Electroluminescent Structures Research Articles

Integration of blue–green electroluminescence structure in mid-infrared hollow optical fiber for targeting invisible CO2 laser beam

Mid-infrared (IR) CO2 lasers have important applications in laser medicine and material processing. However, the CO2 laser beam is invisible to human eyes, it is not easy to accurately indicate the beam position in practical applications. In this work, we designed a PEDOT (Poly (3, 4-ethylenedioxythiophene))/ZnS: Cu/BaTiO3/Ag electroluminescence (EL) structure and integrated it at the output end of the mid-IR hollow optical fiber. The blue–green light can be output along with the CO2 laser beam in this EL structure integrated fiber, thus achieving the optical path indication and illumination of invisible laser beam. This work provides a possible guide for aiming the CO2 laser beam in the min-IR optical fiber.

Optimising the electroluminescence performance of ZnS: Cu/epoxy composites via exploring the relationship between electroluminescence intensity and filler intrinsic attributes

Electroluminescent composites have considerable potential for applications in photoelectric display, electric field measurement and other fields due to their advantages of simple preparation and uniform luminescence. However, high voltage required by the operation of electroluminescent composites hinders their applications in the electric domain, and research on the relationship between electroluminescence principle of composites and filler intrinsic attributes is insufficient. In this paper, the effects of electric field strength, filler mass fraction and voltage frequency on the electroluminescence intensity of ZnS: Cu/epoxy composites are studied, which are majorly used as the luminescent layer of electroluminescent devices. To enhance the electroluminescence intensity of composites, high-temperature sintered BaTiO3 and zinc oxide whiskers (ZnOw) particles are introduced in the base matrix. The finite element method is applied to verify that the matrix of high dielectric constant is in favour of improving the electroluminescence intensity of composites. The band structure of the ZnS: Cu particle is calculated based on the density functional theory + U method to analyse the intrinsic relationship between electroluminescence and particle electronic structure. This paper provides a basis for the research of high electroluminescence intensity devices and will be conducive to better understanding on the relationship between electroluminescence principle and filler intrinsic attributes.

ОСОБЛИВОСТІ ВИБОРУ ДІЕЛЕКТРИЧНИХ ШАРІВ ДЛЯ ЕЛЕКТРОЛЮМІНЕСЦЕНТНИХ СТРУКТУР

The paper considers an equivalent scheme of a thin-film electroluminescent emitter (TFELE), taking into account dielectric leaks, and proposes a criterion for the optimal choice of a dielectric in the structure to increase its efficiency. A calculation method is proposed for the optimal choice of material for dielectric films in an electroluminescent structure, taking into account their dielectric loss tangent. The algorithm for optimizing the parameters is based on the method of pairwise comparison of two dielectrics, provided that the charge flowing through the structure is constant or increased. The calculated data for materials are given in the form of a table according to the sequence of deterioration of their characteristics. The most attractive of the materials considered are PbTiO3, Ta2O5, Y2O3, as well as improved ceramics, which is confirmed by experiment. The possibility of applying the proposed model to explain the dependence of the luminosity of electroluminescent emitters on their excitation voltage is shown. A comparative analysis of the results of the calculation and experiment of the dependence of brightness on the applied voltage (B-V) for three types of TFELE based on a luminescent layer ZnS : Mn (0.5%) with a thickness of 0.6 μm, placed between two dielectric layers with a thickness of about 0.3- 0.35 μm with Ta2O5, Sm2O3 and Y2O3, respectively. It is established that the threshold luminescence excitation voltage correlates with the value of εE, and the maximum brightness with the value of εE / tg (δ). The table also shows the calculated characteristics of NdAlO3 and AlN films deposited by high-frequency magnetron sputtering. Higher brightness values can be expected from electroluminescent structures with such a dielectric than from structures with dielectric films with Sm2O3 and Y2O3. The results of such studies are presented in the form of a graph and table. This method can find practical application in the development of new materials and technologies for their production.

Formulation of the modern indicator devices modelling problem

This work is dedicated to study of the structural characteristics and parameters in advanced electroluminescent structures. The important problems in this area are the high complexity and the slowness of the design calculation processes. The problem can be solved by developing a mathematical model of the system based on equivalent circuits. First step in developing a mathematical model is formulation.

Influence of post annealing treatments on the luminescence of rare earth ions in ZnO:Tb,Eu/Si heterojunction

(Tb, Eu)–co-doped ZnO films with about 3 at.% total doping rate were grown by magnetron sputtering on Si substrate. Post annealing treatments were performed at 973–1373 K in continuous nitrogen flow to investigate the transformation of microstructural and optical characteristics by means of X-ray diffraction, transmission electron microscopy, photoluminescence and electroluminescence. For annealing temperatures lower than 1073 K, segregation of Eu and Tb was observed mainly at the film/substrate junction. For temperatures higher than 1173 K, additional phases appeared, namely, Zn2SiO4 and rare earth silicates. For the highest temperature investigated (1373 K), only silica and rare earth silicates remained in the film due to Zn evaporation. PL measurements indicated a very intense Eu emission associated with the presence of rare earth silicate inclusions. Energy transfer from Tb towards Eu was evidenced in this secondary phase. At last, based on these preliminary works, a (Tb, Eu)–co-doped ZnO/Si electroluminescent structure was produced and showed very promising results paving the way for very thin ZnO based light emitting diodes.

Electroluminescence Spectra and Structure of Anodic Aluminum Oxide Upon Its Formation in Chemically Pure Water and Alcohols

Electroluminescence Spectra and Structure of Anodic Aluminum Oxide Upon Its Formation in Chemically Pure Water and Alcohols

Electricity−free electroluminescence excited by droplet impact driven triboelectric field on Solid−Liquid interface

In this work, a novel solid-liquid interfacing triboelectric field based electroluminescence (SL-TEL) was proposed. When a droplet impacting on the SL-TEL device surface, specific textured green SL-TEL emit on the two cross-overlapped areas. As a coupling effect of solid-liquid interfacing triboelectrification and electroluminescence, the SL-TEL is essentially a type of electroluminescence excited by changing triboelectric field of droplet impact or wave scour. It relies on converting mechanical energy of liquid to visual light energy utilizing an intermediate triboelectric field without any electric power consumption. The SL-TEL device simply consist of three thin flexible layers, which is greatly simplifying the electroluminescent device structure and showing strong advantages of simple structure such as easy to integration and excellent stability. Experiments show that sequential liquid motions of droplet impinging on solid surface excite a corresponding dynamic series of electroluminescence patterns. The features of the electroluminescence also reveal the characteristics of liquid and the solid surface, such as contour edge of liquid spreading, capillary convergence of liquid at the apex (advancing and receding), and so on, which is capable of both sensing liquid leakage and displaying the dynamic information of droplets impacting motions.

Stretchable and Washable Electroluminescent Display Screen-Printed on Textile.

Stretchable polymer composites are a new group of materials with a wide range of application possibilities in wearable electronics. The purpose of this study was to fabricate stretchable electroluminescent (EL) structures using developed polymer compositions, based on multiple different nanomaterials: luminophore nanopowders, dielectric, carbon nanotubes, and conductive platelets. The multi-layered EL structures have been printed directly on textiles using screen printing technology. During research, the appropriate rheological properties of the developed composite pastes, and their suitability for printed electronics, have been confirmed. The structure that has been created from the developed materials has been tested in terms of its mechanical strength and resistance to washing or ironing.

Electroluminescence and contact formation of 1-(pyridin-2-yl)-3-(quinolin-2-yl)imidazo[1,5-a]quinoline thin films

Abstract Contact formation was investigated for the recently introduced organic light emitting molecule 1-(pyridin-2-yl)-3-(quinolin-2-yl)imidazo[1,5-a]quinoline (PCIC) by in situ atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) during physical vapor deposition (PVD). The hole conductors poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and poly(9-vinylcarbazole) (PVK), as well as the electron conductor bathocuproine (BCP) were used. Different growth modes were found for PCIC films and charge carrier injection barriers were identified. Based on these findings, electroluminescent layer structures with an imidazo[1,5-a]quinoline were prepared for the first time and effects of contact formation on radiative recombination were studied. Depending on the chosen contact material, blue PCIC electroluminescence or significantly red-shifted emission presumably caused by electroplex formation could be obtained. Using PCIC in a host-guest system within a matrix of PVK and 1,3-bis[5-(4-tert-butylphenyl)-2-[1,3,4]oxadiazolyl]benzene (Oxd-7), led to blue emission at improved luminescence. The studied interactions of PCIC with typical contact materials reveal the potential and limitations to use PCIC as an electroluminescent material.

Creation and Investigation of Organic Light-Emitting Structures Containing Arrays of Colloidal Quantum Dots

We have created organic electroluminescent structures—ITO/TPD/Alq3/Al and ITO/PEDOT:PSS/TPD/Alq3/Al—which are organic light-emitting diodes (OLEDs). Experiments on the incorporation of CdSe/ZnS colloidal quantum dots into the active layer of the structure have been performed. The parameters of the created structures have been determined using optical-spectroscopy methods. The appropriateness of using the method of high-speed vacuum thermal deposition as a main method for the deposition of structural layers has been demonstrated, and the possibility of accelerated formation of layers of the material without disturbing its chemical structure has been shown. By measuring the photoluminescence spectra at different points in samples, we have determined the quality of the obtained structures and plotted maps of the radiation power distribution of the material and of its thickness. Recommendations for the creation of upper contacts and other regions of light-emitting structures have been formulated. We have created organic structures with ITO/PEDOT:PSS/TPD/TPD + CQD’s CdSe/Alq3/Al colloidal quantum dots, in which electroluminescence of CdSe/ZnS quantum dots has been obtained for a wide range of applied voltages. It has been shown that the introduction of colloidal quantum dots into the structure leads to a significant modification of its electroluminescence spectrum.

Photodielectric Processes in ZnS : Cu Polycrystalline Layers

The frequency dependences of dielectric parameters of zinc sulfide electroluminescent polycrystalline structures doped with copper are studied in the dark and under light excitation in the visible wavelength range. A positive photodielectric effect most pronounced in the low-frequency range was revealed. The experimental results are explained within framework of formation of a space charge in the bulk of a semiconductor. The analysis of data indicates they can be correlated with luminance characteristics of an electroluminescent layer.

Фотодиэлектрические процессы в поликристаллических слоях ZnS:Cu

AbstractThe frequency dependences of dielectric parameters of zinc sulfide electroluminescent polycrystalline structures doped with copper are studied in the dark and under light excitation in the visible wavelength range. A positive photodielectric effect most pronounced in the low-frequency range was revealed. The experimental results are explained within framework of formation of a space charge in the bulk of a semiconductor. The analysis of data indicates they can be correlated with luminance characteristics of an electroluminescent layer.

Ultrafast Laser Pulses for Structuring Materials at Micro/Nano Scale: From Waveguides to Superhydrophobic Surfaces

The current demand for fabricating optical and photonic devices displaying high performance, using low-cost and time-saving methods, prompts femtosecond (fs)-laser processing as a promising methodology. High and low repetition femtosecond lasers enable surface and/or bulk modification of distinct materials, which can be used for applications ranging from optical waveguides to superhydrophobic surfaces. Herein, some fundamental aspects of fs-laser processing of materials, as well as the basics of their most common experimental apparatuses, are introduced. A survey of results on polymer fs-laser processing, resulting in 3D waveguides, electroluminescent structures and active hybrid-microstructures for luminescence or biological microenvironments is presented. Similarly, results of fs-laser processing on glasses, gold and silicon to produce waveguides containing metallic nanoparticles, analytical chemical sensors and surface with modified features, respectively, are also described. The complexity of fs-laser micromachining involves precise control of material properties, pushing ultrafast laser processing as an advanced technique for micro/nano devices.

Patch antenna microcavity terahertz sources with enhanced emission

We study the emission properties of an electroluminescent THz frequency quantum cascade structure embedded in an array of patch antenna double-metal microcavities. We show that high photon extraction efficiencies can be obtained by adjusting the active region thickness and array periodicity as well as high Purcell factors (up to 65), leading to an enhanced overall emitted power. Up to a 44-fold increase in power is experimentally observed in comparison with a reference device processed in conventional mesa geometry. Estimation of the Purcell factors using electromagnetic simulations and the theoretical extraction efficiency are in agreement with the observed power enhancement and show that, in these microcavities, the overall enhancement solely depends on the square of the total quality factor.

Maleimide–based donor-π-acceptor-π-donor derivative for efficient organic light-emitting diodes

Herein, we report a highly fluorescent material 3,4-bis(4′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-4-yl)-1-hexyl-1H-pyrrole-2,5-dione (Cbz-MI) based on donor-π-acceptor-π-donor (D-π-A-π-D) backbone. We explored maleimide as an acceptor, phenyl as π-conjugated spacer and carbazole as donor. Photophysical properties revealed high photoluminescence quantum yield of 0.84 and 0.72 in solution and doped matrix, respectively. An encouraging external quantum efficiency of 2.5% with emission peak at 550 nm is achieved utilizing Cbz-MI as emitting layer in doped electroluminescent device structure.

II-VI Quantum Cascade emitters in the 6-8μm range.

We present the growth and characterization of ZnCdSe/ZnCdMgSe quantum cascade (QC) heterostructures grown by molecular beam epitaxy (MBE) and designed to operate at 6-8μm. These structures utilize the better-understood ZnCdMgSe with InP lattice matched compositions yielding a bandgap of 2.80 eV as compared to previous work which used ZnCdMgSe compositions with bandgaps at 3.00 eV. Grown structures posses good structural and optical properties evidenced in X-ray diffraction and photoluminescence studies. Fabricated mesa devices show temperature dependent I-V measurements with differential resistance of 3.6 Ω, and a turn on voltage of 11V consistent with design specifications. Electroluminescence was observed in these devices up to room temperature with emission centered at 7.1 μm and line widths of ∼16%(ΔE/E) at 80K. The results show that these are well-behaved electroluminescent structures. Addition of waveguide layers and further improvements in well barrier interfaces are being pursued in efforts to demonstrate lasing.

Transparent and Flexible Thin Film Electroluminescent Devices Using HiTUS Deposition and Laser Processing Fabrication

Highly transparent thin film electroluminescent structures offering excellent switch on characteristics, high luminance and large break-down voltages have been deposited onto glass and flexible polymeric materials with no substrate heating using high target utilization sputtering. Deposition of ZnS:Mn as the active light emitting layer and Y2O3, Al2O3, Ta2O5, and HfO2 as dielectric materials arranged in single and multiple layer configurations were investigated. Devices incorporating Al2O3, HfO2 quadruple layers demonstrate the highest attainable luminance at low threshold voltage. Single pulse excimer laser irradiation of the phosphor layer prior to deposition of the top dielectric layer enhanced the luminance of the devices. The devices fabricated on glass and polymeric substrates exhibited a maximum luminance of 500 and 450 cdm $^{-2}$ when driven at $270~{\mathrm{ V}}_{\mathrm{ RMS}} $ and $220~{\mathrm{ V}}_{\mathrm{ RMS}} $ , respectively, with a 1.0 kHz sine wave.

Analysis of and increase in working time of electroluminescence panels

Possible reasons for decomposition of the emission layer of working electroluminescence structures that cause a decrease in the working time are considered. Results of a multifactor experiment aimed at a search for the optimal composition of suspensions of the emitting and dielectric layers of the structure are presented. Compositions of dielectric components are proposed. Results of life tests are presented.

Influence of the Temperature as an Environmental Factor on the Electrophysical Behavior of Flexible Polymeric Luminescent Devices

The effect of operational temperature on the electrophysical properties of polymer based electroluminescent structures is examined. For this purpose thin film of light-emitting semiconductor polyphenylenevinylene derivative is deposited between two indium-tin oxide (ITO) electrodes. DC current-voltage (I-V) characteristics of the fabricated devices ITO/polyphenylenevinylene derivative PPV-D/ITO are measured at varying ambient temperatures, ranging from room temperature (25°C) to 70°C. Several important electrical parameters like a trap factor, traps activation energy distribution, free carriers’ density, trapped carriers density, and effective mobility are estimated from measured temperature dependent I-V curves. Such analysis of the charge transport process in polymer devices may give information needed for optimization of the existing structures.

Synthesis, crystal structure, and electroluminescent properties of zinc and cadmium tetradentate azomethine complexes

Chemical and electrochemical syntheses of zinc(II) and cadmium(II) complexes based on tetradentate Schiff bases (H2L1 and H2L2) resulting from condensation of 2-tosylaminobenzaldehyde with 3,6-dioxa-1,8-octanediamine or 4,9-dioxa-1,12-dodecanediamine were performed. The structure, composition, and properties of the complexes were studied by elemental analysis, IR, 1H NMR, and UV spectroscopy, X-ray absorption spectroscopy, and X-ray diffraction. The zinc(II) and cadmium(II) complexes luminesce in a DMF solution in the blue spectral region (λPL = 425–433 nm), the photoluminescence quantum yield φ being 0.25–0.30. Multilayer zinc(II)- and cadmium(II)-based electroluminescent structures with green-blue emission of the exciplex nature were fabricated.