Photoluminance Research Articles

Surface plasmon-enhanced quantum dot light-emitting diodes by incorporating gold nanoparticles.

Surface plasmon-enhanced electroluminescence (EL) has been demonstrated by incorporating gold (Au) nanoparticles (NPs) in quantum dot light-emitting diode (QLED). Time-resolved photoluminescence (TRPL) spectroscopy reveals that the EL enhancement is ascribed to the near-field enhancement through an effective coupling between excitons of the quantum dot emitters and localized surface plasmons around Au NPs. It is found that the size of Au NPs and the distance between the Au NPs and the emissive layer have significant effects on the performance of QLED. The enhancement can be maximized as the SP resonance wavelength of Au NPs matches well with the PL emission wavelength of the QD film and the distance between Au NPs and the emissive layer maintains 15 nm. The photoluminance (PL) and EL intensity can be enhanced by 4.4 and 1.7 folds with the incorporation of Au NPs. The maximum current efficiency of 4.56 cd/A can be achieved for the resulting QLEDs by incorprating Au NPs with an enhancement factor of 2.0. In addition, the enhancement ratio of 2.2 can be achieved for the lifetime of resulting QLED.

Fascinating functional properties of Mn:Gd2O3 nanocrystalline phosphor

In the present work we through the light on some of the fascinating structural, magnetic and optical properties of Mn:Gd2O3 nanophosphor. Manganese substituted nanocrystalline Mn:Gd2O3 was prepared via a sol gel procedure. The prepared samples were characterized applying X-ray diffraction (XRD), infrared spectroscopy (IR), squid magnometer and photoluminance (PL). XRD and IR analysis revealed a single phase solid solution up to x=0.2. The cation distribution of Mn and Gd between the crystallographically non-equivalent sites 8b and 24d of the space group Ia3¯ is found to be preferentially for all samples. The lattice parameter decreases with composition x, accompanied with systematic variation in the r.m.s. microstrain 〈εL2〉1/2.The magnetic measurement showed negative values for curie paramagnetic temperatures, θ, which indicates an antiferromagnetic interaction between the magnetic ions in Mn:Gd2O3. PL spectra showed a series of emission lines in the room temperature fluorescence measurements under UV excitation (220nm). The observed emission lines are stokes-shifted and the non-linearity optical phenomenon is confirmed. Further, the emission lines are slightly shifted with Mn concentration (x). The blue emission around (390–402) nm was appeared due to Mn doping. Because of its fascinating properties, Mn:Gd2O3 is recommended for fuel cells, photocatalytic, and biomedical applications.

Size induced ferromagnetism in pristine indium oxide nanoparticles

Indium oxide (In2O3) nanoparticles exhibit finite-size driven ferromagnetic behavior. Samples having sufficiently small particle size are ferromagnetic whereas samples with larger size show nonmagnetic behavior. X-ray diffraction confirms polycrystalline cubic bixbyite structure of In2O3. X-ray photoemission spectroscopy (XPS) and Photoluminance (PL) spectroscopy identify significant number of oxygen vacancies with effective concentration increasing with decreasing particle size. Magnetic characterizations reveal that the observed ferromagnetism is induces and stabilizes in small particles with significant number of oxygen vacancies. The observed intrinsic ferromagnetic interactions are attributed to the defect density and corresponding finite size effect.

Synthesis of g-C3N4/BiOClxBr1−x hybrid photocatalysts and the photoactivity enhancement driven by visible light

In the current investigation, we report a facile preparation of a series of novel g-C3N4/BiOClxBr1−x hybrid photocatalysts and their enhanced photoactivity under visible light irradiation. The physicochemical and optical absorption of as-prepared g-C3N4/BiOClxBr1−x were characterized by means of X-ray diffraction (XRD), filed-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR) and UV–vis diffuse reflection spectroscopy (DRS). A substantial decrease in photoluminance (PL) intensity of as-prepared hybrid photocatalyst compared to g-C3N4 is because of carries transfer between g-C3N4 and BiOClxBr1−x solid solution. The florescence lifetimes of g-C3N4 and the corresponding hybrid photocatalyst were measured using time correlated single photon counting (TCSPC) as well. Both DFT calculations and Mulliken electronegativity method were employed to calculate band edges in BiOClxBr1−x solid solutions. The high carries separation efficiency at the interface, between g-C3N4 and BiOClxBr1−x, of the hybrid photocatalyst renders g-C3N4/BiOClxBr1−x highly photocatalytically active. The hybrid catalyst showed excellent stability and efficiency even after many runs of photodegradation experiments.

Effect of Pressure and Temperature on Nucleation and Growth Kinetics of Titanium Oxide Nanoparticles

With the development of advanced processing and characterization tools, nanotechnology is emerging as a potential area which can deal with energy and environmental challenges. Titanium oxide nanoparticles are redox active nanoparticles and used in various applications as catalyst. The catalytic property of these nanoparticles varies with the phase, size, shape and environment. Phase and size of TiO2 nanoparticles varies significantly with the processing temperature and pressure. In this present work, TiO2 nanoparticles are synthesized at different temperature from sub-zero to 200°C with varying pressure (1atm-500psi) and time (1-144hrs). TiO2 nanoparticles are obtained by the hydrolysis of titanium isopropoxide precursor. The objective of this study is to understand the effect of pressure and temperature on nucleation and growth kinetics of synthesized TiO2 nanoparticles. These nanoparticles are characterized using x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), fourier transform infrared (FR-IR) spectroscopy, visible and ultra violet (UV-Vis) spectroscopy, and photo luminance (PL).

Effect of different concentration Li-doping on the morphology, defect and photovoltaic performance of Li–ZnO nanofibers in the dye-sensitized solar cells

Low concentrations of Li in Li-doped ZnO nanofibers prepared using hydrothermal method at low temperature can introduce oxygen vacancies and intrinsic Zn ions into the structure. Photo-luminance (PL) was used to investigate oxygen vacancies in the structure of ZnO nanofibers prepared by lower annealing temperature, and the XPS technique was also employed to satisfy the PL analysis results. PL analysis showed that oxygen vacancies increase in conjunction with Li concentrations. A shift in the lower angle of XRD patterns also demonstrates the defect in ZnO structure related to Li doping. Higher-efficiency DSSCs were obtained from the lower Li concentration of 0.01 M in ZnO nanofibers. Higher concentrations of Li tended to produce large amounts of cross-like nanofibers, which increase the open circuit voltage of the DSSCs. The highest open circuit voltage (Voc) obtained was 750 mV, which was higher than the best reported ZnO nanofibers-based DSSCs. Intensity modulation photocurrent spectroscopy (IMPS) and intensity modulation photo-voltage spectroscopy (IMVS) analysis showed that low amounts of Li-doping improved the electron injection efficiency of ZnO nanofibers in DSSCs. Lower recombination rates with higher electron transfer efficiency for 0.01 M Li-doped DSSCs exhibited higher efficiency of 0.59% than non-doped ZnO nanofibers DSSCs.

Sol–gel synthesis of ZnS (O,OH) thin films: Influence of precursor and process temperature on its optoelectronic properties

This study investigates the effect of sintering temperature and precursor composition on sol–gel deposition of ZnS (O,OH) on its structural and optoelectronic properties. ZnS (O,OH) thin films were prepared from stoichiometric, excess Zn and excess S precursor solutions. It was found that sintering temperature and precursor composition have strong effect on subsequent optoelectronic properties. From the combined photoluminance (PL) and EDS analysis it was revealed that beyond critical sintering temperature, oxygen incorporation occurs and results in PL emission at around 423nm.

Optical properties of SiOC film by PL spectrometer and reflectance

SiOC films made by the inductive coupled plasma chemical vapor deposition were analyzed by the photo luminance spectra and reflectance. Chemical shift obtained by PL spectra was observed and the reflectance was decreased at sample with low refractive index. The refractive index was in inverse proportion to the thickness of SiOC film. Lowering the reflectance caused to decrease the energy band gap and polarization, so increased an absorbance of the light. Low polarization of SiOC film was induced from the recombination and dissociation of alkyl sites by neighboring high electro negative oxygen. The electron affinity related to the energy band gap at surfaces increased at sample with low polarization, and finally, the reflectance decreased according to the reduction of polarity.

Synthesis of fluorene‐based hyperbranched polymers for solution‐processable blue, green, red, and white light‐emitting devices

AbstractFor the purpose of making hyperbranched polymer (Hb‐Ps)‐based red, green, blue, and white polymer light‐emitting diodes (PLEDs), three Hb‐Ps Hb‐terfluorene (Hb‐TF), Hb‐4,7‐bis(9,9′‐dioctylfluoren‐2‐yl)‐2,1,3‐benzothiodiazole (Hb‐BFBT), and Hb‐4,7‐bis[(9,9′‐dioctylfluoren‐2‐yl)‐thien‐2‐yl]‐2,1,3‐benzothiodiazole (Hb‐BFTBT) were synthesized via [2+2+2] polycyclotrimerization of the corresponding diacetylene‐functionalized monomers. All the synthesized polymers showed excellent thermal stability with degradation temperature higher than 355 °C and glass transition temperatures higher than 50 °C. Photoluminance (PL) and electroluminance (EL) spectra of the polymers indicate that Hb‐TF, Hb‐BFBT, and Hb‐BFTBT are blue‐green, green, and red emitting materials. Maximum brightness of the double‐layer devices of Hb‐TF, Hb‐BFBT, and Hb‐BFTBT with the device configuration of indium tin oxide/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate)/light‐emitting polymer/CsF/Al are 48, 42, and 29 cd/m2; the maximum luminance efficiency of the devices are 0.01, 0.02, and 0.01 cd/A. By using host–guest doped system, saturated red electrophosphorescent devices with a maximum luminance efficiency of 1.61 cd/A were obtained when Hb‐TF was used as a host material doped with Os(fptz)2(PPh2Me2)2 as a guest material. A maximum luminance efficiency of 3.39 cd/A of a red polymer light‐emitting device was also reached when Hb‐BFTBT was used as the guest in the PFO (Poly(9,9‐dioctylfluorene)) host layer. In addition, a series of efficient white devices were, which show low turn‐on voltage (3.5 V) with highest luminance efficiency of 4.98 cd/A, maximum brightness of 1185 cd/m2, and the Commission Internationale de l'Eclairage (CIE) coordinates close to ideal white emission (0.33, 0.33), were prepared by using BFBT as auxiliary dopant. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Microwave-Assisted Synthesis of Shuttle-shaped Single-Crystalline Te Nanotubes Decorated with Spherical Particles

Shuttle-shaped single-crystalline Te nanotubes decorated with spherical particles on outer surface have been successfully synthesized in reaction media of polyol solvent through a simple and rapid microwave-assisted approach. The length, outer diameter and wall thickness of as-synthesized Te nanotubes were roughly measured at 5-15 μm, 300-500 nm and 100-150 nm, respectively. The crystal growth process of Te nanotubes was investigated and discussed as the key issue of this present study, and it was found that the scrollinggrowth- based mechanism would best account for the formation process of the shuttle-shaped Te nanotubes. Photoluminance (PL) measurements displayed that the as-synthesized Te nanotubes can not only give strong violet blue emission but also strong red emission, and such unique optical property could be beneficial for nano-optical applications. Keywords: Te nanotubes, microwave-assisted, polyol, photoluminance, Shuttle-shaped, Spherical Particles, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM)

Effects of bifunctional linker on the optical properties of ZnO nanocolumn-linker-CdSe quantum dots heterostructure

We study the effects of bifunctional linker on the optical properties of ZnO nanocolumn-linker-CdSe quantum dots heterostructure. The CdSe quantum dots are anchored on the surface of ZnO nanocolumns through either aliphatic linker of 3-aminopropyl trimethoxysilane (APS) or aromatic linker of p-aminophenyl trimethoxysilane (APhS). X-ray photoelectron spectroscopy is used to confirm the bifunctional linker bound onto CdSe quantum dots and onto the ZnO nanocolumns. The TEM study reveals a CdSe quantum dot shell of about 15 nm coated on the ZnO nanocolumns. The photoluminance (PL) spectroscopy and time-resolved PL spectroscopy of ZnO nanocolumn-linker-CdSe quantum dots reflects that the photo-induced electron transfer across the interface of ZnO and CdSe through the aromatic APhS is more efficient than the aliphatic APS. This study demonstrates that through the usage of appropriate surface linker, the charge transfer rate across the interfaces of donor/acceptor (D/A) heterostructure can be improved for potential photovoltaic cell applications.

White organic light-emitting diodes showing nearly 100% internal quantum efficiency

The authors have demonstrated white organic light-emitting diodes (WOLED) using all phosphorescent emitters for blue, green, and red, such as FCNIrpic, Ir(ppy) 3 and Ir(pq) 2(acac). Various electron-transporting materials such as Bebq 2, BPhen, TAZ, BAlq, and TPBI were also investigated for improving quantum efficiency of phosphorescence of WOLED by fabricating and characterizing white devices using these materials as an electron-transporting layer (ETL). It was found that WOLED with an ETL of TPBI exhibits a peak external quantum efficiency (EQE) of 19.5% and a peak power efficiency of 39.2 lm/W at very low light intensity. The optimized device also shows an EQE of 16.4% at 1000 cd/m 2. It was also found that the optimized white device with TPBI shows minimal change with Δ Commission Internationale de I’Eclairage coordinates of ±(0.02, 0.00) from 100 to 10,000 cd/m 2. In order to understand the mechanism for achieving nearly 100% IQE with this device structure, various analyses were also executed, such as UV/visible absorbance measurements of FCNIrpic and photoluminance (PL) measurements of mCP, fabrications of hole- and electron-only devices, UV/visible absorbance measurements of Ir(ppy) 3 and Ir(pq) 2(acac) and PL of FCNIrpic, and surface roughness measurements of various ETL films.

White-light Emitting ZnO-SiO2 Nanocomposite Thin Films Prepared by Sputtering Method

ABSTRACTZnO-SiO2 nanocomposite thin films were prepared using RF sputtering method without substrate heating. The photoluminance (PL) measurements showed that the ZnO-SiO2 nanocomposite thin films are able to emit white light consisting of violet, blue, and green-yellow band emissions. The blue emission was attributed to the large amount of ZnO/SiO2 interfaces, which enlarges the depletion layer width and then enhances the related transition. Further analyses indicated that the defect structure of samples could be manipulated by the amount and distribution of ZnO nanoparticles in SiO2 matrix to yield distinct luminescence property.