Electroluminescent Phosphors Research Articles

Multifunctional Soft Actuator Based on Dielectric Liquid with Simultaneous Luminance and Weight Lifting Capabilities

AbstractSoft robots require soft actuators for mobility and functionality. To integrate multiple functions in a limited space, researchers are developing multifunctional soft actuators with several functions integrated in one device. This study successfully demonstrates an electroluminescent (EL) soft actuator, a single device with both light‐emitting and actuating capabilities, using liquid dielectric and uniformly dispersed EL phosphor particles. EL phosphor particles are copper‐doped zinc sulfide (ZnS) particles doped with copper. The work is able to disperse the ZnS particles uniformly in the oil by coating the ZnS particles with silica, ensuring consistent luminescence across the device's active area. The performance of the soft actuator is notable, with a strain of 25% and a maximum EL intensity of 23 cd m−2 for a single actuator. When stacking multiple actuators, the intensity exceeds 29 cd m−2. The findings suggest that EL actuator devices will be valuable smart components for soft robots and interactive sensors. They can effectively represent external stimuli through color signals, expanding the capabilities of these systems.

Film characteristics of ZnS:Mn phosphor prepared by metal precursor sulfurization and its application to inorganic electroluminescent devices

A ZnS:Mn phosphor film for an inorganic electroluminescent (EL) device fabricated by metal precursor sulfurization was evaluated. Metallic ZnMn was thermally evaporated at room temperature and then sulfurized by sulfur gas flowing in a tube furnace at various temperatures from 400 to 800 °C. X-ray diffraction, energy dispersive x-ray spectroscopy, and photoluminescence observations indicated that a ZnS:Mn phosphor layer was formed after sulfurization. A thick-dielectric EL device was manufactured using the obtained ZnS:Mn phosphor. The EL luminance of 216 cd/m2 at 1.0 kHz was measured when the phosphor layer was sulfurized at 500 °C. A charge density versus voltage (Q-V) curve was also analyzed to evaluate the EL phosphor characteristics.

Blue and white light modulation of a flexible electroluminescent device based on phosphors.

Flexibility, certain mechanical strength, and color modulation are significant elements for flexible optoelectronic devices. However, it is laborious to fabricate a flexible electroluminescent device with balanceable flexibility and color modulation. Here, we mix a conductive nonopaque hydrogel and phosphors to fabricate a flexible alternating current electroluminescence (ACEL) device with color modulation ability. This device realizes flexible strain based on polydimethylsiloxane and carboxymethyl cellulose/polyvinyl alcohol ionic conductive hydrogel. The color modulation ability is achieved by varying the voltage frequency applied on the electroluminescent phosphors. The color modulation could realize blue and white light modulation. Our electroluminescent device exhibits great potential in artificial flexible optoelectronics.

Highly Stretchable Sound-in-Display Electronics Based on Strain-Insensitive Metallic Nanonetworks.

The growing importance of human–machine interfaces and the rapid expansion of the internet of things (IoT) have inspired the integration of displays with sound generation systems to afford stretchable sound‐in‐display devices and thus establish human‐to‐machine connections via auditory system visualization. Herein, the synchronized generation of sound and color is demonstrated for a stretchable sound‐in‐display device with electrodes of strain‐insensitive silver nanowires (AgNWs) and emissive layers of field‐induced inorganic electroluminescent (EL) phosphors. In this device, EL phosphors embedded in a dielectric elastomer actuator (DEA) emit light under alternating‐current bias, while audible sound waves are simultaneously generated via DEA actuation along with input sound signals. The electroluminescence and sound‐generation performances of the fabricated device are highly robust and reliable, being insensitive to stretch‐release cycling because of the presence of the AgNW stretchable electrodes. The presented principle of integrating light emission and acoustic systems in a single stretchable device can be further expanded to realize sound‐in‐display electronics for IoT and human–machine interface applications.

Fabrication of electroluminescent carbon fiber composite for damage visualization

Conventional damage inspection methods and characterization of carbon fiber (CF) composites are typically destructive, expensive, and do not provide spatial resolution. Non-destructive monitoring of carbon fiber composites is presented with an electroluminescent (EL) thin-film dielectric phosphor sandwiched between compacted and semi-transparent dispersed CF composite lamina. Different fractural states in the CF composite cause EL luminance changes which allows for damage detection and localization in the CF through visual inspection. The proposed methodology offers simple and effective structural health monitoring to any product manufactured from CF ranging from aerospace to high-performance sporting goods.

A self-healing and stretchable light-emitting device

A self-healing and stretchable electroluminescent device is developed from an electroluminescent phosphor sandwiched between two aligned carbon nanotube/polyurethane composite electrodes.

Photomechanical modification of ZnS microcrystal to enhance electroluminescence by ultrashort-pulse laser processing

A ZnS microcrystal was treated with an ultrashort-pulse laser and applied to an inorganic electroluminescence (EL) phosphor. We found that the emission intensity of the EL phosphor was increased by laser-induced photomechanical modification. The pulse duration dependence of the emission enhancement and structural analysis by scanning electron microscopy indicated that the structural modification was induced inside the ZnS microcrystal, although a mechanical grinding would induce the structural modification mainly on the crystal surface. The results suggested a new way of enhancing the emission of inorganic EL devices.

Optimization of processing parameters for designing an efficient AC driven powder electroluminescent device

This paper reports various critical processing parameters for the development of efficient ZnS doped with Cu, Al phosphors optimized to exhibit AC electroluminescence. Different firing atmospheres and temperatures were used for the synthesis of electroluminescent phosphor materials. As synthesized ZnS: Cu, Al phosphor powders were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Photoluminescence (PL) and Electroluminescence (EL) spectroscopy studies. Average crystallite size calculated from XRD lies in a range of 44–49µm and average grain size as revealed by SEM lies in the range 3–5µm. The results showed that the phosphor powders have hexagonal phase and exhibit near band edge luminescence in the blue region. This is one of very few reports that depict the observation of EL from hexagonal ZnS:Cu,Al phosphor system. Polycrystalline powders emit PL in a broad band with a maximum at 2.53–2.74eV above the valence band. The PL spectrum of the ZnS:Cu,Al phosphor showed emission peaks at 453nm, 467nm, 485nm and 490nm that could be attributed to the generation of deep level energy traps. The prototype of an alternating current driven thick (40±2µm) film EL device has been fabricated and the threshold voltage was observed to be around 95–120V at a frequency of 1kHz. The critical processing parameters for designing an efficient EL device have been highlighted and discussed thoroughly in the current paper.

Preparation of core/shell luminescent structures by ion-plasma deposition

We have investigated the preparation of encapsulating oxide coatings on the surface of the commercially available copper-doped zinc sulfide electroluminescent phosphor E-455 by ion-plasma deposition. The encapsulants used were titanium, zirconium, and magnesium oxides. In our experiments, we varied the deposition time and the oxygen pressure in the sample chamber. As a result, optimal conditions were found for encapsulant film growth on the phosphor powder, which considerably improved the service stability of the emission of electroluminescent light sources. After service aging, the brightness of a magnesium oxide-encapsulated phosphor sample was 80% higher than that of the uncoated sample.

Effect of plasmochemical modification on electro-optical and surface properties of zinc sulfide electroluminescent phosphors

Method for improving the brightness of photo- and electroluminescence from ZnS:Cu and ZnS:Cu, Al phosphors by their treatment in a low-temperature gas-discharge plasma was developed. The relationship between the luminescence brightness and spectra and surface properties of the phosphors was studied. The mechanism of processes that occur on the surface and in the bulk of phosphor particles during their bombardment with plasma ions was determined.

Effect of the Cu content and ZnS treatment on the characteristics of synthesized ZnS:(Cu, Cl) electroluminescent phosphors

The effect of the pretreatment of ZnS via different methods on the characteristics of synthesized ZnS:(Cu, Cl) electroluminescent phosphors with varying concentrations of the activator dopant (Cu) is studied. As a result of the pretreatment of ZnS with accelerated electrons and in nitrogen plasma, an increase in the emission brightness of the synthesized phosphor and a shift of the luminescence spectrum to longer wavelengths are observed. These effects are attributed with increase in content of the activator in the phosphor matrix because of the formation of extra defects in the ZnS structure during treatment. In the case of shockwave treatment of ZnS, the generation of defects is not compensated by heat treatment during synthesis of the phosphor, and a positive enhanced-brightness effect is not attained.

Local compositional environment of Er in ZnS:ErF3 thin film electroluminescent phosphors

ZnS:Er thin film electroluminescent phosphors have been shown to exhibit a marked maximum in the near infrared emission (NIR) after a 425 °C post-deposition anneal with a very narrow temperature window of ±25 °C for optimal NIR emission. Extended X-ray absorption fine structure (EXAFS) spectroscopy has been obtained from both the Zn and Er edges in order to examine the local structure of the host and dopant in this NIR phosphor material. Interestingly, the addition of only ∼0.5 mol. % of Er as ErF3 into the host is found to reduce the Zn–S bond length of one of the two nearest Zn–S shells by 0.6 Å relative to high-quality, atomic layer epitaxy (ALE) grown, pure ZnS. The coordination number of this shorter Zn–S bond increases after the optimal 425 °C anneal. Longer range fits indicate a highly disordered structure, overall, consistent with earlier TEM results. Erbium-L3 EXAFS data from the second and third shells show increasing crystallinity with increasing annealing temperature in the vicinity of the Er dopant. Data from the first shell cannot be fit with S atoms, but are fit equally well with either O or F. Comparison with earlier analyses indicates that the Er is most likely surrounded by F in the first shell. Based on these data and previous studies, we develop a model in which the Er dopant is present as an Er:Fx complex with associated S vacancies, which may include one sulfur atom remaining in the Er nearest shell. Upon annealing, there is a reduction in the F present and a rearrangement of the crystal structure in the vicinity of the Er atom. Optimum annealing conditions occur when optimal crystalline environment is achieved prior to the loss of too much F from the Er:Fx complex.

A model of active acid-base surface sites for zinc sulfide electroluminescent phosphors

Results of studies into surface properties of ZnS: Cu,Al and ZnS: Cu electroluminescent phosphors by the indicator method were summarized. The surface and electrooptical properties of these phosphors were examined in relation to the reaction batch composition and synthesis atmosphere, as well as to heat-treatment and electron-beam-induced modification regimes. On this basis, the structure of the surface active sites having different acid powers was established, and a surface model for zinc sulfide electroluminescent phosphors was proposed.

Crystal structure of quenched and in-field electroluminescent phosphors

Electroluminescent zinc sulfide doped with copper and chloride (ZnS:Cu, Cl) powder was heated to 400°C and rapidly quenched to room temperature. Comparison between the quenched and non-quenched phosphors using synchrotron radiation X-ray powder diffraction (XRPD) (λ = 0.828692 Å) and X-ray absorption spectroscopy (XAS) was made. XRPD shows that the expected highly faulted structure is observed with excellent resolution out to 150° 2θ (or to (12 2 2) of the sphalerite phase). The quenched sample compared to the unheated sample shows a large change in peak ratios between 46.7° and 46.9°, which is thought to correspond to the wurtzite (0 0 6), (0 3 2) and sphalerite (3 3 3)/(5 1 1) peaks. Hence, a large proportion of this sphalerite diffraction is lost from the material upon rapid quenching, but not when the material is allowed to cool slowly. The Zn K-edge XAS data indicate that the crystalline structures are indistinguishable using this technique, but do give an indication that the electronic structure has altered due to changing intensity of the white line. It is noted that the blue electroluminescence (EL) emission bands are lost upon quenching: however, a large amount of total EL emission intensity is also removed, which is consistent with our findings. We report the XRPD of a working alternating-current electroluminescence device in the synchrotron X-ray beam, which exhibits a new diffraction pattern when the device is powered in an AC field even though the phosphor is fixed in the binder. Significantly, only a few crystals are required to yield the diffraction data because of the high flux X-ray source. These in panel data show multiple sharp diffraction lines spread out under the region, where capillary data show broad diffraction intensity indicating that the phosphor powder is comprised of unique crystals, each having different structures.

10.1007/s11454-008-1013-6

The intensity of electroluminescence from an electroluminescent phosphor (electrophosphor) excited by unipolar voltage pulses with a linear front is studied. Based on experimental data, an expression for the free carrier emission rate in a planar electroluminescent capacitor with the polarization mechanism of luminescence is derived.

An Amorphous Indium–Gallium–Zinc–Oxide Active Matrix Electroluminescent Pixel

In this study, an active matrix pixel was fabricated and characterized using indium gallium zinc oxide (IGZO) thin-film transistors and a novel electroluminescent (EL) Eu:IGZO thin-film phosphor. The results show that even large and unoptimized IGZO devices are capable of modulating at the frequencies necessary for modern display technology. Furthermore, we demonstrate a rare-earth doped amorphous-oxide semiconductor (AOS) EL phosphor that can be modulated via a TFT.

P‐88: Effect of ZnS Treatment by Plasma on Properties of Derived Phosphors

AbstractInfluence of some parameters of plasma treatment of initial ZnS powder precursor on properties of derived phosphors has been investigated. for this we processed ZnS powder precursor with different parameters of plasma treatment: gases, different times and electric potentials. Electroluminescent phosphors were then synthesized using treated ZnS and EL devices were fabricated. Plasma treatment increased EL and PL brightness and also increased intensity of green band in emission spectra comparing to blue one.

Chitosan Clad Manganese Doped Zing Sulphide Nanocrystallites for Biolabeling

The synthesis of fluorescent nanocrystals is receiving a lot of attention for potential application in biological labeling as well as phosphors for field emission devices. Zinc sulphide doped with manganese (ZnS:Mn2+) is one of the most efficient electroluminescent phosphor displaying a wide emission band centred around 590 nm resulting from the intra-ionic transition in Mn2+ ions. We report a unique synthesis of zinc sulphide nanoparticles doped with manganese using a biocompatible passivating agent ‘chitosan’, with bright luminescence peaking at 590 nm. This high luminescence efficiency of the synthesized nanocrystals are ideal for quantum dot based bio-labeling applications. Synthesis of the nanoparticles was carried out by precipitation reaction in aqueous media of zinc acetate and sodium sulphide where manganese acetate was added as the dopant. The obtained nanoparticles were around 4 to 6 nm in size and were found to be stable for months of shelf life. The photoluminescence intensity did not degrade when the colloid was heated up to 65 oC for prolonged periods.

Preparation of the ZnS-type Electroluminescent Phosphor Used in Flat Panel Display Field

ZnS electroluminescent phosphors were prepared by high temperature (1100℃) solid state reaction,subsequently milling for some time (t=0-180min) and the final low temperature annealing process (750℃).The as-synthesized phosphors were characterized by X-ray powder diffraction,UV-Vis diffuse reflectance spectra,scanning electron microscope and photoluminescence spectra.Electrolu- minescence performance was investigated on the screen-printing electroluminescent lamp at 100V and 400Hz.Increased milling time leads to intensity reductions and width increases of some diffraction peaks, and results in slight red-shifts of the absorption edges.Photoluminescence brightness declines about 58% after milling for 180 min while electroluminescence brightness increases from 14.39cd/m~2(t=0min) to the peak value 90.13cd/m~2(t=160min).The changes of photoluminescence and electroluminescence performances originate from the defects in the microstructure induced by milling.

A simple procedure for electroluminescent phosphor assessment

A simple assessment procedure is described which facilitates optimal selection of an electroluminescent phosphor based on the measurement of two optically deduced energies—absorption and emission. These two energies are used as input for an appraisal analysis based on a classical configuration-coordinate diagram model of the phosphor. A phosphor performance figure-of-merit is proposed as a consequence of the formulation of this assessment procedure. This procedure is then used to rationalize the relative performance of five electroluminescent phosphors (ZnS:Mn, BaAl 2 S 4 :Eu, SrS:Ce, SrGa 2 S 4 :Ce, CaGa 2 S 4 :Ce). Additionally, two cathodoluminescent phosphors (ZnS:Ag and ZnS:Cu) are appraised using this methodology, suggesting that this procedure may be of some utility in the evaluation of other types of phosphors.