an extremely important problem in quantum science, nanophotonics, and engineering. The QD photoluminescence (PL) may be enhanced near plasmon nanoparticles because of excitation field enhancement or the Purcell effect. However, both of these effects have their specific limitations. The excitation enhancement is usually accompanied by a decrease in the PL quantum yield (QY) due to the plasmon-induced energy transfer, and the Purcell effect cannot significantly enhance the PL of QDs with an initially high QY because of the obvious limitation of the QY by the value of 100%. Here, we have shown that the synergistic combination of excitation enhancement caused by silver nanospheres and the Purcell effect caused by silver nanoplates in the same QD-in-polymer hybrid thin-film nanostructure permits simultaneous increases in the radiative and excitation rates to be obtained. This overcomes the limitations of each individual effect and yields a synergistic PL increase (+1320%) greater than the sum of the PL enhancements determined by each effect alone (+70% and +360%).The financial support from the Ministry of Science and Higher Education of the Russian Federation through Grant No. 14.Y26.31.0011 is acknowledged. Y.R. acknowledges the support from the Basque Government (Grant No. IT1164-19). I.N. is grateful to the Université de Reims Champagne-Ardenne, the Ministry of Higher Education, Research and Innovation, and the Conseil Regional de Grand Est of France for support.Peer reviewe

Determination of the Single-Exciton Two-Photon Absorption Cross Sections of Semiconductor Nanocrystals through the Measurement of Saturation of Their Two-Photon-Excited Photoluminescence

International audienc

Enhanced spontaneous emission from two-photon-pumped quantum dots in a porous silicon microcavity

International audience(IN) Received XX Month XXXX; revised XX Month, XXXX; accepted XX Month XXXX; posted XX Month XXXX (Doc. ID XXXXX); published XX Month XXXX Photoluminescence (PL)-based sensing techniques have been significantly developed in practice due to their key advantages in terms of sensitivity and versatility of the approach. Recently, various nanostructured and hybrid materials have been used to improve the PL quantum yield and spectral resolution. The near-infrared (NIR) fluorescence excitation has attracted much attention because it offers deep tissue penetration and avoiding the autofluorescence of the biological samples. In our study, we have shown both spectral and temporal PL modifications under two-photon excitation of quantum dots (QDs) placed in one-dimensional porous silicon photonic crystal (PhC) microcavities. We have demonstrated an up to 4.3-fold Purcell enhancement of the radiative relaxation rate under two-photon excitation. The data show that the use of porous silicon PhC microcavities operating in the weak coupling regime permits the enhancement of the PL quantum yield of QDs under two-photon excitation, thus extending the limits of their biosensing applications in the NIR region of optical spectrum. © 2020 Optical Society of America Light-matter resonance interaction enables control over spontaneous photoluminescence (PL) emission properties of various luminophores, including organic dyes [1,2], rare-earth ions [3], 2D metal dichalcogenides [4], and fluorescent nanocrystals [5,6]. The so-called "weak" coupling regime makes it possible to change the spectral, spatial, and temporal properties of the luminophore PL emission by varying the local electromagnetic environment [7]. The use of photonic crystals (PhCs) is one of the most promising approaches to controlling the electromagnetic field distribution and, hence, to coupling it to the emitters placed inside the PhC microcavities (MCs) [1,3,4,7]. This approach is of special interest in the field of sensing in such emerging areas as the healthcare, environmental monitoring, and food safety [8,9]. Recent studies have demonstrated significant advances of PL-based sensors employing PhC structures in order to improve the critical properties of PL labels [9,10]. Porous silicon (pSi) MCs have been shown to be promising for biosensing applications due to the simplicity and scalability of fabrication and highly developed pore structure making the sensor surface easily accessible for analytes [11-13]. However, the necessity of selective excitation of majority of conventional dyes in the visible region of optical spectrum, low photostability, brightness, and background due to the autofluorescence of biological samples remain the obstacles to wider use of PL-based biosensor techniques. Excitation of the PL probes in the near-infrared (NIR) transparency window of biological samples could resolve some of these problems, allowing one deeper tissue penetration, higher spectral resolution and avoiding the autofluorescence. The nonlinear regime of two-photon excitation is a way to obtain visible-range fluorescence using NIR light sources. Moreover, the use of semiconductor quantum dots (QDs) with uniquely high two-photon absorption cross-sections compared to conventional dyes [14,15] allows one to reach the unprecedentedly high values of fluorescence contrast [16]. In addition, QDs are the excellent probes for sensing due to their wide one-and two-photon absorption [17,18] and narrow PL spectra, high quantum yield [19], and excellent photostability [20,21]. In this study, we have investigated the spontaneous PL emission of CdSe(core)/ZnS/CdS/ZnS(multishell) QDs placed inside a porous silicon MCs under two-photon excitation. We have measured the spectral and temporal characteristics of the spontaneous PL emission of QDs under two-photon pumping, as well as their dependence on the pump power. Significant enhancement of the QD PL at the wavelength corresponding to the MC eigenmode and its suppression within the photonic bandgap were observed. The change in the QD PL spectrum inside the porous silicon microcavity depended on the excitation energy density because the relaxation rates of the PL signal in the spectral regions where it was enhanced or suppressed were different. The increase in the emission rate corresponding to the weak coupling between the exciton transition of QDs and the eigenmode of the MC has been shown, and Purcell factor was determined to be about 4.3

Strongly coupled exciton–plasmon nanohybrids reveal extraordinary resistance to harsh environmental stressors: temperature, pH and irradiation

Hybridized plexcitonic states have unique properties which have been widely studied in recent decades in many research fields targeted at both fundamental science and innovative applications. However, to make these applications come true one needs to ensure the stabilization and preservation of electronic states and optical transitions in hybrid nanostructures, especially under the influence of external stressors, in regimes, that have not yet been comprehensively investigated. The present work shows that the nanohybrid system, composed of plasmonic nanoparticles and J-aggregates of organic molecules, displays outstanding resistance to harsh environmental stressors such as temperature, pH and strong light irradiation as well as demonstrates long-term stability and processability of the nanostructures both in weak and strong coupling regimes. These findings contribute to a deeper understanding of the physicochemical properties of plexcitonic nanoparticles and may find important implications for the development of potential applications in optoelectronics, optical imaging and chemo-bio-sensing and, in general, in the field of optical materials science.Authors acknowledge the financial support from the Ministry of Education and Science of the Russian Federation (grant no. 14.Y26.31.0011). Y. R. acknowledges the support from the Basque Government (grant no. IT1164-19). M. G. acknowledges support from the Basque Government (PIBA 2018-34), and Diputación Foral de Guipúzcoa (RED 2018, RED 2019). A. S. I. acknowledges the Maria de Maeztu Units of Excellence Programme – Grant No. MDM-2017-0720 Ministry of Science, Innovation and Universities.Peer reviewe

Effect of spectral overlap and separation distance on exciton and biexciton quantum yields and radiative and nonradiative recombination rates in quantum dots near plasmon nanoparticles

Efficient biexciton (BX) photoluminescence (PL) from quantum dots (QDs) paves the way to the generation of entangled photons and related applications. However, the quantum yield (QY) of BX PL is much lower than that for single excitons (EX) due to efficient Auger-like recombination. In the vicinity of plasmon nanoparticles, the recombination rates of EX and BX may be affected by the Purcell effect, fluorescence quenching, and the excitation rate enhancement. Here, the effect of the plasmon resonance spectral position on the EX and BX PL is experimentally studied in two cases: when the plasmon band overlaps with the excitation wavelength and when it coincides with the QDs PL band. In the first case, the EX and BX excitation efficiencies are significantly increased but the EX QY reduced. As a result, the BX-to-EX QY ratio is higher than 1 at plasmon–exciton systems separations shorter than 40 nm. In the second case, the radiative recombination rates are enhanced by several orders of magnitude, which led to an increase in BX QY over distances of up to 90 nm. Finally, these two effects are obtained in the same hybrid structure, with the resultant increase in both excitation efficiency and QY of BX PL.They also acknowledge the financial support from theMinistry of Science and Higher Education of the Russian Federation (Grant Number: 14.Y26.31.0011) . Y.R. acknowledges the support from the Basque Government (IT1164‐19

Enhanced spontaneous emission from two-photon-pumped quantum dots in a porous silicon microcavity

Photoluminescence (PL)-based sensing techniques have been significantly developed in practice due to their key advantages in terms of sensitivity and versatility of the approach. Recently, various nanostructured and hybrid materials have been used to improve the PL quantum yield and the spectral resolution. The near-infrared (NIR) fluorescence excitation has attracted much attention because it offers deep tissue penetration and it avoids the autofluorescence of the biological samples. In our study, we have shown both spectral and temporal PL modifications under two-photon excitation of quantum dots (QDs) placed in one-dimensional porous silicon photonic crystal (PhC) microcavities. We have demonstrated an up-to-4.3-fold Purcell enhancement of the radiative relaxation rate under two-photon excitation. The data show that the use of porous silicon PhC microcavities operating in the weak coupling regime permits the enhancement of the PL quantum yield of QDs under two-photon excitation, thus extending the limits of their biosensing applications in the NIR region of the optical spectrum

Strong increase in the effective two-photon absorption cross-section of excitons in quantum dots due to the nonlinear interaction with localized plasmons in gold nanorods

International audienceExcitons 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: to increase their photoluminescence quantum yield (PL QY) or further increase the TPACS. Plasmonic nanoparticles (PNPs) may act as open nanocavities for increasing the PL QY via the Purcell effect, but this enhancement is strictly limited by the maximum possible QY 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 to use them in biosensing and nonlinear optoelectronics