Long path DOAS measurements of atmospheric pollutants concentration

A differential optical absorption spectroscopy gas-analyzer consisted of a coaxial telescope, a spectrometer, an analyzer and retroreflector was successfully tested. A high pressure 150-W Xe arc lamp was employed as a light source. In order to record the spectra, a monochrometer with a grating and photodiode array was used. Gas analyzer spectral data bank includes more than 35 moleculas absorbed in UV spectral region. The measured absorption spectra were evaluated by using a least-squares fit to determine the average mixing ratio of each species in the atmosphere. As a result of experiments time series of concentrations of gases polluting the atmosphere were trace measured. Minimally detected concentration on pathlength 480 m is the unit of ppb at the time of accumulation of 2 min. The results of the field test measurements of pollutants in Tomsk city are presented

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

Long path DOAS measurements of atmospheric pollutants concentration

A differential optical absorption spectroscopy gas-analyzer consisted of a coaxial telescope, a spectrometer, an analyzer and retroreflector was successfully tested. A high pressure 150-W Xe arc lamp was employed as a light source. In order to record the spectra, a monochrometer with a grating and photodiode array was used. Gas analyzer spectral data bank includes more than 35 moleculas absorbed in UV spectral region. The measured absorption spectra were evaluated by using a least-squares fit to determine the average mixing ratio of each species in the atmosphere. As a result of experiments time series of concentrations of gases polluting the atmosphere were trace measured. Minimally detected concentration on pathlength 480 m is the unit of ppb at the time of accumulation of 2 min. The results of the field test measurements of pollutants in Tomsk city are presented

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

Energy transfer between single semiconductor quantum dots and organic dye molecules

An understanding of the mechanisms of energy transfer and conversion on the nanoscale is one of the key requirements for an implementation of highly efficient photonic nanodevices based on hybrid organic/inorganic nanomaterials. In this work we conduct steady-state and time resolved optical studies of the emission properties of an ensembles and single semiconductor quantum dots and attached organic dye molecules. We revealed that the luminescence intensity of a hybrid structure does not follow the blinking behavior of quantum dots. We also demonstrated an efficient single photon generation from single hybrid nanostructures which involves an energy transfer from donor to acceptor as main excitation source.This work was supported by the Ministry of Education and Science of the Russian Federation under grant no. 14.Y26.31.0011. Y. R. and T. H. acknowledges support from Project Fis2016.80174-P (PLASMOQUANTA) from MINECO (Ministerio de Economiá y Competitividad), Spain.Peer reviewe

Plasmon–exciton interaction strongly increases the efficiency of a quantum dot-based near-infrared photodetector operating in the two-photon absorption mode under normal conditions

Semiconductor quantum dots (QDs) are known for their high two-photon absorption (TPA) capacity. This allows them to efficiently absorb infrared photons with energies lower than the bandgap energy. Moreover, TPA in QDs can be further enhanced by the interaction of excitons of the QDs with plasmons of a metal nanoparticle. We fabricated nonlinear plasmon–exciton photodetectors based on QDs and silver nanoplates (SNPs) to demonstrate the optoelectronic application of these effects. A thin layer of CdSe QDs was used as a source of charge carriers for a photoresistor-type photodetector. SNPs with near-infrared plasmon modes were introduced into the layer of QDs to increase the light absorption efficiency. Under near-infrared irradiation, the power of the dependence of the photocurrent on the excitation intensity was twice the power of the corresponding dependence under one-photon excitation with visible light. This proved that the new photodetector efficiently operated under two-photon excitation. Although the SNP light absorption was linear, energy was transferred from plasmons to excitons in the two-quantum mode, which led to a nonlinear dependence. Moreover, we found that the photocurrent from the designed photodetector containing the QD–SNP composite was an order of magnitude higher than that from a photodetector containing QDs alone. This can be explained by the plasmon-induced increase in the TPA efficiency.This study was supported by the Russian Science Foundation, grant no. 18-72-10143. The part of this study dealing with the synthesis and characterization of nanomaterials was supported by the Russian Science Foundation, grant no. 18-19-00588. V. K. has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie, grant agreement no. 101025664 (QESPEM). I. N. acknowledges support of the French National Research Agency (ANR-20-CE19-009-02) and co-funding by the European Union via the European Regional Development Fund (FreeBioWave project).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

Enhancement of biexciton emission due to long-range interaction of single quantum dots and gold nanorods in a thin-film hybrid nanostructure

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)