Blue-green Light Emission Research Articles

Fabrication of lead titanate single crystalline nanowires by hydrothermal method and their characterization

Single crystalline nanowires of lead titanate (PbTiO3) were fabricated by hydrothermal method at 200°C using lead acetate and n-tetrabutyl titanate as starting materials, where sodium hydroxide was served as a mineralizer. Crystalline phases, microstructure and optical properties of PbTiO3 nanowires were investigated. The PbTiO3 nanowires were uniform and continuous along the long axis, and were composed of single crystalline PbTiO3 with a tetragonal perovskite structure. The diameter of a single nanowire was around 12 nm and the length reached up to 3 μm. The chemical composition of the samples and the valence states of elements were determined by X-ray photoelectron spectroscopy (XPS). The ultraviolet/visible absorption spectroscopic investigation suggested that the absorption edge of optical transition of the first excitonic state occurred at around 320 nm. A blue-green light emission peaking at about 471 nm (2.63 eV) is observed at room temperature, and the intensity of this emission increased with increasing excitation wavelength. Oxygen vacancies are responsible for the light emission of PbTiO3 nanowires.

γ - Ga 2 O 3 quantum dots with visible blue-green light emission property

Visible blue-green light emission metastable γ-Ga2O3 quantum dots were prepared, and the light emission is clearly visible to the naked eyes. The UV-visible spectra present a blueshift phenomenon of the absorption edge as the particle sizes decrease; the fitted result of UV-visible data by Tauc function shows that the as-prepared γ-Ga2O3 is a wide-band-gap semiconductor with a direct band gap structure. The photoluminescence spectra show the evidence of quantum confinement and a blueshift when the crystal sizes decrease.

Synthesis and optical properties of aluminum and zinc quinolates through styryl subsituent in 2-position

4-Methyl(methoxy or chloro)benzaldehyde reacted with 2-methyl-8-quinolinol to afford the corresponding substituted 2-styryl-8-quinolinol. The latter was used as chelating ligand to prepare aluminum and zinc complexes. The spectroscopic, thermal, thermomechanical and optical properties of these complexes were investigated. The thermal stability of the complexes was much higher than the reference complexes AlQ 3 and ZnQ 2. The char yield at 800 °C in N 2 for typical complexes of Al and Zn was 49–64% whereas that for the reference complexes was 13–31%. The processability of the complexes was improved since they were soluble in common organic solvents such as THF, chloroform and acetonitrile. Solutions of complexes in THF emitted blue-green light with photoluminescence (PL) maximum at 513–576 nm that is considerably red-shifted relative to AlQ 3 (514 nm) and ZnQ 2 (535 nm). In addition, the PL maximum in THF of the synthesized Zn complexes was red-shifted as compared to the corresponding Al complexes. The nature of the styryl substituent (methyl, methoxy or chloro) of the chelating ligand influenced also the location of the PL maximum.

Low-potential electrochemical polymerization of fluorene and its alkyl-polymer precursor

High quality polymer films can be easily produced by low-potential anodic oxidation of fluorene and its alkyl-polymer precursor through 9,9 position (9,9-dibromohexylfluorene, 9-(6-bromohexyl)fluorene, poly(fluorene-9,9-diyl-alt-alkan-1,6-diyl); Scheme 1) in boron trifluoride diethyl etherate (BFEE) or mixed electrolytes of BFEE + CHCl 3. As-formed polymer films showed good redox behavior and were characterized by UV–vis, infrared, fluorescence spectroscopy and thermal analysis. Fluorescence spectral studies both in solution and in solid-state revealed that as-formed polymer films were good blue-green light emitters with strong emissions at about 420 and 560 nm. The substitutions of alkyl group and alkyl-polymer fluorene precursors were helpful for the red shift of emission wavelength of as-formed polyfluorenes.

SYNTHESIS AND ELECTROLUMINESCENT PROPERTY OF ALUMINUM AND α-PYRIDOIN COMPLEX

A novel light-emitting aluminum complex (PAl) containing the dihydroxy derivative of trans-1,2-dipyridylethene, α-pyridoin, was synthesized and its electroluminescent (EL) properties characterized. The chemical structure of the complex was elucidated by FT-IR, UV-Vis and XPS. The complex showed thermal stability up to 350°C under nitrogen flow by TGA. The photoluminescence (PL) was measured from PAl cast film on quartz plate. Electroluminescent device having the structure of ITO/TPD/PAl/Al was fabricated by vacuum deposition, where N,N-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) was used as a hole transporting layer. The device emitted blue-green light of around 480 nm. The maximum luminance of 38 cd/m2 and current density of 0.09 mA/cm2 were observed at 34 V.

White Organic Light-Emitting Devices Based on2-(2-Hydroxyphenyl) Benzothiazole and Its Chelate Metal Complex

We present three kinds of organic light-emitting devices (OLED)fabricated to achieve the emission of bright and pure white light.Device A, with a double-layered structure using 2-(2-hydroxyphenyl)benzothiazole (HBT) and poly (N-vinylcarbazole) (PVK) as the emittinglayer (EML) and the hole transport layer (HTL) respectively, couldrealize the blue-green light emission. Bis-(2-(2-hydroxyphenyl)benzothiazole)zinc (Zn(BTZ)2), synthesized with zinc acetatedihydrate and HBT to form a complex, is used as main EMLs in a similarstructure to fabricate devices B and C. Bright and pure white lightemissions can be obtained from device C which was fabricated with agreen-white emitting host Zn(BTZ)2 and red dopant5,6,11,12-tetraphenylnaphthacene (rubrene). The maximum quantumefficiency of device C could reach 0.63%, and the correspondingbrightness and CIE coordinates were 4000 cd/m2 and (x = 0.341, y = 0.334) at the driving voltage of 20 V.

Realization of one-chip-two-wavelength light sources

We proposed a vertically integrated one-chip-two-wavelength light source which consists of a separate confinement single-quantum-well (SCH-SQW) ZnCdSe/ZnSe/ZnMgBeSe heterostructure for blue–green light emitters grown on SCH-MQW InGaP/InGaAlP for red light-emitting devices. We investigated, firstly, the effect of a thin low-temperature-grown ZnSe buffer layers (LT-ZnSe) in improving ZnSe crystallinity by inserting it between the high-temperature-grown ZnSe epilayer and the GaAs substrate, secondly, the growth optimization of LT-ZnSe on tilted GaAs (0 0 1) substrate, and lastly, the molecular beam epitaxy growth and characterization of ZnCdSe/ZnSe/ZnMgBeSe quantum well structures on metal organic chemical vapor deposition (MOCVD) grown III–V red light emitters. Optically pumped lasing is achieved from II–VI and III–V laser structures on one chip at room temperature. The present results clearly show the feasibility of epitaxial integration of II–VI and III–V laser structures.

Corneal fluorescence in relation to genetic and environmental factors: a twin study.

Corneal fluorescence is believed to be caused by advanced glycation end products formed by non-enzymatic glycation on corneal proteins. The purpose of the present twin study was to examine whether the process is related to genetic or environmental factors. Corneal fluorescence was measured in 59 monozygotic and 54 dizygotic twin pairs. The influences of genetic and environmental factors were estimated using structural equation modelling. Interindividual variation in corneal fluorescence was attributable to environmental factors, whereas the effect of genetic factors was of little or no significance. Corneal fluorescence correlated significantly with smoking habits (r = 0.38) and the 2-hour oral glucose tolerance test response (r = 0.27), and increased with age (p < 0.0001). Fluorophore accumulation in the cornea was attributable to age and environmental effects, of which smoking was the most conspicuous identifiable factor, although glucose was also of relevance. However, the greater part of interindividual variation in corneal fluorescence remains unexplained.

A novel synthesis of indium phosphide nanoparticles

Nanosized indium phosphide has been prepared by direct reaction of sodium phosphide and anhydrous indium trichloride in N, N′-dimethylformamide (DMF) at a temperature between 120 and 160 °C under argon atmosphere. This is the first report on the synthesis of indium phosphide at normal pressure by the use of sodium phosphide. The product was characterized by solution UV–visible measurement, photoluminescence (PL) study and powder X-ray diffraction (XRD). Solution absorption measurements indicate a blue shift of about 400 nm when compared with bulk indium phosphide, and an air-stable blue-green light emission has been observed with λ (em.) at 462 and 550 nm, depending upon the reaction conditions. Powder X-ray measurements showed a broad pattern that match well with the amorphous nature of indium phosphide.

The distribution and possible origin of blue—green fluorescence in control and stressed barley leaves

Apart from red (chlorophyll a) fluorescence, ultraviolet (UV) excitation of plant leaves results in blue-green intrinsic light emission. In order to analyse the potentially modifying influence of stress on this blue-green fluorescence (BGF), and to determine its origin, the fluorescence was characterised by spectroscopy, and two and three dimensional microscopy in leaves of Hordeum vulgare L. under UV and drought stress. Leaves of wild-type and proanthocyanidin-free mutant barley were compared. In general, the BGF was enhanced by stress. The analysis of the distribution of BGF pointed to differences in response to the different stress conditions and served to indicate possible sources of the fluorescence. This study showed that (1) the selective enhancement of BGF by supplementary UV radiation (280-360 nm) in upper leaf tissues of wild-type but not in proanthocyanidin-free leaves, pointed to flavonoids as possible emitters; (2) drought-inducible BGF emission was found in cell walls and to a smaller extent in upper leaf tissue regardless of genotype, thus independent of impairment in flavonoid biosynthesis and (3) intracellular BGF, which co-localised with red chlorophyll fluorescence, was inducible in mesophyll cells of both genotypes by short-term application of high levels of UV radiation.

Electroluminescence properties of new multi-functional copolymers containing carbazole, naphthalimide and oxadiazole

We have prepared a new class of copolymers containing carbazole, 1,8-naphthalimide and 1,3,4-oxadiazole. Optical properties of the copolymers are studied in the UV-visible region. Thermogravimetric analysis and differential scanning calorimetry examined their thermal stability. The copolymers are soluble in common organic solvents, and emit blue-green light under the irradiation of UV light in their film states. For these copolymers, there is an intramolecular energy transfer from carbazole and 1,3,4-oxadiazole to 1,8-naphthalimide. Single-layer devices of indium tin oxide/copolymers/aluminum utilizing these copolymers as emissive materials were fabricated, that emitted blue-green light at 6–8 V under a forward bias.

Synthesis and characterization of a novel 1,4-naphthalene-based thiophene copolymers

A novel soluble 1,4-conjugated naphthalene-based thiophene copolymer was chemically synthesized and characterized. The copolymer demonstrates efficient blue–green light emission with a fluorescence quantum yield of up to 31% in solution. It has good solubility in most organic solvents and good thermal stability. Upon oxidation with I 2 or FeCl 3, conductivity of up to 10 −5 Ω −1 cm −1 for copolymer was observed.

Polymer light-emitting electrochemical cells with the block copolymers containing PEO segments

Polymer light-emitting electrochemical cells (LECs) were fabricated and characterized with three block copolymers containing PEO segments as the luminescent polymers. The block copolymers are composed of PPV segments with three phenylene vinylene units and PEO segments with three ethylene oxide units. Blue–green light-emission of the LECs was demonstrated with the onset voltage lower than 3 V and EL efficiency of 0.74 cd/A at 2.8 V. The response time of the LECs is approximately 5 s. The transient response and a.c. impedance data indicate that the operating mechanism of the LECs is an electrochemical doping model.

Amphiphilic phenylene-ethynylene polymers and oligomers for polarized electroluminescence

We investigate the electroluminescence of polymer and oligomer derivatives of p(phenyl-ethynylene) bearing amphiphilic side chains. The polymer and the heptamer show liquid crystalline properties, which are characterized by X-ray diffraction. A periodic structure is observed, which corresponds to a lamellar system with a layer spacing of about 3.8 nm. Two other diffuse bands correspond to a liquid-like order of the side chains and a weak interaction of the π–π interactions between phenyl rings. We have investigated the absorption and the photoluminescence (PL) properties of the polymer and the heptamer films prepared by the Langmuir–Blodgett (LB) and by spin-coating techniques. The polymer film shows an absorption peak at 408 nm with a shoulder at 436 nm; while the heptamer shows a small blue shift of the main peak at 382 nm and the shoulder at 415 nm. Based on the liquid crystalline properties, the two materials can be oriented by rubbing, giving rise to a good dichroic absorption spectrum. The ordering parameter at the peak absorption is better for the polymer than for the heptamer, OP=0.58 and 0.45, respectively. The PL of the two materials are observed at 539 and 516 nm, respectively. The PL yields, measured by the integration sphere method, gives a result of 0.23 and 0.20 emitted photon per absorbed photon respectively. A good dichroic photoemisson is also observed on the oriented rubbed films prepared by spin-coating. We demonstrate that the oligomer can be used in a blue-green light emission device by using the LB multilayer or by spin-coating techniques. We investigate the polarized electroluminescence in devices with the configuration ITO/film/LiF–Al. The oligomer (or the polymer) films are oriented by rubbing. A polarized emission parallel or perpendicular to the sliding direction is observed. The measured dichroism reaches a value of 8 at 531 nm for the heptamer.

Blue-green light-emission LECs based on block copolymers containing di(α-naphthalene vinylene)benzene chromophores and tri(ethylene oxide) spacers

The polymer light-emitting electrochemical cells (LECs) were fabricated and characterized with two novel block copolymers as the luminescent polymers. The block copolymers are composed of the rigid segments (chromophores), 1,4-di(α-2-naphthalene vinylene)benzene (DNVB) or 2,5-dimethyloxy-1,4-di(α-2-naphthalene vinylene)benzene (MDNVB) and the flexible segments (spacers), tri(ethylene oxide) (TEO). Efficient blue-green light emission of the LECs was demonstrated with onset voltage lower than 3 V and electroluminescence (EL) efficiency of ∼0.2 cd/A. The a.c. impedance data indicate that the operation mechanism of the LECs agrees with the electrochemical doping model.

Synthesis of π-Conjugated Poly(cyclodiborazane)s by Organometallic Polycondensation

Donor−acceptor type π-conjugated poly(cyclodiborazane)s were synthesized by organometallic polycondensation between cyclodiborazane-containing dibromide and 2,5-didodecyloxy-1,4-diethynylbenzene utilizing Sonogashira coupling. The polymerization was carried out under a nitrogen atmosphere, in THF/NEt3 solution in the presence of a catalytic amount of copper acetate, palladium chloride, and triphenylphosphine at 80 °C for 12 h. After reprecipitation into MeOH, the resulting polymer was isolated as a brown powder in moderate yield. The polymer obtained was soluble in common organic solvents such as THF, chloroform, and benzene, and its structure was confirmed by 1H NMR, 11B NMR, and IR spectra. The number-average molecular weight of the polymer was 8500 from the gel permeation chromatographic analysis (GPC, THF, PSt standards). In the UV−vis absorption spectrum recorded in chloroform, the absorption maximum was observed at 414 nm, owing to extension of π-conjugation via the vacant p-orbital of the boron atom and intramolecular charge transferred structure. This polymer exhibited an intense blue-green light emission upon irradiation at 414 nm.

CW blue-green light emission from GaN and SiC by sum-frequency generation and second harmonic generation

Continuous wave (CW) back-scattered sum-frequency generation (SFG) and second harmonic generation (SHG) have been obtained from GaN and SiC. GaN samples were obtained from GaN films grown by molecular-beam epitaxy (MBE), metalorganic chemical-vapor deposition and hydride vapor-phase epitaxy. The SiC samples were obtained from 3C SiC/Si grown by chemical vapor deposition (CVD), 4H and 6H single crystal SiC substrates. The samples were optically excited with two CW lasers at the red (840 nm) and the infrared (1.0 µm). SHG at 420 nm and 500 nm and SFG at 455 nm were observed. SFG and SHG were verified by measuring their relative intensities against the pumping laser power. The SHG signals from GaN and SiC samples are compared with that from KH2PO4 (KDP).

Synthesis and Properties of Light-Emitting Polymers Containing High Electron Attracting Groups

Two light-emitting polymers containing high electron attracting groups have been synthesized and their luminescent properties have been investigated. The synthesized polymers showed their absorption maxima at about 310 nm and the photoluminescence emission maxima at about 470 nm and 488 nm depending on the substituents. Single layer electroluminescent (EL) devices using the polymers showed blue and blue-green light emission.

Blue-Green Light Emission from Self-Assembled Bipyridinium Thin Films

Abstract The photoluminescence (PL) properties of a short ribbon-like conjugated bipyridinium and its application in the design and fabrication of organic LED devices were discussed.

The electroluminescence from porous β-SiC formed on C + implanted silicon

We report the preparation of silicon-based porous β-SiC visible light-emitting diodes. Carbon ions were implanted into crystal silicon wafers at an energy 50 keV and with a dose of 2 × 10 17 cm −2 followed by thermal annealing. A layer of polycrystalline β-SiC was formed beneath the sample surface. Porous structures including porous β-SiC and underlying porous Si were prepared by conventional anodization. Experimental cells composed of semitransparent Au/porous SiC/porous Si/p-Si/Al contact were prepared. A stable visible (blue-green) light emission was observed at a forward bias. The emission mechanism is also discussed.