Luminescent Device Applications Research Articles

Controllable synthesis, characterization of ZnS nanostructured spheres

ZnS nanostructured spheres have been synthesized successfully without the assisted of surfactant, templates or capping agent via a facile hydrothermal method. Structural, morphological and optical characterization was fully performed. On the basis of characterization results, it was founded that the concentration of sulfur sources, hydrothermal reaction time and reaction temperature had an important effect on the formation of ZnS nanostructured spheres. The reason that reaction parameters are how to affect the formation of nanostructured spheres was investigated and discussed in detail. The formation mechanism of nanostructured spheres was innovatively proposed based on experimental results. The strong green PL emission of such structures would provide a potential application in novel luminescent devices. In addition, the route for the synthesis of ZnS nanostructures will be a promising way in the industrial application.

Synthesis of a PPV‐fluorene derivative: Applications in luminescent devices

ABSTRACTSynthesis of a polyfluorene/poly(p‐phenylene vinylene) derivative, the Poly [(9,9′‐di‐hexylfluorenediylvinylene‐alt‐1,4‐phenylenevinylene)‐co‐((9,9′‐(3‐t‐butylpropanoate) fluorene‐1,4‐phenylene)] (LaPPS 42) was performed following Wittig and Suzuki routes. Polyfluorenes and derivatives have been used in electroluminescent devices, and the synthesis described here has the advantage in pave the way to get distinct structures having different emission spectra. An extensive study of its electrochemical, thermomechanical, optical, and structural properties was carried out, as well as its application in electroluminescent devices. Polymer light‐emitting diodes (PLEDs) and polymer light‐emitting electrochemical cells (PLECs) were built using LaPPS 42 as active layer, and their electric and optical characterizations confirm they have a potential as active element in electroluminescent devices. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42579.

Energy transfer based photoluminescence properties of (Sm3+ + Eu3+):PEO + PVP polymer films for Red luminescent display device applications

Eu3+:PEO+PVP, Sm3+:PEO+PVP and co-doped Sm3++Eu3+:PEO+PVP polymer films have successfully been synthesized by solution casting method. For these polymer films, their XRD, FTIR and RAMAN spectral profiles were studied systematically. Both absorption and photoluminescence spectra have been assessed by evaluating their optical properties. The Sm3+:PEO+PVP and Eu3+:PEO+PVP polymer film has displayed a reddish-orange and red emissions at 596nm and 619nm respectively under an UV lamp. A reddish-orange emission was found for Sm3+:PEO+PVP polymer film at 596nm (4G5/2→6H7/2) and its lifetime has also been evaluated suitably. Red emission at 619nm (4G5/2→6H7/2) of Eu3+ has been identified for Eu3+:PEO+PVP polymer film and its lifetime are also evaluated. The photoluminescence efficiency of Eu3+ ion has been enhanced due to the addition of Sm3+ by means of an energy transfer process. The energy transfer mechanism, from Sm3+ to Eu3+ has been clearly established. At 0.1wt% concentration of Sm3+ ions (sensitizer), the photoluminescence efficiency of the Eu3+ ion (activator) has been significantly enhanced in co-doped sample through energy transfer from Sm3+ to Eu3+ in the polymer matrix. The energy transfer process has been analyzed using lifetime decay dynamics. From the obtained results, these polymer materials could be proposed as potential Red luminescent optical materials.

Mn 掺杂ZnSe 量子点变温发光性质研究

Thermal stability of quantum dot( QD) luminescence is considered as an important factor for their applications in luminescent devices because of the Joule heat caused by inevitable current. The temperaturedependent photoluminescence( PL) properties of Mn-doped Zn Se( Mn∶ Zn Se) QDs with different shell thickness in the temperature range from 80 to 500 K were studied by steady-state and time-resolved PL spectra. It was found that the Mn∶ Zn Se QDs with thick shell( 6. 5 monolayers( MLs)) exhibited better PL thermal stability than the thin shell coated ones( 2. 6 MLs). Because almost no PL quenching occurred for thick shell-coated Mn-doped QDs from 80 to 400 K,their PL quantum yield( QY) could keep 60% even at 400 K. Moreover,based on the change in temperature-dependent PL intensities and lifetimes of Mn ∶ Zn Se QDs,the thermal quenching mechanism was proposed. Finally,the stability of Mn∶ Zn Se QDs with different shell thickness are discussed on the basis of heating-cooling cycling examination( 300-500-300 K). For Mn∶ Zn Se QDs with thick shell,the PL was nearly totally recovered after the cycling examination. Thus,Mn∶ Zn Se QDs are promising for applications in luminescent devices,where strong thermal effect is inevitable.

Intercalation of lanthanide cations to a layer-like metal-organic framework for color tunable white light emission.

One gallium carboxylate of MOF (Ga2(OH)4(C9O6H4) or MIL-124) has been synthesized by a facile solvothermal approach, and the luminescence was tuned by encapsulating lanthanide(iii)(Ln(3+)) cations into the channels through the active-COOH group in MIL-124 post-synthesis. PXRD, TEM, FTIR, and TGA were performed to determine the structure and thermal stability of the obtained products. The photophysical properties of these Ln(3+) incorporated products are studied in detail, whose luminescent color can be tuned by controlling the composition of different Ln(3+) cations in MOF. Furthermore, with careful adjustment of the excitation wavelength and concentration of the Ln(3+) cations, the color of the luminescence can be modulated, and dichromatic (MIL-124@Eu(3+)) and trichromatic (MIL-124@Eu(3+)/Tb(3+)) white-light-emission can indeed be achieved. One of the optimized chromaticity coordinates in white-light-emission is (0.3693, 0.3362) which is very close to the value for ideal white-light (0.333, 0.333). The versatile luminescence, good thermal stability, and compatibility with aqueous conditions reveal that these materials based on MOF may have some potential applications in luminescent devices for display or lighting.

Dy3+-doped tellurite based tungsten-zirconium glasses: Spectroscopic study

Tellurite based tungsten zirconium glasses-doped with trivalent dysprosium (Dy3+) ions (TWZDy) have been prepared by conventional melt-quenching technique and characterized through thermal, structural and spectroscopic measurements. XRD pattern of the glass confirms its amorphous nature. The functional groups of the TeO3 and TeO4 units along with WO− and ZrO vibrations have been identified from Fourier transform infrared spectrum. The energy level analysis has been carried out by using the parametric free-ion Hamiltonian model. Judd–Ofelt theory has been used to explore the spectral intensities of Dy3+ ions in the present glass system. From the emission spectra, the emission intensities increases from 0.05 to 1.0mol% of Dy3+ ion and then decreases for higher concentrations due to energy transfer between Dy3+ ions. The higher value of peak stimulated emission cross-section (40.46×10−22cm2), noticed for 4F9/2→6H13/2 transition, is comparable with other reported Dy3+ systems. The TWZDy glasses emit intense yellowish-white color (x=0.32; y=0.44) which is nearer to standard white light zone. The decay curves exhibit single exponential nature at lower concentrations (⩽0.1mol%) and turns into non-exponential (⩾0.5mol%) due to energy transfer processes. In order to unravel the energy transfer process the non-exponential decay curves have been fitted to Inokuti–Hirayama (IH) model with S=6. The analyses of the results indicate that the present TWZDy glasses are suitable for luminescent display device applications as well as for white light generation.

A study of the nano-structured aggregated tin oxides (SnO2/SnO) and their structural and photoluminescence properties by a hydrothermal method

Aggregated tin oxide (SnO2/SnO) nanostructures were produced in the presence of double tin salts (SnCl4·5H2O, SnCl2·2H2O), metal hydroxyl precursors (caustic soda and ammonia), poly(oxy)ethylene glycol-400 and water as a solvent, by a hydrothermal method. The crystal structure, functional groups, morphology, and photoluminescence properties of the SnO2/SnO nanostructures are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Energy dispersive X-ray (EDX), scanning electron microscopy (SEM) and Photoluminescence (PL) analysis. The XRD and SEM studies indicated the formation of a mixed phase of SnO2/SnO with a nanocrystalline nature. The FTIR and EDX analyses also confirmed the formation of the Sn–O bond. The PL emission spectrum of the SnO2/SnO nanostructures was observed in the visible region (blue, green, yellow and red emission peaks), due to the oxygen vacancies or other defects, and it could be used for luminescent device applications.

Strong red emission and electrical properties of highly c-axis oriented Eu3+-doped bismuth vanadate ferroelectric thin films

Highly c-axis oriented Bi2−xEuxVO5.5 (x = 0, 0.05, 0.10, 0.15, and 0.20) thin films were prepared on Pt(111)/Ti/SiO2/Si and fused silica substrates by using chemical solution deposition method, and characterized by X-ray diffraction, scanning electron microscopy, and optical and electrical measurements. Under 356 nm UV irradiation, a bright red photoluminescence can be observed in the thin films with x = 0.10, 0.15, and 0.20. The emission spectra included two strong peaks which originated from 5D0 → 7F1 (595 nm) and 5D0 → 7F2 (619 nm) transitions of Eu3+ ions. With increasing Eu3+-doping content x, the dielectric dispersion weakened, and dielectric loss decreased. Eu3+ doping can also decrease the leakage current of the thin films. These results demonstrate that Bi2−xEuxVO5.5 thin films are a kind of multifunctional material with potential applications in luminescent ferroelectric devices.

Optical Properties of Plate-Shaped ZnO Nanocrystals Grown by a Facile and Environmentally Friendly Molten Salt Method

Plate-shaped ZnO nanocrystals are prepared by a facile and environmentally friendly molten salt method, in which Zn5(CO3)2(OH)6 nanorods are first synthesized via a facile one-step, solid-state reaction route at room temperature and then decomposed in NaCl flux. Photoluminescence property demonstrates that the as-prepared plate-shaped ZnO nanocrystals exhibit a strong blue emission centered at about 483 nm. Raman scattering spectrum reveals that the as-prepared plate-shaped ZnO nanocrystals have the oxygen deficiency, which can be confirmed by the appearance of oxygen-deficiency-related vibrational mode at 583 cm−1 in the Raman spectrum. The oxygen deficiency existing in the plate-shaped ZnO nanocrystals results in the formation of the oxygen vacancy, which is most likely responsible for the strong blue emission of the plate-shaped ZnO nanocrystals. These new plate-shaped ZnO nanocrystals with strong blue emission are expected to show considerable potential applications in luminescence, lasing and optoelectronic devices.

Synthesis and Electroluminescent Properties of OLED Green Dopants Based on BODIPY Derivatives

Organic light-emitting diodes (OLEDs) based on the small organic molecules have gained remarkable attention for display and solid-state lighting applications over the last few years due to their well-defined molecular structures, facile syntheses and modifications, and specific structure-property correlations. One approach that has been used to improve the efficiency of the OLED devices in term of brightness and stability is the introducing of the highly fluorescent organic guest dopants into the host materials to obtain the full color display. Therefore, there is still a need for the development of new dopants with good color purity, stability and high efficiency. Difluoroboradiaza-s-indacene (BODIPY) represents an outstanding class of fluorophore with high quantum yield, large molar absorption coefficient, high chemical, thermal and photophysical stability. The development of new BODIPY derivatives has become a booming of research due to their potential applications in luminescent devices, chemical sensors, biological labeling, and photovoltaic cells. Major efforts have been devoted to obtain the welldesigned BODIPY structures by modifying of the pyrrole core, fusing some aromatic rings to the BODIPY core, and replacing the 8-carbon atom with a nitrogen atom to form aza-BODIPY. The incorporation of boron element into the π-conjugated framework may lead to the appearance of unique electronic and photophysical properties. Recently, we have successfully explored some green dopants based on arylamine 2,3-disubstituted bithiophene derivatives for OLEDs. In the course of our ongoing studies, herein we wish to report the novel green dopants based on BODIPY and two different arylamine moieties with good overall performance in the multilayer device (Figure 1). In the design of the target molecules 5a–b (Figure 1), the outstanding fluorescent BODIPY core was fused with different arylamine moieties which were expected to enhance the light emitting efficiency through the extension of the

Effect of Thermal Annealing and Swift Heavy Ion Irradiation on the Optical Properties of Indium Oxide Thin Films

Indium oxide thin films were fabricated by electron beam evaporation method. Two different methods viz. thermal and ion irradiation were employed to tailor the structural and optical properties. One set of samples was annealed at various temperatures (300, 400, 500 and 600°C) to obtain the crystallinity. Another set of samples (as-deposited and 600°C annealed film) was irradiated with 120 MeV Ag ions, at different ion fluences (i.e.1 × 1011, 1 × 1012 and 1 × 1013 ions-cm−2). The structural changes were monitored by X-ray diffraction and optical properties were investigated by using UV-visible spectroscopy and photoluminescence spectroscopy. Thermal annealing of as-deposited films leads to the improvement in crystalline indium oxide phase, whereas ion irradiation resulted in the formation of crystalline indium phase. Transparency of as-deposited films improves upon thermal annealing (from 70% to 89%) whereas, ion- irradiation of crystalline indium oxide film leads to a reduction in transparency (89% to 60%) at higher fluence. Moreover, irradiation of crystalline indium oxide film gives an emergence of a broad and highly intense PL emission peak in the visible region (∼680 nm). Our results indicate that a desired combination of properties can be achieved by varying the ion fluence for the further possible applications in luminescence devices.

High-Temperature Luminescence Quenching of Colloidal Quantum Dots

Thermal quenching of quantum dot (QD) luminescence is important for application in luminescent devices. Systematic studies of the quenching behavior above 300 K are, however, lacking. Here, high-temperature (300-500 K) luminescence studies are reported for highly efficient CdSe core-shell quantum dots (QDs), aimed at obtaining insight into temperature quenching of QD emission. Through thermal cycling (yoyo) experiments for QDs in polymer matrices, reversible and irreversible luminescence quenching processes can be distinguished. For a variety of core-shell systems, reversible quenching is observed in a similar temperature range, between 100 and 180 °C. The irreversible quenching behavior varies between different systems. Mechanisms for thermal quenching are discussed.

Cooperatively exfoliated fluorinated graphene with full-color emission

We report a novel and effective method to prepare fluorinated graphene sheets (FGS) by the cooperative exfoliation of graphite fluoride using cetyl-trimethyl-ammonium bromide and dopamine. This facile, scalable preparation route results in wide (about 2 μm in width), long (at least 3 μm in length) and ultrathin (1–2 layers) FGS with uniform morphology. The chemical composition of FGS was characterized by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The obtained FGS exhibits full-color emission when excited by near ultraviolet (NUV) rays, suggesting its potential applications in luminescence devices, such as NUV-pumped FGS-based flexible light-emitting diodes.

Synthesis and Characterization of Electrospun Poly(ethylene oxide)/Europium-Doped Yttrium Orthovanadate (PEO/YVO4:Eu3+) Hybrid Nanofibers

Europium-doped yttrium orthovanadate/polyethylene oxide nanofibers were fabricated by firstly, synthesizing crystalline YVO4:Eu3+ nanoparticles using an aqueous precipitation method followed by electrospinning of PEO/YVO4:Eu3+ polymer composites. X-ray diffraction patterns showed that the nanoparticles exhibited well-defined peaks that were indexed as the tetragonal phase of YVO4. No additional peaks of other phases were observed indicating that Eu3+ ions were effectively built into the YVO4 host lattice. The photoluminescence spectra for the nanofibers showed peaks at 593, 615, 650, and 698 nm which was ascribed to the 5D0− 7F1, 5D0− 7F2, 5D0− 7F3 and 5D0− 7F4 transitions of Eu3+. Due to an efficient energy transfer from vanadate groups to Eu3+, the composite nanofibers showed a strong red emission under ultraviolet excitation characteristic of the red luminescence of the europium ion. The results demonstrate that this synthetic approach could prove to be viable for the fabrication of rare earth/polymer composite nanofibers intended for luminescent device applications.

Structural, electrical and optical properties of Dy doped ZnO thin films grown by buffer assisted pulsed laser deposition

Abstract Transparent conductive dysprosium doped ZnO (Dy:ZnO) thin films with preferential orientation in the (0 0 0 2) direction were deposited on (0 0 0 1) sapphire substrate by buffer assisted pulsed laser deposition. The experimental results show that the resistivity of Dy:ZnO thin films decreased to a minimum value of ∼7.6×10−4 Ω cm with increasing Dy concentration up to ∼0.45 at%, then increased with the further increase of Dy concentration. On the contrary, the band gap and carrier concentration of Dy:ZnO thin films initially increased, then decreased with increase of Dy concentration. The blue shift of band gap of Dy:ZnO thin films with increasing carrier concentration was attributed to the competing effects of Burstein-Moss shift and band gap narrowing. A bright room temperature photoluminescence observed at ∼575 nm in all the Dy:ZnO thin films, with maximum intensity at ∼0.45 at% of Dy doping, was attributed to be due to intra-band transitions of Dy3+ in ZnO. Near band edge photoluminescence of ZnO was observed at ∼380 nm with photoluminescence intensity decreasing with increase of Dy concentration. Such Dy:ZnO thin films are found to be suitable candidate for luminescent device applications.

Enhanced photoluminescence and the self-assembled fibrillar nanostructure of 5-(cholesteryloxy)methyl-8-hydroxyquinoline lithium in a gel state

Soluble 5-(cholesteryloxy)methyl-8-hydroxyquinoline lithium(I) (LiChQ) was synthesized through the modification of 8-hydroxyquinoline lithium (LiQ) with cholesterol, and showed about 3 times more enhanced luminescence than pristine LiQ. When increasing the concentration of LiChQ up to 1 wt% in non-protic solvents, nanoscale fibers of 30–100 nm diameter were formed through self-assembly in a super-gel state. There was a red shift in the absorption of the gel in comparison to the solution, which indicates that LiChQ tends to form a J-aggregate in the gel state. We also investigated the gelation process of LiChQ using the Lippert–Mataga equation. We suggest that LiChQ has potential applications in luminescent devices and/or as a template for nanostructured optoelectronic materials.

Optical Properties of CdS–PVA Nanocomposites

Semiconductor–polymer nanocomposites, with good control over the nanoparticle size and their dispersion within the polymer matrix, can have applications in many optical and luminescent display devices. Cadmium sulphide (CdS) is the most popular semiconductor nanoparticle exhibiting size dependent properties due to its large exciton binding energy and its suitability for large scale production. The nanoparticles need to be passivated against aggregation with suitable capping agents, without sacrificing the desirable properties like transparency and flexibility of the polymer. Cadmium sulphide nanoparticles capped with polyvinyl pyrrolidone (PVP) are synthesized using cadmium nitrate (Cd(NO3)2) and hydrogen sulphide (H2S) as Cd2+ and S2– sources, respectively. CdS particles with sizes in the range of 5–6 nm are prepared in methanol and the solvent is removed using a rotary evaporator. CdS powder is dispersed in polyvinyl alcohol (PVA) solution with dimethyl formamide (DMF) as solvent to get (PVP–CdS)–PVA nanocomposite film of about 0.2 mm thickness. This has been characterized by powder X-ray diffraction (XRD), optical absorption studies, transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and photoluminescence (PL). Particle size does not change due to incorporation in the polymer matrix and the polymer retains its transparency and flexibility. The nanocomposite shows good photoluminescence property with stronger band edge emission than defect related emission. The latter could be quenched completely by optimizing the PVP content. Irradiation of the nanocomposite with 8 MeV electrons at a dose of 100 kGy could effectively quench the defect related emission.

Synthesis and luminescence of pure and Eu 3+-activated Aurivillius-type Bi 3TiNbO 9 nanophosphors

Undoped and Eu 3+-activated Bi 3TiNbO 9 (BTNO) nanophosphors have been successfully synthesized by sol–gel combustion method. The effects of thermal annealing on the phase structure and crystallinity, morphology and UV–vis absorption of BTNO particles were investigated. Photoluminescence (PL) properties show that a broad blue emission was detected for BTNO nanoparticles, and the characteristic Eu 3+ ion 5D 0 → 7F J ( J = 1, 2, 3, 4) transitions were observed for the doped samples. Further investigation illuminates that the Eu 3+ ions substituted for Bi 3+ ions at A site in the pseudo-perovskite layers. It can be confirmed from high bright fluorescence image and short decay time that the novel orange-red phosphor has the potential applications in luminescence devices.

2D Self-Bundled CdS Nanorods with Micrometer Dimension in the Absence of an External Directing Process

In the absence of an external direction-controlling process, exclusive self-bundled arrays of CdS nanorods are formed using a facile solution-based method involving trioctylphosphine (TOP) and tetradecylphosphonic acids (TDPA) as cosurfactants. CdS self-bundled arrays with an area of as large as 2.0 microm(2) could be obtained. A detailed mechanistic investigation leads us to conclude that the matching in nanorod concentration, intrinsic properties of CdS, and the hydrocarbon chains of the surfactants between adjacent CdS rods play key roles in the self-assembly. In sharp contrast to the defect dominant emission in solutions, the self-bundled CdS nanorods exhibit optical emission nearly free from the defect-states, demonstrating their potential for applications in luminescence and photovoltaic devices.

The Counter Anionic Size Effects on Electrochemical, Morphological, and Luminescence Properties of Electrochemically Deposited Luminescent Films

Luminescent films electrodeposited (ED) on indium tin oxide glass are considered for application in low-cost luminescent devices. During ED processes, the anions play an important role in the quality of resultant ED films. Three species of supporting electrolytes TBA-X (, , , and ) with different size of anions were used for the preparation of ED films from a branched carbazyl luminescent precursor TCPC. Increasing the size of anions resulted in an increase of growth rate and improved the morphology of ED films. The ED film prepared using as supporting electrolyte showed strong fluorescence with efficiency of , which was significantly higher than that of ED films from the smaller anions and . By utilizing the ED films as emitting layer, the light-emitting device also showed improved performance with increasing size of anions in the electrolytes. The origin of observed counter anionic size effects on electrochemical, morphological, and luminescent properties of ED films can be attributed to the difference in interaction between the carbazyl cation and anions, which induced an easier (i.e., for the larger size ions) or difficult (i.e., for the smaller size ions) dedoping process.