Double-peak Emission Research Articles

Double peak emission in lead halide perovskites by self-absorption

We demonstrate that the often observed double peak emission in lead halide perovskites is caused by an extensive self-absorption effect.

Analysis of spiral structure in the accretion disc of the nova-like cataclysmic variable EC21178–5417

ABSTRACT We present an extensive Doppler tomography study of the eclipsing nova-like EC21178–5417, which exhibits the classic accretion disc signature in the form of double-peak emission lines in its spectrum. Doppler tomograms confirm the presence of a strong, two-armed spiral pattern visible in the majority of the spectral lines studied. This makes EC21178–5417 one of the very few nova-likes that show spiral structure in their discs. We also report night-to-night changes in the position and relative strength of the spiral arms, revealing fluctuations on the conditions in the accretion disc.

The Remarkable Be+sdOB Binary HD 55606. I. Orbital and Stellar Parameters*

Abstract Prompted by peculiar spectroscopic variability observed in SDSS/APOGEE H-band spectra, we monitored the Be star HD 55606 using optical spectroscopy and found that it is an exotic double-lined spectroscopic binary (SB2) consisting of a Be star and a hot, compact companion that is probably an OB subdwarf (sdOB) star. The motion of the sdOB star is traced by its impact on the strong He i lines, observed as radial velocity (V r ) variable, double-peaked emission profiles with narrow central absorption cores. Weak He ii 4686 Å absorption associated with the companion star is detected in most spectra. Use of the emission peaks of low-ionization emission lines to trace the Be star V r and the He i lines to trace the companion star V r yields a circular orbital solution with a 93.8 day period and masses of M Be = 6.2 M ⊙ and M sdOB = 0.9 M ⊙ in the case of i = 80°. HD 55606 exhibits a variety of phase-locked variability, including the development of shell lines twice per orbit. The shell phases coincide with variation in the double emission peak separations, and both forms of variability are likely caused by a two-armed spiral density perturbation in the Be disk. The intensity ratios of the double emission peaks are also phase-locked, possibly indicating heating by the sdOB star of the side of the Be disk facing it. HD 55606 is a new member of the growing sample of Be+sdOB binaries, in which the Be star’s rapid rotation and ability to form a disk can be attributed to past mass-transfer.

Dual-Wavelength InGaAsSb/AlGaAsSb Quantum-Well Light-Emitting Diodes

We have investigated the structural characteristics and the device performance of three-stack InGaAsSb/AlGaAsSb quantum-well (QW) light-emitting diodes (LEDs) grown by using molecular beam epitaxy. The QW LED structure with an 8-nm well thickness had a single peak emission wavelength of 2.06 μm at an injection current of 0.3 A at room temperature. However, the QWLEDs with three different well thicknesses of 5-, 10-, and 15-nm had double peak emission wavelengths of 1.97 and 2.1 μm at an injection current of 1.1 A, which were associated with the radiative recombination in the QW with a 5-nm well thickness and the overlapped emission from the QWs with 10- and 15-nm well thicknesses, respectively.

Investigation on Organic Molecule Additive for Moisture Stability and Defect Passivation via Physisorption in CH3NH3PbI3 Based Perovskite

We investigate the role of n-type organic molecule, bathocuproine (BCP), additive in perovskite semiconductor film based solar cells using first principle calculations and optoelectronic studies. A state-of-art high fill factor of 0.82 and improved open circuit voltage of 0.95 V for CH3NH3PbI3 (MAPI) based perovskite solar cells are achieved in addition with highly improved (more than one order) electroluminescence efficiency. Delayed emission spectroscopy does not show any blue shift peak or double peak emission suggests no structural changes in 3D perovskite. Contact angle studies using water droplet supports BCP is forming a capping layer to boost moisture barrier. Our experimental findings regarding no 2D structure formation has also been supported by first-principles electronic structure calculations based on DFT in MAPI after insertion of BCP. Furthermore, calculations suggest that a physisorption type of interaction has been found in between MAPI and BCP with an average distance of 2.9 Å. These results were found to be in agreement with steady-state and transient photoluminescence studies where an improved PL is observed by using perovskite solution with BCP additive. Chemical analysis and electroluminescence study confirmed the reduction in defect sites by BCP addition. The study suggests that BCP being a small molecule plays an important role in passivating and improving the MAPI film quality and points to an approach toward utilizing other such additives. Furthermore, this approach can be useful for other optoelectronic devices too based on wider bandgap perovskite semiconductors.

The nebular spectra of the transitional Type Ia Supernovae 2007on and 2011iv: broad, multiple components indicate aspherical explosion cores

The nebular-epoch spectrum of the rapidly declining, "transitional" type Ia supernova (SN) 2007on showed double emission peaks, which have been interpreted as indicating that the SN was the result of the direct collision of two white dwarfs. The spectrum can be reproduced using two distinct emission components, one red-shifted and one blue shifted. These components are similar in mass but have slightly different degrees of ionization. They recede from one another at a line-of-sight speed larger than the sum of the combined expansion velocities of their emitting cores, thereby acting as two independent nebulae. While this configuration appears to be consistent with the scenario of two white dwarfs colliding, it may also indicate an off-centre delayed detonation explosion of a near Chandrasekhar-mass white dwarf. In either case, broad emission line widths and a rapidly evolving light curve can be expected for the bolometric luminosity of the SN. This is the case for both SNe 2007on and 2011iv, also a transitional SN Ia which exploded in the same elliptical galaxy, NGC 1404. Although SN 2011iv does not show double-peaked emission line profiles, the width of its emission lines is such that a two-component model yields somewhat better results than a single-component model. Most of the mass ejected is in one component, however, which suggests that SN 2011iv was the result of the off-centre ignition of a Chandrasekhar-mass white dwarf.

Combustion of boron and boron–iron composite particles in different oxidizers

Mechanical milling was used to prepare a composite powder containing 5 wt% of iron in boron. Iron, expected to behave as a catalyst of boron oxidation, was present in the form of nano-sized particles on the agglomerates of primary boron particles. Powders of both the prepared material and as-received boron were burned in different oxidizing environments. The powders were injected in the combustion products of air–acetylene and air–hydrogen flames to expose them respectively to a mixture of CO2, CO and steam as oxidizers. In addition, the powders were fed through a laser beam to be ignited and burned in air. Particle size distributions were obtained for the powders passed through the feeder. Time-resolved optical emission of particles burning in all environments was recorded using photomultipliers filtered at 700 and 800 nm. Additionally, temporally and spectrally resolved emission traces were obtained using a 32-channel spectrometer recording emission in the range of wavelengths of 373–641 nm. The durations of the recorded emission pulses were interpreted as burn times. Statistical distributions of particle burn times and sizes were correlated with each other to obtain the effect of particle size on burn time. Flame temperatures were measured assuming the radiation source behaving as a gray body. Burning boron particles commonly produced double-peak emission pulses, whereas single-peak pulses were produced by the composite boron–iron particles. Both peaks observed in boron particle combustion were assigned to the full-fledged high-temperature reaction unlike the assignment suggested in the earlier research linking the first emission peak with the removal of the boron oxide layer. The emission intensity for the boron–iron composite particles was weaker than that for boron, which is explained by the effect of iron favoring condensed oxidation and suppressing formation of the vapor-phase combustion products, such as boron suboxides. In air, the burn times of boron–iron composite particles were substantially shorter than those of boron. In air–hydrogen flame, boron–iron composites burned slightly faster than boron, while in the air–acetylene flame, there was no clear difference in the burn times for the two materials. The flame temperatures were very similar for the two materials in all oxidizers.

Double-peaked Emission Lines Due to a Radio Outflow in KISSR 1219

Abstract We present the results from 1.5 and 5 GHz phase-referenced VLBA and 1.5 GHz Karl G. Jansky Very Large Array (VLA) observations of the Seyfert 2 galaxy KISSR 1219, which exhibits double-peaked emission lines in its optical spectrum. The VLA and VLBA data reveal a one-sided core-jet structure at roughly the same position angles, providing evidence of an active galactic nucleus outflow. The absence of dual parsec-scale radio cores puts the binary black-hole picture in doubt for the case of KISSR 1219. The high brightness temperatures of the parsec-scale core and jet components (>106 K) are consistent with this interpretation. Doppler boosting with jet speeds of ≳0.55c to ≳0.25c, going from parsec to kiloparsec scales, at a jet inclination ≳50° can explain the jet one-sidedness in this Seyfert 2 galaxy. A blueshifted broad emission line component in [O iii] is also indicative of an outflow in the emission line gas at a velocity of ∼350 km s−1, while the [O i] doublet lines suggest the presence of shock-heated gas. A detailed line ratio study using the MAPPINGS III code further suggests that a shock+precursor model can explain the line ionization data well. Overall, our data suggest that the radio outflow in KISSR 1219 is pushing the emission line clouds, both ahead of the jet and in a lateral direction, giving rise to the double peak emission line spectra.

Growth and scintillation properties of Eu and Ce doped LiSrI3 single crystals

In this study, Eu and Ce doped LiSrI3 single crystals were explored and the scintillation performance was reported at the first time. Eu and Ce doped LiSrI3 single crystals were grown by the Bridgman–Stockbarger method in a quartz ampoule with 3 mm inner diameter. Growth rate was 0.06 mm/min. Circular samples with 1 mm thickness were obtained from the grown crystal. The grown Eu doped LiSrI3 crystal demonstrated Eu2+ 4f–5d emission peak at 420 nm under alpha-ray excitation. In the case of Ce doped one, double emission peaks at 360 and 400 nm were observed. The light yield of the Eu doped LiSrI3 was around 35,000 photon/MeV for 662 keV gamma-ray and 24,000 photon/5.5 MeV for alpha-ray. Energy resolution of the Eu doped LiSrI3 was 5.2%@662 keV. Scintillation decay time of the grown Ce and Eu doped LiSrI3 under 662 keV gamma-ray was 23.8 ns (50%) 212 ns (50%) and 545 ns 100%, respectively.

Green synthesis of nitrogen-doped fluorescent carbon quantum dots for selective detection of iron

ABSTRACTCarbon quantum dots (CQDs) were synthesized by a simple and economic hydrothermal method using Lycium barbarum (LB-CQDs) as precursor. Ammonia was used as a dopant to prepare nitrogen modified LB-CQDs (N-LB-CQDs). The characterizations of atomic force microscope, transmission electron microscopy, X-ray photoelectron spectroscopy showed that N-LB-CQDs were spherical in shape with an average diameter of 2∼5 nm. Its surface was rich in nitrogen-containing groups. The fluorescence spectrophotometer showed that N-LB-CQDs exhibited double peak emission. The two peak positions in photoluminescence were about 462 nm and 512 nm. The as-prepared N-LB-CQDs are high-fluorescent quantum yield and water soluble. In addition, iron selectively results in a strong fluorescence quenching of N-LB-CQDs. Theoretical research results verified that iron reduced energy gap between HOMO and LUMO of N-LB-CQDs greatly, which leads to its emission wavelength shift out of the visible range. Results from the study may shed light on the production of fluorescent and biocompatible CQDs with simple, economic and environmental benign strategy in which Lycium barbarum was used as a carbon source.

Identification of Interesting Objects in Large Spectral Surveys Using Highly Parallelized Machine Learning

AbstractThe current archives of LAMOST multi-object spectrograph contain millions of fully reduced spectra, from which the automatic pipelines have produced catalogues of many parameters of individual objects, including their approximate spectral classification. This is, however, mostly based on the global shape of the whole spectrum and on integral properties of spectra in given bandpasses, namely presence and equivalent width of prominent spectral lines, while for identification of some interesting object types (e.g. Be stars or quasars) the detailed shape of only a few lines is crucial. Here the machine learning is bringing a new methodology capable of improving the reliability of classification of such objects even in boundary cases.We present results of Spark-based semi-supervised machine learning of LAMOST spectra attempting to automatically identify the single and double-peak emission of Hα line typical for Be and B[e] stars. The labelled sample was obtained from archive of 2m Perek telescope at Ondřejov observatory. A simple physical model of spectrograph resolution was used in domain adaptation to LAMOST training domain. The resulting list of candidates contains dozens of Be stars (some are likely yet unknown), but also a bunch of interesting objects resembling spectra of quasars and even blazars, as well as many instrumental artefacts. The verification of a nature of interesting candidates benefited considerably from cross-matching and visualisation in the Virtual Observatory environment.

Spatial emission distribution and carrier recombination dynamics in regularly arrayed InGaN/GaN quantum structure nanocolumns

Emission mechanisms in regularly arrayed InGaN/GaN quantum structures on GaN nanocolumns were investigated, focusing on the spatial emission distribution at the nanocolumn tops and the carrier recombination dynamics. The double-peak emission originated from the dot- and well-like InGaN areas with different In compositions was observed. From the results regarding the spatial emission distribution, we proposed a simple analytical approach to evaluating the carrier recombination dynamics using the rate equations based on the two energy states. The considerable six lifetimes can be uniquely determined from the experimental results. Carrier transfer from the high- to the low-energy state is dominant at high temperatures, producing the increased total emission efficiency of the inner low-energy area. In addition, the internal quantum efficiency should not be simply discussed using only the integrated intensity ratio between low and room temperatures because of the carrier transfer from high- to low-energy states.

A catalog of early-type emission-line stars and Hα line profiles from LAMOST DR2

We present a catalog including 11 204 spectra of 10 436 early-type emission-line stars from LAMOST DR2, among which 9752 early-type emission-line spectra are newly discovered. For these early-type emission-line stars, we discuss the morphological and physical properties of their low-resolution spectra. In this spectral sample, the Hα emission profiles display a wide variety of shapes. Based on the Hα line profiles, these spectra are categorized into five distinct classes: single-peak emission, single-peak emission in absorption, double-peak emission, double-peak emission in absorption, and P-Cygni profiles. To better understand what causes the Hα line profiles, we divide these objects into four types from the perspective of physical classification, which include classical Be stars, Herbig Ae/Be stars, close binaries and spectra contaminated by HΠ regions. The majority of Herbig Ae/Be stars and classical Be stars are identified and separated using a (H-K, K-W1) color-color diagram. We also discuss 31 binary systems that are listed in the SIMBAD on-line catalog and identify 3600 spectra contaminated by HΠ regions after cross-matching with positions in the Dubout-Crillon catalog. A statistical analysis of line profiles versus classifications is then conducted in order to understand the distribution of Hα profiles for each type in our sample. Finally, we also provide a table of 172 spectra with Fe Π emission lines and roughly calculate stellar wind velocities for seven spectra with P-Cygni profiles.

Possible origin of double-peak emission in InGaN quantum wells on m-plane free-standing GaN substrates

A new theoretical model has been proposed to explain the origin of the double-peak emission observed characteristically in m-plane InGaN quantum wells (QWs). Although the emission spectrum with a double-peak structure is generally regarded as evidence of In compositional phase separation or extended crystal defects that generate localized energy states, such crystal irregularities cannot be observed by transmission electron microscopy or three-dimensional atom probe in the QWs. It has been clarified, by our model, that only the slowly decaying tailing of the density of states can cause the double-peak structure. This is consistent with experimental results, and furthermore, the measured temperature and In composition dependences of photoluminescence spectra with the double-peak emission can also be successfully reproduced by theoretical calculation based on our model.

Effect of sol pH on microstructures, optical and magnetic properties of (Co,Fe)-codoped ZnO films synthesized by sol–gel method

Cobalt-iron-codoped ZnO films were synthesized with different precursor sol pHs by a sol–gel method. All the samples possess hexagonal wurtzite structure, with no evidence of secondary phases. The average crystallite size of the samples was in the range of 10–40 nm, accompanying significant differences with the increase of the H+ ion level. The Co/Fe ions are indeed substituted at the Zn2+ site into the ZnO lattice, as shown by XRD and XPS. Strong ultraviolet emission, blue double emission and weak green emission peaks are observed in the photoluminescence spectra of all samples at room temperature. Further studies reveal that the bandgap energy of the ZnO films increases from 3.15 eV (pH = 5) to 3.24 eV (pH = 9). Enhanced room-temperature ferromagnetism is observed for the (Co, Fe)-codoped ZnO films at sol pHs lower than 8. Our work clearly establishes that the origin of room-temperature ferromagnetism in the (Co,Fe)-codoped ZnO films is linked to O vacancies, tunable by the sol pH.

THEMIS Na exosphere observations of Mercury and their correlation with in-situ magnetic field measurements by MESSENGER

The Na exosphere of Mercury is being studied since its discovery in mid ‘80s from Earth-based telescopes, and it has revealed a high dynamics and variability. Although the processes and their relationships characterising the Hermean exosphere generation and dynamics are still not exhaustively understood, there are no doubts on a tight interconnection among the planet's surface, exosphere, intrinsic magnetic field, the solar wind and the Interplanetary Magnetic Field (IMF). In this paper we analyze an extended dataset of images of the exospheric Na emission, collected from 2009 to 2013, by means of the THEMIS ground-based telescope, in order to perform a comprehensive statistical study of the recurrent Na emission patterns, and also their potential relationship with the IMF variability. For this purpose, we take advantage of a subset (years 2011–2013) of contemporary in-situ measurements of the IMF obtained by the MAG instrument on-board the MESSENGER spacecraft. We found that the high latitude double peak is the most common Na emission pattern, supporting the view that the solar wind ion precipitation through the polar cusps has an important role in the generation of the observed Na exospheric configuration. Moreover, the lack of a statistically significant North–South asymmetry seems to disfavor the existence of an asymmetric and/or shifted intrinsic magnetic dipole. By analyzing a subset of quasi-full disk images, we found that the double peak Na emission is typically aligned along the meridian, mostly occurring in the pre-noon sector (53%), about 1/3 close to the noon meridian (36%), whereas only 11% takes place in the post-noon sector. Finally, the comparison with the IMF data seems to indicate that the contribution of the IMF BX component to the magnetic reconnection is generally weak, even if we found a noticeable correlation between positive IMF BX and symmetric double peak pattern. Negative IMF BZ values are usually connected to double peak emission, whereas positive IMF BZ values are more frequently associated to single peaked equatorial Na emission.

Analysis on the structural, vibrational and defect states of chlorine treated polycrystalline cadmium telluride structures grown by e-beam evaporation

Temperature dependent photoluminescence (PL) measurements are performed in order to study the defect states in cadmium chloride treated polycrystalline cadmium telluride (CdTe) thin films grown by e-beam evaporation technique. Three luminescence bands are observed including a double peak emission at 1.577 eV and 1.573 eV corresponding to free electron-to- acceptor transition and a donor–acceptor pair (DAP) transition, respectively, along with a broad peak at 1.45 eV. This broad band emission is related to A-center chlorine based complex and also includes longitudinal (LO) phonon emission lines for CdTe spaced by ∼21 meV. Investigation into grain sizes revealed grains of 0.2 μm for as-grown films and ∼2–3 μm for chlorine activated films shown by atomic force microscopy (AFM). Raman analysis indicates that the films have been grown with excess of Te leading to p-type conductivity in the structure, whereas LO phonon mode of polycrystalline CdTe reveals quasi phonon modes nature.

Effects of pH of the precursor sol on structural and optical properties of Cu-doped ZnO thin films

Cu-doped ZnO thin films deposited on glass substrates by a sol–gel method with sol pH ranging from 6 to 10 were investigated. Characterization of the morphology and microstructures by scanning electron microscopy (SEM) and X-ray diffraction (XRD) revealed that the grain size decreases slightly with an increase of the pH value of the precursor sol. ZnO vary in their orientation along the preferred (002) plane, while the best c-axis orientation occurs in the thin film fabricated from the precursor sol with pH=8.5. X-ray photoelectron spectroscope (XPS) and XRD results indicate that Cu ions are indeed substituted at the Zn2+ site into the ZnO lattice. Strong ultraviolet emission, blue double emission and weak green emission peaks are observed in the photoluminescence spectra of all samples at room temperature. Further studies show that adjusting the pH of the precursor sol can well tune the bandgap from 3.19 to 2.42eV.

INTERGALACTIC MEDIUM EMISSION OBSERVATIONS WITH THE COSMIC WEB IMAGER. I. THE CIRCUM-QSO MEDIUM OF QSO 1549+19, AND EVIDENCE FOR A FILAMENTARY GAS INFLOW

The Palomar Cosmic Web Imager (PCWI), an integral field spectrograph designed to detect and map low surface brightness emission, has obtained imaging spectroscopic maps of Ly-alpha from the circum-QSO medium (CQM) of QSO HS1549+19 at redshift of 2.843. Extensive extended emission is detected from the CQM, consistent with fluorescent and pumped Ly-alpha produced by the ionizing and Ly-alpha continuum of the QSO. Many features present in PCWI spectral images match those detected in narrow-band images. Filamentary structures with narrow line profiles are detected in several cases as long as 250-400 kpc. One of these is centered at a velocity redshifted with respect to the systemic velocity, and displays a spatially collimated and kinematically cold line profile increasing in velocity width approaching the QSO. This suggests that the filament gas is infalling onto the QSO, perhaps in a cold accretion flow. Because of the strong ionizing flux, the neutral column density is low, typically N(HI) is roughly 10E12-10E15/square-cm, and the line center optical depth is also low (typically tau0 is less than 10), insufficient to display well-separated double peak emission characteristic of higher line optical depths. With a simple ionization and cloud model we can very roughly estimate the total gas mass (log M(gas) equal to 12.5 +/- 0.5) and the total mass (log M(tot) equal to 13.3+/- 0.5). We can also calculate a kinematic mass from the total line profile (2x10E13 M(sun)), which agrees with the mass estimated from the gas emission. The intensity-binned spectrum of the CQM shows a progression in kinematic properties consistent with heirarchical structure formation.

Investigating photoinduced charge transfer in double- and single-emission PbS@CdS core@shell quantum dots

We present for the first time detailed investigation of the charge transfer behavior of PbS@CdS core@shell quantum dots (QDs) showing either a single emission peak from the core or intriguing double emission peaks from the core and shell, respectively. A highly non-concentric core@shell structure model was proposed to explain the origin of double emissions from monodisperse QDs. Their charge transfer behavior was investigated by monitoring photoluminescence (PL) intensity variation with the introduction of electron or hole scavengers. It was found that the PL quenching of the PbS core is more efficient than that of the CdS shell, suggesting more efficient charge transfer from the core to scavengers, although the opposite was expected. Further measurements of the PL lifetime followed by wave function calculations disclosed that the time scale is the critical factor explaining the more efficient charge transfer from the core than from the shell. The charge transfer behavior was also examined on a series of single-emission core@shell QDs with either different core sizes or different shell thicknesses and dominant factors were identified. Towards photovoltaic applications, these PbS@CdS QDs were attached onto multi-walled carbon nanotubes (MWCNTs) and their charge transfer behavior was compared with that in the PbS-QD/MWCNT system. Results demonstrate that although the CdS shell serves as an electron transfer barrier, the electrons excited in the PbS cores can still be transferred into the MWCNTs efficiently when the shell thickness is ∼0.7 nm. Considering their higher stability, these core@shell QDs are very promising for the development of highly efficient QD-based photovoltaic devices.