Near-infrared Electroluminescence Research Articles

Features of the electroluminescence spectra of quantum-confined silicon p +-n heterojunctions in the infrared spectral region

The results of studying the characteristics of optical emission in various regions of quantum-confined silicon p+-n heterojunctions heavily doped with boron are analyzed. The results obtained allow one to conclude that near-infrared electroluminescence arises near the heterointerface between the nanostructured wide-gap silicon p+-barrier heavily doped with boron and n-type silicon (100), the formation of which included the active involvement of boron dipole centers.

Near-Infrared and White Organic Light Emitting Diodes Based on a Samarium Complex

Photoluminescence (PL) and electroluminescence (EL) properties of a samarium complex Sm(DBM)(3)phen (DBM = dibenzoylmethane, phen = 1,10-phenanthroline) were investigated in both visible and near-infrared (NIR) regions. A series of organic light emitting devices based on Sm(DBM)3phen were fabricated. The device performances were strongly dependent on the hole transportation layer/emitting layer (HTL/EML) interface properties. When using N,N'-diphenyl-N,N-di(m-tolyl)-benzidine (TPD) as HTL, intense NIR EL irradiance could be achieved, accompanied with orange EL emission. When N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-[1,1-biphenyl]-4,4'-diamine (NPB) was used as HTL, exciplex formed at the HTL/EML interface, and white light emission could be achieved under high operating voltage, due to the integrating of the blue emission from the exciplex and orange emission from Sm3+ ion. Better white organic light emitting diodes (WOLEDs) could be achieved when a ladder HTL 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) was introduced into the device, that the device showed bright stable white emission properties under all operating voltages. This work provided a feasible way for the design and fabrication of NIR and WOLEDs with simple device structures.

Photo- and electroluminescence from deep-red- and near-infrared-phosphorescent tris-cyclometalated iridium(III) complexes bearing largely π-extended ligands

Deep-red- and near-infrared-phosphorescent tris-cyclometalated iridium(III) complexes bearing largely π-extended cyclometalated (C^N) ligands were newly synthesized, and their photo- and electroluminescence properties were investigated. When 2-(benzo[b]furan-2-yl)quinoline and 2-(benzo[b]thiophen-2-yl)quinoline were employed as C^N ligands, deep-red photoluminescence was obtained (Ir-1a and Ir-1b; λPL in CH2Cl2, 647 and 652nm, respectively). In the case of the isoquinoline analogues of Ir-1a and Ir-1b, emission maxima were further red-shifted, ranging from deep-red to near-infrared regions (Ir-2a and Ir-2b; λPL in CH2Cl2, 696 and 690nm, respectively). Especially, Ir-2b showed an excellent photoluminescence quantum yield (ΦPL=0.15), and a polymer light-emitting diode doped with Ir-2b exhibited deep-red–near-infrared electroluminescence with a high external quantum efficiency (λEL=694nm, ηext max=1.41%).

Electroluminescence from Cr3+ in Perovskite Thin-Film Phosphors Using LaAlO3 and LaGaO3 as Hosts

We observed multicolor and near-infrared electroluminescence (EL) from perovskite oxide thin-film phosphors using Cr- and Ce-co-doped LaGaO3 and LaAlO3. These phosphor thin films were prepared by varying either Cr or Ce content using a combinatorial r.f. magnetron sputtering deposition method. Intense deep-red and weak yellow-green EL emissions were observed from thin-film electroluminescent (TFEL) devices fabricated using posannealed LaGaO3:Ce,Cr thin films. Intense near-infrared emission and yellow-green EL emissions were observed from TFEL devices fabricated using posannealed LaAlO3:Ce,Cr thin films. The highest EL intensity was obtained in TFEL devices using postannealed LaGaO3:Ce,Cr and LaAlO3:Ce,Cr phosphor thin films with Cr content approximetly 3 and 1at.%, respectively. All the observed emission peaks in EL from the LaGaO3:Ce,Cr and/or the LaAlO3:Ce,Cr phosphor thin films were assigned to either the emission originating from the transition in the Ce3+ and Cr3+ ions.

Green, near-infrared electroluminescence of novel yttrium tetrazole complexes

Four novel yttrium complexes with the molecular formula Y(Tz)n(x)2(SCN)3−n(H2O), n = 2, 3 and x = phen, bpy, were synthesized by the reactions of yttrium salt with 5-phenyl tetrazole (Tz), 1,10-phenanthroline (phen), 2,2-bipyridine (bpy) and thiocyanate ions, and were used as the emitting material in electroluminescent devices. The structures of these complexes were determined by UV-visible and FT-IR spectroscopy, 1H NMR, CHN analysis and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The monodentate mode of the Tz complexes was investigated by FT-IR spectroscopy. The different structures of the compounds suggest the importance of the tetrazole and auxiliary ligands in the emission properties of the yttrium complexes. It was found that the Y–polypyridine complexes dressed by tetrazole antennas have highly efficient intra-energy transfer. The Y complexes exhibited broad ligand-centered electroluminescence with maximum near 550 nm, and near-IR electroluminescence at 800, 900 and 950 nm. The electroluminescence spectra of the yttrium complexes indicated a long red shift in the visible region compared to the PVK:PBD blend. The reaction details and features were described and discussed.

Near-infrared electroluminescence emission from an n-InN nanodots/p-Si heterojunction structure

An n-InN nanodots/p-Si(1 1 1) heterojunction diode was fabricated by plasma-assisted molecular beam epitaxy. The device shows clear rectifying behaviour with a turn-on voltage of approximately 1.2 V at room temperature. The near-infrared electroluminescence (EL) can be observed under forward bias, which covers a wide wavelength range. In comparison with the photoluminescence spectra, the maximum of the EL spectra has a blueshift which is probably due to the size quantization effect of small-sized InN nanodots and their stronger contribution to the EL intensity. On the other hand, there is an obvious enhancement of the less dominant transitions on the short wavelength side of the EL spectra, which may arise from the recombination of the injected holes with the extremely high-density surface electrons of InN nanodots.

Near-infrared electroluminescence from organic light emitting diode based on Imine oligomer with low turn on voltage

We demonstrated an efficient near infrared (NIR) electroluminescence from organic light emitting diode based on Imine oligomer. Electroluminescence with peak emission wavelengths of 800nm were observed from the oligomer studied here. High performance organic light-emitting device is obtained using this materials as a near-infrared emitter with maximum external quantum efficiency, electrical-to-optical power efficiency and low turn on voltage of 1.9%, 8.55mW/W and 2.3V, respectively. The emitter energy levels are calculated using Gaussian 03 program.

Near-infrared electroluminescence in ErYb silicate based light-emitting device

We report the first observation of near-infrared electroluminescence (EL) in ErYb silicate based metal–insulator–semiconductor (MIS) light-emitting device. The ErYb silicate thin film and the device were fabricated on silicon substrate using the standard silicon technology. The EL spectrum at 1.53μm was observed under a current density of 1.2mA/cm2. The conduction mechanism of the device was Fowler–Nordheim tunneling and the EL mechanism was attributed to the direct impact excitation of Er ions by the hot electrons produced by the high electric field in the silicate layer.

Near infrared electroluminescence from n-InN/p-GaN light-emitting diodes

Undoped InN thin film was grown on p-GaN/Al2O3 (0001) template by molecular beam epitaxy. Near-infrared (NIR) electroluminescence (EL) that overlapped the optical communication wavelength range was realized using the n-InN/p-GaN heterojunction structure. The light emitting diode showed typical rectification characteristics with a turn-on voltage of around 0.8 V. A dominant narrow NIR emission peak was achieved from the InN side under applied forward bias. By comparing with the photoluminescence spectrum, the EL emission peak at 1573 nm was attributed to the band-edge emission of the InN film.

Strong visible and near-infrared electroluminescence and formation process in Si-rich polymorphous silicon carbon

We report here a strong and stable electroluminescence (EL) from Si-rich hydrogenated polymorphous silicon carbon thin films (pm-Si1-xCx : H) fabricated in a plasma-enhanced chemical vapor deposition system. We investigate an unusual forming process in the pm-Si1-xCx : H thin films, during initial EL stressing, and propose a current-stress-induced phase separation process for the formation of new Si nanoclusters, which give rise to strongly enhanced emissions in both visible and near infrared ranges at 1.8–2.1 eV and 0.8–1.2 eV, respectively. The sub-crystalline-Si-bandgap emission is particularly attractive to realize a Si-based multi-band light source for optical interconnection and telecommunication.

Near-infrared electroluminescence from double-emission-layers devices based on Ytterbium (III) complexes

We investigated near-infrared electroluminescence properties of two lanthanide complexes Yb(PMBP)3Bath [PMBP = tris(1-phenyl-3-methyl-4-(4-tert-butylbenzacyl)-5-pyrazolone); Bath = bathophenanthroline] and Yb(PMIP)3TP2 [PMIP = tris(1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone); TP = triphenyl phosphine oxide] by fabricated the double-emission-layers devices. From the device characteristics, it is known that holes are easier to transport in Yb(PMIP)3TP2 layer and electrons are easier to transport in Yb(PMBP)3Bath layer, at the same time, both of the two complexes can be acted as emission layers in the device. The recombination region of carriers has been confined in the interface of Yb(PMIP)3TP2/Yb(PMBP)3Bath, and pure Yb3+ ion characteristic emission centered at 980nm has been obtained. The device shows the maximum near-infrared irradiance as 14.7mW/m2 at the applied voltage of 17.8V.

Linear and Cyclic Porphyrin Hexamers as Near-Infrared Emitters in Organic Light-Emitting Diodes

Here we report organic light-emitting diodes incorporating linear and cyclic porphyrin hexamers which have red-shifted emission (λ(PL) = 873 and 920 nm, respectively) compared to single porphyrin rings as a consequence of their extended π-conjugation. We studied the photoluminescence and electroluminescence of blends with poly(9,9'-dioctylfluorene-alt-benzothiadiazole), demonstrating a high photoluminescence quantum efficiency of 7.7% for the linear hexamer when using additives to prevent aggregation and achieving high color purity near-infrared electroluminescence.

Near-Infrared Organic Light-Emitting Diodes Based on Donor-pi-Acceptor Oligomers

This letter reports efficient near-infrared (NIR) electroluminescence (EL) of organic light-emitting diodes (OLEDs) based on two donor-pi-acceptor oligomers. The energy gap can be tuned by changing the conjugated length, strengths of the acceptor component, and nonplanarity. EL with peak emission wavelengths of 775 and 905 nm were observed from the two NIR oligomers. External quantum efficiencies up to 3.54%, electrical-to-optical power efficiencies up to 15.8 mW/W, and turn-on voltage of 4.5 V were achieved in OLEDs based on these NIR emitters.

Red electrophosphorescent platinum(II) quinolinolate complexes

Luminescent organoplatinum complexes featuring 8-quinolinolates as chelating ligands have been synthesized and characterized. Substitution of the quinolinolate ligand has been achieved in the 5 position, where benzoyl substituents were introduced by reacting 8-hydroxyquinoline and the corresponding benzoyl chloride in a Friedel–Crafts acylation. The resulting complexes, κ2(N,C2)-(2-(4-tert-butylphenyl)pyridine)-κ2(N,O)-(5-(4-tert-butylphenyl)(8-quinolinolato-5-yl)methanone)platinum(II) and κ2(N,C2)-(3-hexyloxy-2-phenylpyridine)-κ2(N,O)-((8-quinolinolato-5-yl)phenylmethanone)platinum(II), have been investigated by nuclear magnetic resonance and infrared spectroscopy, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, X-ray analysis, thermal analysis, cyclic voltammetry, UV–vis absorption spectroscopy, and luminescence measurements in solution and in the solid state. The solid-state structures of the complexes were found to be dominated by π–π intermolecular interactions. Organic light-emitting devices based on the complexes and a matching host material gave red to near-infrared electroluminescence with low-onset voltages (4–5 V) and continuous wave luminance intensities exceeding 500 cd/m2.

Near-infrared electroluminescence and stimulated emission from semiconducting nonconjugated polymer thin films

We present the results of a study on near-infrared electroluminescence and optical amplification in semiconductor thin films based on a nonconjugated polymer doped with luminescent and electron-transport molecules. A single-layer light-emitting diode is fabricated on an indium tin oxide-coated glass substrate with poly(9-vinylcarbazole) containing an electron-transport material, 2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole and a near-infrared-emitting compound, 2-(6-(p-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl)-3-ethylbenzothiazolium perchlorate. The single-layer structure shows near-infrared electroluminescence with a turn-on voltage of 13 V. The same structure is characterized under transversal pulsed photopumping with a frequency-doubled Nd: yttrium aluminum garnet laser. With increasing pump fluence, the edge emission at 0.82 μm shows both significant gain narrowing and superlinear intensity increase, which indicate the existence of optical gain by stimulated emission. Our results provide impetus for the development of near-infrared polymer lasers and optical amplifiers.

Electroluminescence from Electrolyte-Gated Carbon Nanotube Field-Effect Transistors

We demonstrate near-infrared electroluminescence from ambipolar, electrolyte-gated arrays of highly aligned single-walled carbon nanotubes (SWNT). Using electrolytes instead of traditional oxide dielectrics in carbon nanotube field-effect transistors (FET) facilitates injection and accumulation of high densities of holes and electrons at very low gate voltages with minimal current hysteresis. We observe numerous emission spots, each corresponding to individual nanotubes in the array. The positions of these spots indicate the meeting point of the electron and hole accumulation zones determined by the applied gate and source-drain voltages. The movement of emission spots with gate voltage yields information about relative band gaps, contact resistance, defects, and interaction between carbon nanotubes within the array. Introducing thin layers of HfO(2) and TiO(2) provides a means to modify exciton screening without fundamentally changing the current-voltage characteristics or electroluminescence yield of these devices.

Sensitized infrared electrophosphorescence based on divalent copper complex by an iridium(III) complex

We demonstrate enhanced near-infrared (NIR) electroluminescence (EL) of copper phthalocyanine (CuPc) phosphor doped organic light emitting diodes (OLED) by introducing a red phosphor, bis(1-phenylisoquinolinato) iridium(III) acetylacetonate (Ir(piq) 2acac). For the codoped device, due to presence of Ir(piq) 2acac, the NIR emission peaked at 1120 nm of CuPc was increased by 15 times comparing with the CuPc monodoped device. The enhancement of NIR emission of CuPc emitter was principally attributed to an energy transfer from Ir(piq) 2acac to CuPc, and the sensitized mechanism was also discussed in detail.

Red and near-infrared electroluminescence from organic light-emitting devices based on a soluble substituted metal-free phthalocyanine

Red and near-infrared (NIR) organic light-emitting devices (OLEDs) were fabricated based on Tetra (2-Isopropyl-5-methylphenoxyl) substituted metal-free phthalocyanine (Tetra-H 2Pc). The devices were fabricated by vacuum deposition and spin coating methods. The electroluminescence (EL) intensity at about 910 nm in the devices based on Tetra-H 2Pc was increased by about 14 times compared with the intensity at about 930 nm in the devices based on unsubstituted metal-free phthalocyanine (H 2Pc) in the same device structures. The improvement in the EL intensity was attributed to the large steric hindrance of non-peripheral phenoxyl substituent of Tetra-H 2Pc. It was found that the NIR EL spectra of the doped devices exhibited a strong dependence on the concentration of Tetra-H 2Pc. The emission at 740 nm was from Tetra-H 2Pc monomer, while the emissions around 910 nm and 870 nm were from excimer or higher aggregated species.

Highly efficient near-infrared hybrid organic-inorganic nanocrystal electroluminescence device

We report the use of PbS nanocrystals within a hybrid device that emits 1.2μm electroluminescence with an external quantum efficiency of 1.15% corresponding to an internal quantum efficiency of ∼5%–12% thus demonstrating a viable, low-cost, highly efficient near infrared organic electroluminescent device. Direct generation of the excited state on the nanocrystal result in eliminating competing processes that have previously led to the low reported efficiencies in near-infrared light emitting devices. Furthermore, the emission wavelength can be tuned to cover a wide range of wavelengths including the 1.3–1.5μm region without significant change of the efficiency.

Spectroscopic Analysis on Metal-Oxide-Semiconductor Light-Emitting Diodes with Buried Si Nanocrystals and Nano-Pyramids in SiOx Film

The ordered arrays of magnetic metal (including Fe, Co and Ni) nanotubes and nanowires encapsulated with carbon tubes are controllably synthesized by employing the array of C tubes as second-order template and combining with electrodeposition technique. The wall thickness and diameter of carbon nanotubes are uniform along the whole tubes; also the wall thickness of inner metal nanotubes is adjustable from 25 nm to solid nanowires. These composite structures are characterized by X-ray diffractometer (XRD), energy-dispersive spectrometry (EDS), Raman scattering spectrum, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The magnetic properties show that coaxial nanotubes and nanocables composite arrays all exhibit magnetic anisotropy with the easy direction perpendicular to axis of the metal nanotubes or nanowires except the Ni at C coaxial nanotubes array that has no preferable magnetization axis.