Double-peak Emission Research Articles

Random laser action with nanostructures in a dye solution

Photoluminescence of Rhodamine B dye solution containing nanostructures of titanium dioxide (nanoparticles, nanorods, and nanotubes) was investigated at various optical excitation intensities. The stimulated emission was observed owing to multiple scattering of photons in the dye solution. The threshold intensity, emission wavelength, and profile of stimulated emission are different for different nanostructures. Single and double emission peaks were observed, respectively, at low (10−3 M) and high (10−2 M) dye concentrations. The stimulated emission characteristics with nanostructures dispersed in dye solution are attributed to the nonresonant scattering.

Emissions of CH4 and N2O under Different Tillage Systems from Double-Cropped Paddy Fields in Southern China

Understanding greenhouse gases (GHG) emissions is becoming increasingly important with the climate change. Most previous studies have focused on the assessment of soil organic carbon (SOC) sequestration potential and GHG emissions from agriculture. However, specific experiments assessing tillage impacts on GHG emission from double-cropped paddy fields in Southern China are relatively scarce. Therefore, the objective of this study was to assess the effects of tillage systems on methane (CH4) and nitrous oxide (N2O) emission in a double rice (Oryza sativa L.) cropping system. The experiment was established in 2005 in Hunan Province, China. Three tillage treatments were laid out in a randomized complete block design: conventional tillage (CT), rotary tillage (RT) and no-till (NT). Fluxes of CH4 from different tillage treatments followed a similar trend during the two years, with a single peak emission for the early rice season and a double peak emission for the late rice season. Compared with other treatments, NT significantly reduced CH4 emission among the rice growing seasons (P<0.05). However, much higher variations in N2O emission were observed across the rice growing seasons due to the vulnerability of N2O to external influences. The amount of CH4 emission in paddy fields was much higher relative to N2O emission. Conversion of CT to NT significantly reduced the cumulative CH4 emission for both rice seasons compared with other treatments (P<0.05). The mean value of global warming potentials (GWPs) of CH4 and N2O emissions over 100 years was in the order of NT<RT<CT, which indicated NT was significantly lower than both CT and RT (P<0.05). This suggests that adoption of NT would be beneficial for GHG mitigation and could be a good option for carbon-smart agriculture in double rice cropped regions.

Sr5-x(PO4)2SiO4∶xEu2+磷灰石荧光粉的发光性能及LED应用研究

采用高温固相法在还原气氛下合成了Sr5-x(PO4)2SiO4∶xEu2+磷灰石型荧光粉。通过XRD、PL、SEM对样品的晶体结构、激发和发射光谱以及形貌进行了表征。在Eu2+浓度较低时,Eu2+占据不同的晶体格位而形成两个发光中心,发射光谱具有双发射峰;随着掺杂浓度的增加,Eu2+之间的能量传递使黄光区域的发射峰强度逐步增强,并在x=0.075时达到最大值。发射光谱红移可能是Eu2+受晶场强度和能量传递共同作用的结果。考察了该材料在白光LED中的封装应用性能,其双发射峰有助于提升白光LED光源的显色性。

White Organic Light-Emitting Diode Using the Exciplex Between DNTPD and ET-137

Two organic layers of the N,N′-diphenyl-N,N′-bis-[4-(phenyl-m-tolyl-amino)-phenyl]-biphenyl-4,4′-diamine [DNTPD] and the ET-137 which is a pyran derivative provided from SFC Co. were sequentially deposited between the ITO anode and the LiF/Al cathode for generating blue light-emitting excitons in the electron transport material and yellow light-emitting exciplexes at the interface of two organic layers. In this study, the DNTPD was used as a hole transport layer and the ET-137 as an electron transport and exciton formation layer. The structure of the fabricated devices is very simple compared with those of conventional white organic light-emitting devices (OLEDs) and the emission showed the nearly pure white on the Commission Internationale de I′ Eclarirage (CIE) chart. The device with two organic layers of 500Å-thick DNTPD and 500Å-thick ET-137 showed electroluminescent characteristics of the double peak emission with a peak wavelength of 455 nm from the excitons of ET-137 and a peak wavelength of 561 nm from the exciplexes at the interface of DNTPD and ET-137, the maximum current efficiency of 1.8 cd/A, and the color coordinates of (0.32, 0.37) on the CIE chart.

Mass Transfer in Two Post-AGB Binaries with Dusty Disks

Abstract We present a time series of high-resolution spectra for two poorly studied candidate post-AGB stars surrounded by dusty disks, BD+46 442 and IRAS 19135+3937. We find that both stars show radial velocity variations with periods of 130-140 days. IRAS 19135+3937 has been previously classified as a semi-regular variable based on the light variations with a similar period, but our spectra reveal an evolved star which is too warm to be on the AGB. the variability of BD+46 442 has not been studied till now. the stars reveal a number of spectroscopic peculiarities that resemble features in the interactive binaries including the S-type Symbiotics. Namely, H profile alternates between a double-peak emission and a P Cyg profile, which correlates with the radial velocity phase. A weak asymmetry is tentatively detected in the cross-correlation function that moves in anti-phase with the main component. In addition, strong photospheric lines reveal a narrow central absorption. We conclude that these peculiarities are consistent with a picture where the observed post-AGB stars orbit a much fainter companion at a sub-AU separation and transfer mass on it. the companion is surrounded by an accretion disk, possibly with some kind of an outflow. the SED shows that whole system is surrounded by stable dusty disk as well. It remains to be seen with more observations how much of the line asymmetry could be due to the contribution of low-amplitude pulsations.

Time-resolved spectroscopy of BD+46°442: Gas streams and jet creation in a newly discovered evolved binary with a disk

Previous studies have shown that many post-AGB stars with dusty disks are associated with single-lined binary stars. To verify the binarity hypothesis on a larger sample, we started a high-resolution spectral monitoring of about 40 field giants, whose binarity was suspected based on either a light curve, an infrared excess, or a peculiar chemical composition. Here we report on the discovery of the periodic RV variations in BD+46 442, a high-latitude F giant with a disk. We interpret the variations due to the motion around a faint companion, and deduce the following orbital parameters: Porb = 140.77 d, e = 0.083, asini=0.31 AU. We find it to be a moderately metal-poor star ([M/H]=-0.7) without a strong depletion pattern in the photospheric abundances. Interestingly, many lines show periodic changes with the orbital phase: Halpha switches between a double-peak emission and a PCyg-like profiles, while strong metal lines appear split during the maximum redshift. Similar effects are likely visible in the spectra of other post-AGB binaries, but their regularity is not always realized due to sporadic observations. We propose that these features result from an ongoing mass transfer from the evolved giant to the companion. In particular, the blue-shifted absorption in Halpha, which occurs only at superior conjunction, may result from a jet originating in the accretion disk around the companion and seen in absorption towards the luminous primary.

Characteristics of InAs/InGaAs/GaAs QDs on GeOI substrates with single-peak 1.3 µm room-temperature emission

GaAs-based quantum dot (QD) systems, especially InAs/InGaAs/GaAs QDs, have demonstrated superior device performances as compared with higher dimensional systems. However, to realize high-speed optical interconnects for Si-based electronics, one will need to grow the QDs on Si substrates. While it is promising to integrate the InAs/InGaAs/GaAs QDs on Si with the use of germanium-on-insulator-on-silicon (GeOI) substrates, reported results exhibit bimodal QD sizes and double emission peaks, i.e. unsatisfactory for realistic applications. In this paper, we showed that with an optimized GaAs buffer, single-peak 1.33 µm room-temperature emission can be obtained from InAs/InGaAs/GaAs QDs on GeOI substrates.

Effects of Fe doping on the crystal structures and photoluminescences of ZnO: Ni thin films prepared by sol-gel method

Zn0.95-xNi0.05FexO (x=0, 0.005, 0.01, 0.03, 0.05) thin films are fabricated on the glass substrates by the sol-gel method. The surface morphologies and crystal structures of the films are investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results reveal that preferential orientations are all along the (002) direction in all films. the qualities of ZnO: Ni films for low or high Fe concentration become worse, the crystal grain sizes of ZnO: Ni film are reduced, but moderate Fe doping seems to improve the film quality. XPS results reveal that Ni elements exist as Ni2+, and Fe elements exist as Fe2+ and Fe3+. Strong ultraviolet emission peaks, blue double emission peaks and green emission peaks are observed in the photoluminescence spectra of all samples at room temperature. It is found that the PL intensities of (Ni, Fe) co-doped ZnO films could be well modulated by Fe doping. In combination with other reports, we think that the ultraviolet emission peaks are due to exciton recombination; while the blue double peaks are caused by transition of electrons from the zinc interstitial to the top of the valence band or from the oxygen vacancy to the zinc vacancy. However, the green peak is highly dependent on oxygen vacancy and zinc vacancy formed by doping.

Synthesis and Optoelectronic Properties of Blue-Emitting Star-Burst Oligomers Based on Triphenylamine and Spiro(fluorene-9,9'-xanthene)

Three star-burst conjugated oligomers based on triphenylamine (TPA), fluorene and spiro (fluorene-9,9'-xanthene) (SEX) have been synthesized via the Sonogashira cross-coupling reaction. These well-defined oligomers possess high decomposition temperatures (T-d) at 417, 439, and 425 degrees C, respectively. Differential scanning calorimetry (DSC) demonstrates two oligomers which incorporate the SFX unit, TPA-SFX and TPA-SFXCz, possess higher glass transition temperatures (T-g) at 141 and 127 degrees C, respectively, compared with 101 degrees C for TPA-F. The investigation of their optical properties shows TPA-SFX and TPA-SFXCz exhibit a single blue emission in film with emission peaks at 434 and 442 nm, respectively, whereas TPA-F shows a broad double-peak emission located at 424 and 455 nm, which implies the nonplanar TPA and spiro SFX moieties can effectively restrict the formation of aggregates or excimers. Electrochemical investigations show that these oligomers have relatively high HOMO levels at around -5.4 eV due to incorporation of the electron-rich TPA core. Electroluminescence (EL) devices with a configuration of ITO (indium tin oxide)/PEDOT:PSS (poly(3,4-ethylenedioxythiophene): poly (styrenesulfonate))/oligomer/TPBI (1,3,5-tris(1-phenyl-1H -benzimidazol-2-yl)benzene)/LiF/Al were constructed using these oligomers as the emitter by spin-coating, with TPBI as the electron-transporting and hole-blocking layer. The device using TPA-SFX as the emitting layer exhibits bright blue emission with the maximum brightness and maximum current efficiency of 2680 cd . A(-2) and 0.35 cd . A(-1), and CIE. color coordination of (0.17, 0.13).

Spatial resolution of methods for measuring the light-emission profile in organic light-emitting diodes

An analysis is presented of the resolution limits of two alternative methods for deducing the light-emission profile in organic light-emitting diodes (OLEDs) from the angular and polarization dependent emission spectra. The comparison includes the “fit-profile” (FP) method, within which the known physics of the recombination process is employed to describe the shape of the profile using a strongly reduced number of degrees of freedom, and the Tikhonov method, which provides a more general solution. First, the cases of a delta-function shaped emission profile and a broad single-peak emission profile are investigated. It is demonstrated that for these cases a ∼1 nm resolution of the peak position may be obtained, provided that the peak is positioned optimally in the OLED microcavity. Subsequently, an analysis is given for a double-peak emission profile and for a rectangular profile, as may be obtained in multilayer OLEDs, revealing a resolution of ∼10 nm for the cases studied. It is suggested that, in general, an optimal analysis should be based on a combined Tikhonov-FP approach.

LINEAR POLARIZATION OF A DOUBLE PEAKED BROAD EMISSION LINE IN ACTIVE GALACTIC NUCLEI

A small number of active galactic nuclei are known to exhibit prominent double peak emission profiles that are well-fitted by a relativistic accretion disk model. We develop a Monte Carlo code to compute the linear polarization of a double peaked broad emission line arising from Thomson scattering. A Keplerian accretion disk is adopted for the double peak emission line region and the geometry is assumed to be Schwarzschild. Far from the accretion disk where flat Minkowski geometry is appropriate, we place an azimuthally symmetric scattering region in the shape of a spherical shell sliced with <TEX>${\Delta}{\mu}=0.1$</TEX>. Adopting a Monte Carlo method we generate line photons in the accretion disk in arbitrary directions in the local rest frame and follow the geodesic paths of the photons until they hit the scattering region. The profile of the polarized flux is mainly determined by the relative location of the scattering region with respect to the emission source. When the scattering region is in the polar direction, the degree of linear polarization also shows a double peak structure. Under favorable conditions we show that up to 0.6% linear polarization may be obtained. We conclude that spectropolarimetry can be a powerful probe to reveal much information regarding the accretion disk geometry of these active galactic nuclei.

A template-free sol–gel technique for controlled growth of ZnO nanorod arrays

The growth of ZnO nanorod arrays via a template-free sol–gel process was investigated. The nanorod is single-crystalline wurtzite structure with [0 0 0 1] growth direction determined by the transmission electron microscope. The aligned ZnO arrays were obtained directly on the glass substrates by adjusting the temperatures and the withdrawal speeds, without seed-layer or template assistant. A thicker oriented ZnO nanorod arrays was obtained at proper experimental conditions by adding dip-coating layers. Room temperature photoluminescence spectrum exhibits an intensive UV emission with a weak broad green emission as well as a blue double-peak emission located at 451 and 468 nm, respectively. Further investigation results show that the difference in the alignment of nanorods ascribes to the different orientations of the nanoparticles-packed film formed prior to nanorods on the substrate. Well ordered ZnO nanorods are formed from this film with good c-axis orientation. Our study is expected to pave a way for direct growth of oriented nanorods by low-cost solution approaches.

BaAl2O4:Eu2+, Dy3+ Nanotube Synthesis by Heating Conversion of Homogeneous Coprecipitates and Afterglow Characteristics

Hexagonal BaAl2O4:Eu2+, Dy3+ polynary complex nanotubes with long-lasting phosphorescence were obtained through a facile coprecipitation approach followed by a postcalcining reaction in a weak reducing atmosphere. In the case of low annealing temperature, anion vacancies and surface stress can induce lattice contraction due to poor crystallininty; moreover, Eu2+ ions can occupy two different crystallographic Ba2+ sites due to low symmetry, resulting in an appearance of double emission peaks. For the sample annealed at higher temperature, however, Eu2+ ions only occupy substitutedly the Ba2+ sites with lowest energy due to high crystallinity; moreover, as compared to the sample annealed at low temperature, its emission band redshifts as the results of both high crystal symmetry around Eu2+ ions and large average optical path. Additionally, Eu2+ and Dy3+ ions substitute incompletely for Ba2+ sites in nanostructures, leading to the decrease of effective electron trap densities and depths, and therefore tubular nanostructures show fast afterglow decay rate in comparison with the bulk counterpart.

TPBI:FIrpic organic light emitting devices with the electron transport layer of Bphen/Alq 3

Bluephosphorescent organic light emitting devices (PhOLEDs) using 1,3,5-tris(N-phenylbenzimiazole-2-yl)benzene[TPBI] as a host and bis((4,6-difluorophenyl)-pyridinate-N,C2′)picolinate [FIrpic] as a dopant in the emitter were fabricated with different treatments of electron transport layer(ETL). The device with an ETL of 4,7diphenyl-1,10-phenanthroline [Bphen] (device A) showed higher current density and luminance under the same applied voltages than the device with an ETL of aluminum-tris-8-hydroxyquinoline [Alq 3] (device B). On the other hand, the device with an ETL of Alq 3 showed better roll-off characteristics in the current efficiency degradation according to the voltage increase than the device with an ETL of Bphen. The device with an ETL of Bphen/Alq 3 double layers (device C) showed a trade-off in the electroluminescence characteristics with higher current density and luminance than the device B and better roll-off characteristics of current efficiency than the device A. Electroluminescent spectra of the fabricated devices showed the double emission peaks at 479 nm and 500 nm.

Partly obscured accretion disc model to explain shifted broad Balmer emission lines of active galactic nuclei

We present a new model to explain the appearance of red/blue-shifted broad low-ionization emission lines, especially emission lines in optical band, which is commonly considered as an indicator of radial motion of the line emitting gas in broad emission line regions (BLRs) of Active Galactic Nuclei (AGN). We show that partly obscured disk-like BLRs of dbp emitters (AGN with double-peak broad low-ionization emission lines) can also successfully produce shifted standard Gaussian broad balmer emission lines. Then we calculate two kinds of BH masses for AGN with shifted broad balmer emission lines selected from SDSS. We find that the BH masses calculated from M-sigma relation are systematically larger than virial BH masses for the selected objects, even after the correction of internal reddening effects in BLRs. The smaller virial BH masses than BH masses from M-sigma relation for objects with shifted broad emission lines are coincident with what we expect from the partly obscured accretion disk model. Thus, we provide an optional better model to explain the appearance of shifted broad emission lines, especially for those objects with underestimated virial BH masses.

Synthesis and light-emitting properties of 2-(N-phenyl-α-naphthylamino) and 2-dimesitylboron-7-(N-phenyl-α-naphthylamino)-9,9-diethylfluorene

A fluorescent organic triarylamine with a symmetric structure, 2,7-bis(N-α-naphthyl-phenylamino)-9,9-diethylfluorene (NPAEF) was synthesized using two methods, modified Ullmann coupling and modified palladium-catalyzed amination. An activated copper and a combination of Pd(OAc)2/P(t-Bu)3 and Pd(dba)2/P(t-Bu)3 were selected as catalysts to improve yields of reactions. These synthetic procedures were also successfully applied to an asymmetric 2-dimesitylboron-7-(N-phenyl-α-naphthylamino)-9,9-diethylfluorene (BNPEF). Photoluminescent emission peaks in solid film and in diluted solution of NPAEF were both observed at 461 nm, while the main emission peaks of BNPEF appeared at 422 nm in hexane, and at 480 nm in methanol. The double emission peaks of BNPEF in hexane reflected fine structure in the vibrational state. With an increasing polarity of solvent, the main PL emission peaks were red-shifted and vibrational fine structure disappeared. Additionally, energy levels of NPAEF were investigated and an electroluminescence (EL) device of ITO/PVK:NPAEF/Al was fabricated, which showed a turn-on voltage of 9 V and peaked at 462 nm. The EL spectrum was in good agreement with PL spectrum, which indicated that they were from the same emitting center in the device.

Characterization of asymmetric GaN/InGaN multiple quantum well

AbstractThe microstructure and electronic structure of the asymmetric GaN/InGaN multiple quantum well (MQW) light emitting diodes are characterized by transmission electron microscope (TEM), cathodoluminescence (CL) and capacitance‐voltage (C‐V) measurements. In TEM images, the asymmetric structure of InGaN/GaN MQW are observed as designed with different width of QWs and barriers, and indium content in QWs as well. In high‐resolution TEM images, the InGaN quantum wells and GaN barriers show the same lattice constant, and some degradation can be seen at the bottom of each InGaN QW. There are two emission peaks, 450 and 530 nm in CL spectrum, similar to the ones in electroluminescence spectrum. The double emission peaks are assigned to the irradiative recombination in different InGaN QWs. From the C‐V data, the apparent carrier concentration in the asymmetric MQW is calculated. There are five obvious peaks which are well explained by an energy band scheme of InGaN/GaN MQW. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Photoluminescence characterization of polythiophene films doped with highly functional molecules

Conducting polymer polythiophene (PT) films incorporated with copper phthalocyanine (CuPc) or fullerene C60 or both molecules together were synthesized and characterized by photoluminescence measurements. The hybrid materials were also modified by electrochemically applying positive or negative voltage or by adding the donor molecule tetrathiafulvalene (TTF) or acceptor molecule tetracyanoquinodimethane (TCNQ) into the hybrid films and were investigated by photoluminescence measurements in order to obtain fundamental photoluminescence properties of the hybrid materials. The molecule was injected by electrochemical and diffusion methods. A photoluminescence emission peak was observed at 594 nm in the case of a PT sample doped with CuPc by the diffusion method. Adding C60 molecules to the CuPc diffused PT sample by the diffusion method made the emission peak shift to the higher wavelength at 730 nm, suggesting the molecular interaction between the polymer chain and C60 in the photoluminescence emission process because double emission peaks were observed at 590 and 735 nm in the case of single doping of C60. Electrochemically applying voltages to the films or adding donor molecule TTF and acceptor molecule TCNQ to the polymer hybrid films caused the photoluminescence peak shifts, loss, and enhancement. The present study showed the possibility of control of photoluminescence wavelength of the hybrid films.

Scintillating properties of Pr-doped YAlO3 single crystals grown by the micro-pulling-down method

Pr-doped YAlO3 (0.1, 0.5, 1, 2, 3, 4, 5, and 6 mol % Pr6O11) single crystals were grown by the micro-pulling-down method and their optical and luminescence properties were investigated in the range 80–300 K. Dominant 5d–4f double-peak emission at 254 and 282 nm was observed both in radio-and photoluminescence, and was accompanied by weak 4f–4f luminescence at 495 and 620 nm. The 5d–4f emission shows almost no temperature dependence below 300 K, and achieved radioluminescence intensity is more than 15 times higher than that of Bi4Ge3O12.

Structural phase control of CdSe thin films by metalorganic chemical vapor deposition

Photoluminescence of CdSe thin films under different growth conditions was studied in this paper, and typical double emission peaks were observed at room temperature. Temperature and excitation intensity-dependent photoluminescence studies in combination with X-ray diffraction measurements revealed that the two emission peaks originate from cubic- and hexagonal-phased CdSe, respectively, which indicates that the crystalline phases of CdSe can be controlled by changing the growth conditions in metalorganic chemical vapor deposition process.