Strong exciton-photon coupling with colloidal quantum dots in a tuneable microcavity

Polariton emission from optical cavities integrated with various luminophores has been extensively studied recently due to the wide variety of possible applications in photonics, particularly promising in terms of fabrication of low-threshold sources of coherent emission. Tuneable microcavities allow extensive investigation of the photophysical properties of matter placed inside the cavity by deterministically changing the coupling strength and controllable switching from weak to strong and ultra-strong coupling regimes. Here we demonstrate room temperature strong coupling of exciton transitions in CdSe/ZnS/CdS/ZnS colloidal quantum dots with the optical modes of a tuneable low-mode-volume microcavity. Strong coupling is evidenced by a large Rabi splitting of the photoluminescence spectra depending on the detuning of the microcavity. A coupling strength of 154 meV has been achieved. High quantum yields, excellent photostability, and scalability of fabrication of QDs paves the way to practical applications of coupled systems based on colloidal QDs in photonics, optoelectronics, and sensing.Comment: 14 pages, 3 figure

Liberation of the signified from a rigid connection with the signifier as one of the conditions of the arbitrary nature of the sign

How do arbitrary signs occur? The article suggests that the basis of arbitrariness is the liberation of the signified from a rigid connection with the signifier. An important role is played by the psychological present. The psychological present is not one-dimensional but is represented by dimensions of sequence, simultaneity, and duration. Non-arbitrary signs are as if one-dimensional: the signifier and the signified are in undifferentiated unity – in one dimension of the present time. When forming arbitrary signs, the signified and the signifier are separated from each other and are embodied in different dimensions – the levels of the psychological present tense, invariant and variable. At the same time, the signified occupies an invariant level, and the signifier is variable so that the signified remains constant with any change in the signifier. Therefore, different signifiers can be applied to the same object at will, and the content of the designated object does not change. The signified thus becomes relatively independent and free from the signifier

ОБ ОСОБЕННОСТЯХ ЗНАКОВОЙ СИСТЕМЫ ИНСТРУМЕНТАЛЬНОГО УСЛОВНОГО РЕФЛЕКСА

The purpose of this article is to identify the characteristics of instrumental conditioned reflex as a sign system. In conditioned reflex the sign is a conditioned stimulus. It contains unconditioned stimulus in «idealized» form and causes reflex activities. In classical conditioning a sign directly leads to the reinforcement. However, the results of classical conditioning caused by limited responses that are similar to the unconditioned reflex. So often the sign in a classical conditioned reflex is not able to lead to the reinforcement. In this case, the reinforcement is only possible due to the emergence of animal motor activity. It is the formation of instrumental conditioned reflex. Instrumental reactions complicate and mediate the relationship between the sign and the unconditioned stimulus. By means of the «idealization» of unconditioned stimulus signs are not only new different stimuli both in classical conditioning but also motivate new activities that go beyond the innate unconditioned reflex reactions. The emergence of instrumental activity abolishes unconditioned reflex effects and generates useful results as a positive reinforcement. In this case, the implementation of positive reinforcement occurs in conditions in which the standard responses of the unconditioned stimulus are not effective.Целью данной статьи является выяснение особенностей инструментального условного рефлекса как знаковой системы. При становлении условного рефлекса происходит «идеализация» причиняющей способности безусловного раздражителя, которую вбирает в себя знак – условный раздражитель. В классических условных рефлексах действие знака напрямую приводит к подкреплению. Однако, результаты деятельности в классическом условном рефлексе определяются ограниченным набором эффекторных реакций, имеющих сходство с безусловно-рефлекторными. Поэтому часто возникает ситуация, когда деятельность, вызываемая исходной причиной безусловного раздражителя уже не способна приводить к подкреплению. В этом случае достижение подкрепления возможно только за счет появления механизмов, например определенных движений животного, то есть формирования инструментальных условных рефлексов. За счет включения инструментальных реакций в структуру рефлекса отношения между знаком и безусловным раздражителем (подкреплением) усложняются и становятся опосредствованными. Благодаря «идеализации» безусловного раздражителя открываются возможности не только мотивировать рефлекторную деятельность новыми агентами (знаками) с различных анализаторных систем как в классических условных рефлексах, но и мотивировать новые виды деятельности, выходящие за пределы врожденных безусловно-рефлекторных способов реагирования. Эта универсальная способность раздражителя может причинять, мотивировать новые способы действия. Появление инструментальной активности упраздняет безусловно-рефлекторные последствия для организма и формирует новые полезные результаты деятельности в виде полноценного подкрепления

ORIENTAL JOURNAL OF CHEMISTRY Microstructure and Optical Properties of Composites Consisting of Nanoporous Stretched Polypropylene doped with Liquid Crystals and Quantum Dots at a High Concentration

ABSTRACT Unique properties of nanohybrid composites based on different types of porous polymer matrices doped with fluorescent nanoparticles (quantum dots, QDs) are determined by the combination of the mechanical properties of the host matrix (flexibility, chemical stability, etc.) and a high luminescence intensity and extreme stability of QDs. Here, we report on the preparation, optical and microstructural characterization of a nanoporous stretched polypropylene matrix embedded with CdSe/ZnS QDs as fluorescent dopants at a high concentration. The microstructure and optical properties of two types films based on QD-polymer composites and liquid crystals are described. The distribution of QDs in the composite films and their morphology was determined. The annealing of the nanoporous composite films leads to shrinking of the pores and encapsulation of QDs, which results in a domain-like structure. The resulting flexible, stable and highly luminescent materials may be applied to obtain the highly luminescent diodes, the light converter devices and the display systems

Modulation of quantum dot photoluminescence in porous silicon photonic crystals as a function of the depth of their penetration

International audiencePhotonic crystals doped with fluorescent nanoparticles offer a plenty of interesting applications in photonics, laser physics, and biosensing. Understanding of the mechanisms and effects of modulation of the photoluminescent properties of photonic crystals by varying the depth of nanoparticle penetration should promote targeted development of nanocrystal-doped photonic crystals with desired optical and morphological properties. Here, we have investigated the penetration of semiconductor quantum dots (QDs) into porous silicon photonic crystals and performed experimental analysis and theoretical modeling of the effects of the depth of nanoparticle penetration on the photoluminescent properties of this photonic system. For this purpose, we fabricated porous silicon microcavities with an eigenmode width not exceeding 10 nm at a wavelength of 620 nm. CdSe/CdS/ZnS QDs fluorescing at 617 nm with a quantum yield of about 70% and a width at half-height of about 40 nm were used in the study. Confocal microscopy and scanning electron microscopy were used to estimate the depth of penetration of QDs into the porous silicon structure; the photoluminescence spectra, kinetics, and angular fluorescence distribution were also analyzed. Enhancement of QD photoluminescence at the microcavity eigenmode wavelength was observed. Theoretical modeling of porous silicon photonic crystals doped with QDs was performed using the finite-difference time-domain (FDTD) approach. Theoretical modeling has predicted, and the experiments have confirmed, that even a very limited depth of nanoparticle penetration into photonic crystals, not exceeding the first Bragg mirror of the microcavity, leads to significant changes in the QD luminescence spectrum determined by the modulation of the local density of photonic states in the microcavity. At the same time, complete and uniform filling of a photonic crystal with nanoparticles does not enhance this effect, which is as strong as in the case of a very limited depth of nanoparticle penetration. Our results will help to choose the best technology for fabrication of efficient sensor systems based on porous silicon photonic crystals doped with fluorescent nanoparticles

High-resolution 3D structural and optical analyses of hybrid or composite materials by means of scanning probe microscopy combined with the ultramicrotome technique: an example of application to engineering of liquid crystals doped with fluorescent quantum dots

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Polariton-assisted manipulation of energy relaxation pathways: donor–acceptor role reversal in a tuneable microcavity.

International audienceResonant interaction between excitonic transitions of molecules and localized electromagnetic field allows the formation of hybrid light–matter polaritonic states. This hybridization of the light and the matter states has been shown to significantly alter the intrinsic properties of molecular ensembles placed inside the optical cavity. Here, we have observed strong coupling of excitonic transition in a pair of closely located organic dye molecules demonstrating an efficient donor-to-acceptor resonance energy transfer with the mode of a tuneable open-access cavity. Analysing the dependence of the relaxation pathways between energy states in this system on the cavity detuning, we have demonstrated that predominant strong coupling of the cavity photon to the exciton transition in the donor dye molecule can lead not only to an increase in the donor–acceptor energy transfer, but also to an energy shift large enough to cause inversion between the energy states of the acceptor and the mainly donor lower polariton energy state. Furthermore, we have shown that the polariton-assisted donor–acceptor chromophores’ role reversal or “carnival effect” not only changes the relative energy levels of the donor–acceptor pair, but also makes it possible to manipulate the energy flow in the systems with resonant dipole–dipole interaction and direct energy transfer from the acceptor to the mainly donor lower polariton state. Our experimental data are the first confirmation of the theoretically predicted possibility of polariton-assisted energy transfer reversal in FRET systems, thus paving the way to new avenues in FRET-imaging, remote-controlled chemistry, and all-optical switching

Novel cholesteric materials doped with CdSe/ZnS quantum dots with photo- and electrotunable circularly polarized emission

International audienceOptical materials based on cholesteric liquid crystals (LCs) doped with fluorescent CdSe/ZnS quantum dots (QDs) have been developed and demonstrated to have a wide photonic band gap. It has been shown that the fluorescence emission of QDs embedded in LCs is circularly polarized and that the dissymmetry factor of this polarization may be optically or electrically controlled via conformational changes in the helical structure of the LC matrix. The possibility of photochemical patterning or image recording using these materials has been demonstrated; the recorded information can be read through changes in the dissymmetry factor of circular polarization of QDs emission. The developed photo- and electro-active materials with a controlled degree of fluorescence circular polarization may be used as on-demand single photon sources in photonics, optoelectronics, and quantum cryptography, as well as for development of nanophotonic systems capable of low-threshold lasing

A novel design of a scanning probe microscope integrated with an ultramicrotome for serial block-face nanotomography

International audienceWe present a new concept of a combined scanning probe microscope (SPM)/ultramicrotome apparatus. It enables “slice-and-view” scanning probe nanotomography measurements and 3D reconstruction of the bulk sample nanostructure from series of SPM images after consecutive ultrathin sections. The sample is fixed on a flat XYZ scanning piezostage mounted on the ultramicrotome arm. The SPM measuring head with a cantilever tip and a laser-photodiode tip detection system approaches the sample for SPM measurements of the block-face surface immediately after the ultramicrotome sectioning is performed. The SPM head is moved along guides that are also fixed on the ultramicrotome arm. Thereby, relative dysfunctional displacements of the tip, the sample, and the ultramicrotome knife are minimized. The design of the SPM head enables open frontal optical access to the sample block-face adapted for high-resolution optical lenses for correlative SPM/optical microscopy applications. The new system can be used in a wide range of applications for the study of 3D nanostructures of biological objects, biomaterials, polymer nanocomposites, and nanohybrid materials in various SPM and optical microscopy measuring modes