Direct imaging of fluorescence enhancement in the gap between two gold nanodisks

We present an analysis of the optical coupling between two gold nanodisks by near-field fluorescence microscopy. This is achieved by simultaneously scanning and measuring the light emitted by a single Er3þ/Yb3þ doped nanocrystal glued at the end of an atomic force microscope tip. The excitation of the nanocrystal was performed at k ¼ 975 nm via upconversion, and fluorescence was detected in the visible part of the spectrum at k ¼ 550 nm. For an isolated nanodisk, the near-field presents a two-lobe pattern oriented along the direction of the incident polarization. For two nanodisks with a sizable separation distance (385 nm) illuminated with the polarization along the interparticle axis, we observe a negative effect of the coupling with a slight decrease in fluorescence in the gap. For smaller gap values (195, 95, and 55 nm), a strong increase in fluorescence is observed as well as a reduced spatial localization of the field as the distance decreases. Finally, when the disks touch each other (0 nm), the dipolar–dipolar interaction between them disappears and no fluorescence enhancement occurs. A new plasmon mode is created at another wavelength. Our experimental results are in good agreement with numerical simulations of the nearfield intensity distribution at the excitation wavelength on the surface of the structures. Combining fluorescence mapping and far-field scattering spectroscopy should be of strong interest to develop bio-chemical sensors based on field enhancement effects.The authors thank the support from the DIM Nano-K program from “Region Ile de France,” from the Idex Paris Sciences & Lettres through Grant No. ANR-10-IDEX-0001-02 PSL from the CNRS and the CSIC through the Spanish-French program PICS (Grant Nos. SolarNano PICS07687 and PIC2016FR2), and from the Spanish Ministerio de Ciencia e Innovacion through Grant No. PID2019-109905GA-C22.Peer reviewe

Roadmap on Perovskite Light-Emitting Diodes

In recent years, the field of metal-halide perovskite emitters has rapidly emerged as a new community in solid-state lighting. Their exceptional optoelectronic properties have contributed to the rapid rise in external quantum efficiencies (EQEs) in perovskite light-emitting diodes (PeLEDs) from <1% (in 2014) to approaching 30% (in 2023) across a wide range of wavelengths. However, several challenges still hinder their commercialization, including the relatively low EQEs of blue/white devices, limited EQEs in large-area devices, poor device stability, as well as the toxicity of the easily accessible lead components and the solvents used in the synthesis and processing of PeLEDs. This roadmap addresses the current and future challenges in PeLEDs across fundamental and applied research areas, by sharing the community's perspectives. This work will provide the field with practical guidelines to advance PeLED development and facilitate more rapid commercialization.Comment: 103 pages, 29 figures. This is the version of the article before peer review or editing, as submitted by an author to Journal of Physics: Photonics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

Nanocristaux colloïdaux appliqués aux photodétecteurs infrarouges à ondes courtes avec réponse apide

Short-wave infrared (SWIR) typically refers to the photons in the wavelength range from 1 to 3 micrometers. Applications in this wavelength window exploit various advantages such as long penetration length in biological tissue, spectral coverage of the atmospheric nightglow, and the characteristic excitation energy of certain molecular vibration modes. SWIR photodetectors are thus the key technological components to achieve optical communication, environmental gas sensing, biodiagnostics, and passive night vision. Current SWIR technologies mainly rely on low-bandgap compound semiconductors, such as InGaAs, InSb, PbS, and HgCdTe. While classical SWIR photodetectors exhibit excellent detectivity, they are costly (due to epitaxial growth requirement) and/or environment unfriendly involving highly toxic elements. There are, therefore, continuous research and development efforts for alternative material systems and fabrication methods to expand the scope of applications of SWIR photodetection. In recent years, many new materials have been proposed, including black phosphorus, graphene, MoS2, and colloidal PbS nanocrystals. They show great promise in terms of operation at high modulation frequencies or high sensitivity. But some disadvantages still keep them away from the market: rigorous production process (poor reproducibility), non-adaptability to scale-up fabrication, manufactory safety and security concerns (due to the use of highly toxic elements). Alternatively, solution-processed colloidal nanoparticles, such as colloidal gold nanorods (Au NRs) and upconversion nanoparticles (UCNPs), exhibit interesting characteristics possible to overcome these disadvantages: capability of scaling-up synthesis, solution-processability adaptable to low-cost fabrication, high stability, low biological toxicity, and good optical absorption for SWIR photons. This PhD thesis aims to apply these colloidal nanoparticles to fabricate SWIR photodetectors and verifies their possibilities for new generation of photodetection. A few SWIR photodetectors (Au-NRs/Thermistor, Au-NRs/Pt photodetector and UCNPs/Polymers photodetector) were developed in this work, showing high responsivity and sensitivity. In addition, the preparation of these devices is a low-cost and scalable up to mass production process both in the materials synthesis and device fabrication, opening a new and convenient path to the next-generation SWIR photodetectors.L'infrarouge à ondes courtes (SWIR) désigne généralement les photons dans la plage de longueurs d'onde allant de 1 à 3 micromètres. Les applications dans cette fenêtre de longueur d'onde exploitent divers avantages tels qu’une grande longueur de pénétration dans le tissu biologique, la couverture spectrale pour la vision nocturne atmosphérique et l'énergie d'excitation caractéristique de certains modes de vibration moléculaire. Les photodétecteurs SWIR sont donc les composants technologiques essentiels pour la communication optique, la détection de gaz dans l’environnement, le biodiagnostic et la vision nocturne passive. Les technologies SWIR actuelles reposent principalement sur des semi-conducteurs composés à faible bande interdite, tels que InGaAs, InSb, PbS et HgCdTe. Alors que les photodétecteurs SWIR classiques présentent une excellente détectivité, ils sont coûteux (en raison de la croissance requise par l'épitaxie) et / ou présentent un risque environnemental car impliquant des éléments hautement toxiques. Par conséquent, des efforts continus en matière de recherche et de développement concernant des systèmes de matériaux alternatifs et des méthodes de fabrication permettant d'élargir le champ des applications de la photodétection SWIR sont en cours. Ces dernières années, de nombreux nouveaux matériaux ont été proposés, notamment les nanocristaux de phosphore noir, de graphène, de MoS2 et de PbS colloïdal. Ils sont très prometteurs en termes de fonctionnement à des fréquences de modulation élevées et avec une excellente sensibilité. Cependant, certains inconvénients les éloignent toujours du marché: processus de production difficile (faible reproductibilité), non-adaptabilité à la fabrication à grande échelle, préoccupations de sécurité lors de la production en usine (en raison de l’utilisation d’éléments hautement toxiques). Alternativement, les nanoparticules colloïdales traitées en solution, telles que les nanorods d’or colloïdal (Au NR) et les nanoparticules fonctionnant par up-conversion (UCNP), présentent des caractéristiques intéressantes permettant de surmonter ces inconvénients: capacité de synthèse et de production à grande échelle et à faible coût, haute stabilité, faible toxicité biologique et bonne absorption optique des photons SWIR. Cette thèse a pour objectif d'appliquer ces nanoparticules colloïdales à la fabrication de photodétecteurs SWIR et d’étudiere des possibilités d’application dans le domaine de la photodétection. Quelques photodétecteurs SWIR (Au-NRs / Thermistance, photodétecteur Au-NRs / Pt et photodétecteur UCNPs / Polymers) ont été développés dans ce travail, montrant une sensibilité élevées. De plus, la fabrication de ces dispositifs est un procédé peu coûteux et évolutif vers la production de masse au niveau de la fois à la synthèse des matériaux et de la fabrication des composants, et ouvre une nouvelle voie sur le marché de la prochaine génération de photodétecteurs

Design and Comparative Study of a Small-Stroke Energy Harvesting Floor Based on a Multi-Layer Piezoelectric Beam Structure

Recently, research on the energy harvesting floor is attracting more and more attention due to its possible application in the smart house, invasion monitoring, internet of things, etc. This paper introduced a design and comparative study of a small-stroke piezoelectric energy harvesting floor based on a multi-layer piezoelectric beam structure. The multi-layer piezoelectric beams are designed based on simply supported beams in an interdigitated manner. Theoretical analysis is explored to find out the beam number and layer number of the structure. Through this design, the input power from the human footsteps was effectively utilized and transformed into electrical power. The designed piezoelectric energy harvesting floor structure was tested by our designed stepping machine, which can simulate the stepping effect of a walking human on the floor with different parameters such as stepping frequency. Comparative studies of the energy harvester are carried out regarding different stepping frequencies, external circuits, and initial beam shapes. The experimental results showed that the maximum output power of a group of four-layer prototypes was 960.9 µW at a stroke of 4 mm and a step frequency of 0.83 Hz, with the beams connected in parallel

An open source SDR-based NOMA system for 5G networks

With the rapid advent of various new applications and services, the anticipated use of bandwidth and frequency resources is beyond expectation in future mobile networks. To maximize spectral efficiency, novel radio access techniques need to multiplex users in the most suitable combinations of frequency and radio resources. Non-orthogonal multiple access (NOMA) is one of the candidate radio access techniques for improving spectral efficiency in the 5G mobile network through multiplexing users in the power domain, which has never been explored in past and current communications systems. While the concept of NOMA was proposed several years ago, the performance of NOMA has only been verified in theory but not in practice. In this article, we first introduce the state of the art in open source SDR. Due to the high flexibility and reconfigurability of open source SDR, we choose general-purpose-processor-based SDR to implement our NOMA system, which is based on an open source LTE program. Over-the-air experiments are carried out on the designed NOMA system for the purpose of performance evaluation, and to demonstrate its potential in future 5G mobile networks

Nanoscale thermal characterization of high aspect ratio gold nanorods for photothermal applications at λ = 1.5 μ m

International audienceWe synthetized gold nanorods that present a high aspect ratio (>10) and possess a surface plasmon resonance in the near-infrared, in the 1300–1600 nm spectral range. Using a single Er3+-doped NaYF4 nanocrystal deposited on their surface, we measured the temperature increase of a few nanorods excited at their surface plasmon resonance wavelength. We observed a temperature increase of more than 30 °C for an excitation power density of 3 mW/μm2. This experiment shows that a very small amount of nanorods can be used for obtaining an intense and localized photothermal effect. Applications can be found in the design of inexpensive infrared photodetectors and photothermal therapy in the third biological window. In addition, the association of gold nanorods with an Er3+ doped nanocrystal constitutes a very interesting hybrid heater/temperature sensor

Hybrid plasmonic gold-nanorod–platinum short-wave infrared photodetectors with fast response

International audienceShort-wave infrared (SWIR) photodetectors, sensitive to the wavelength range between 1 and 3 μm, are essential components for various applications, which constantly demand devices with a lower cost, a higher responsivity and a faster response. In this work, a new hybrid device structure is presented for SWIR photodetection composing a coupling between solution-processed colloidal plasmonic gold (Au) NRs and a morphology-optimized resistive platinum (Pt) microwire. Pt microwires harvest efficiently the photothermal effect of Au NRs and in return generating a change of device resistance. A fast photon-heat-resistance conversion happens in these Au-NRs/Pt photodetectors exhibiting a response (rise) time of 97 μs under the illumination of a λ = 1.5 μm laser. Clear photoresponse can be observed in these devices at a laser illumination with a modulation frequency up to 50 kHz. The photoresponsivity of the current devices reached 4500 Ω W−1 under a laser power of 0.2 mW, which is equivalent to a responsivity of 340 mA W−1 under a DC bias of 1 V. A series of mapping experiments were performed providing a direct correlation between Au NRs and the device zone where resistance change happens under a laser illumination modulated at different frequencies

Heavy-Metal-Free Flexible Hybrid Polymer-Nanocrystal Photodetectors Sensitive to 1.5 μm Wavelength

International audiencePhotodetection in the short-wave infrared (SWIR) wavelength window represents one of the core technologies allowing for many applications. Most current photodetectors suffer from high cost due to the epitaxial growth requirements and the ecological issue due to the use of highly toxic heavy-metal elements. Toward alternative SWIR photodetection strategies, in this work, high-performance heavy-metal-free flexible photodetectors sensitive to λ = 1.5 μm photons are presented based on the formation of a solution-processed hybrid composed of a conjugated diketopyrrolopyrrole-base polymer/PC70BM bulk heterojunction organic host together with inorganic guest NaYF4:15%Er3+ upconversion nanoparticles (UCNPs). Under the illumination of λ = 1.5 μm SWIR photons, optimized hybrid bulk-heterojunction (BHJ)/UCNP photodetectors exhibit a photoresponsivity of 0.73 and 0.44 mA/W, respectively, for devices built on rigid indium tin oxide (ITO)/glass and flexible ITO/polyethylene terephthalate substrates. These hybrid photodetectors are capable of performing SWIR photodetection with a fast operation speed, characterized by a short photocurrent rise time down to 80 μs, together with an excellent mechanical robustness for flexible applications. Exhibiting simultaneously multiple advantages including solution-processability, flexibility, and the absence of toxic heavy metal elements together with a fast operation speed and good photoresponsivity, these hybrid BHJ(DPPTT-T/PC70BM)/UCNP photodetectors are promising candidates for next-generation low-cost and high-performance SWIR photodetectors

Electron donor–acceptor (D-A) tuning to achieve soluble covalent organic polymers for optoelectronic devices

Covalent organic polymers (COPs) have emerged as a unique class of luminescent polymers with pre-designed quasi-ordered architectures. However, their layered stacks and limited solubility preclude further processing for large-scale applications in devices, especially optoelectronic equipment. Herein, a universal strategy to adjust the electron donor–acceptor (D-A) moieties of the building blocks in COPs is proposed, achieved by in situ charge exfoliation of COP blocks into few-layer true solutions in (Lewis) acid and base media. The electron D-A moieties of the building blocks endow the COPs with the ability to accept or donate electrons, by altering the electron cloud distribution as well as the relative energy levels of the frontier molecular orbitals. The resultant soluble COPs can easily be processed into a uniform film by solution processing via the spin-coat method. The obtained COP-N achieves efficient and stable perovskite electroluminescence as a novel hole injection material on indium tin oxide, and the operating lifetime for a perovskite quantum dot light-emitting diodes device exceeds that of a poly(ethylene dioxythiophene):polystyrene sulphonate counterpart. This straightforward electronic regulation strategy provides a new avenue for the rational synthesis of processable reticular molecular polymers for practical electronic devices