Green Line Emission Research Articles

Multiple Airglow Chemistry approach for atomic oxygen retrievals on the basis of in situ nightglow emissions

Electronically excited states of molecular and atomic oxygen (O2 and O) are coupled with each other as well as with the ground states of O2 and O in the Multiple Airglow Chemistry (MAC) model representing the oxygen airglow and the oxygen photochemistry in the upper Mesosphere and Lower Thermosphere region. The MAC model couples seven O2 and three O states and was developed on the basis of insitu measurements from the ETON (Energy Transfer in the Oxygen Nightglow) campaign employed to tune rate values of unknown or poorly constrained processes. The same rate values are applied in the MAC model verified and validated on the basis of the insitu measurements obtained during the WADIS-2 (WAve propagation and DISsipation in the middle atmosphere), the WAVE2000 (WAVes in airglow structures Experiment, 2000) and WAVE2004 campaigns. Data sets measured using devices aboard the WADIS-2 rocket are considered to be self-consistent because the MAC retrievals of a concentration profile of O in the ground state ([O(3P)]) can be based on these data sets only. The measuring sites of the insitu data sets from the WAVE2000 and WAVE2004 campaigns are collocated with those of remotely obtained data sets, and these data sets are combined for the MAC retrievals. O2 precursors responsible for the oxygen green line emission, emissions in the Atmospheric band and the Infrared Atmospheric band are identified and confirmed by calculations with the validated MAC model.

E‐POP and Red Line Optical Observations of Alfvénic Auroras

AbstractSuprathermal electron bursts (STEBs), characterized by a board energy spectrum and a field‐aligned pitch angle distribution, have been well recognized to be associated with electron acceleration by inertial Alfvén waves and are thus conventionally termed as “Alfvénic aurora.” In this study, we report joint Enhanced‐Polar‐Outflow‐Probe (e‐POP) and ground‐based optical observations of Alfvénic auroras. In particular, we highlight the prominence of 630‐nm red line emissions under low‐energy Alfvénic auroral precipitation. During the event interval, e‐POP traverses two arcs. One bright arc dominated by green line emissions is clearly seen by all optical instruments; it is embedded in upward field‐aligned currents (FACs) yet leaves little imprint on the e‐POP suprathermal electron imager (SEI), likely due to that the precipitation is well above the upper energy limit of SEI. On the other hand, there is a red line arc that is pronounced only in 630‐nm images. Such a red‐line‐only arc is located in a transition from large‐scale upward FACs to downward FACs and is associated with a prominent STEB structure detected by e‐POP SEI. The STEB features an inverse energy time dispersion, namely, that lower‐energy electrons are seen earlier while higher‐energy electrons appear later. The red‐line‐only arc and its separation from the green line arc evolve in a repeatable fashion, each stemming from a poleward auroral intensification (PAI) propagated from higher latitudes. Following each poleward auroral intensification the green line arc progressively moved southward, while the red‐line‐only arc is quasi‐stationary and stayed relatively stable in latitude. We propose tentative interpretations of the above features based upon stationary inertial Alfvén waves.

A Search for High-Frequency Coronal Brightness Variations in the 21 August 2017 Total Solar Eclipse

We report on a search for short-period intensity variations in the green-line (Fe xiv 530.3 nm) emission from the solar corona during the 21 August 2017 total eclipse viewed from Idaho in the United States. Our experiment was performed with a much more sensitive detection system, and with better spatial resolution, than on previous occasions (1999 and 2001 eclipses), allowing fine details of quiet coronal loops and an active-region loop system to be seen. A guided 200-mm-aperture Schmidt–Cassegrain telescope was used with a state-of-the-art CCD camera having 16-bit intensity discrimination and a field-of-view (0.43^{ circ } times 0.43^{circ }) that encompassed approximately one third of the visible corona. The camera pixel size was 1.55 arcseconds, while the seeing during the eclipse enabled features of {approx}, 2 arcseconds (1450 km on the Sun) to be resolved. A total of 429 images were recorded during a 122.9 second portion of the totality at a frame rate of 3.49~mbox{s}^{-1}. In the analysis, we searched particularly for short-period intensity oscillations and travelling waves, since theory predicts fast-mode magneto-hydrodynamic (MHD) waves with short periods may be important in quiet coronal and active-region heating. Allowing first for various instrumental and photometric effects, we used a wavelet technique to search for periodicities in some 404mbox{,}000 pixels in the frequency range 0.5,mbox{--},1.6mbox{ Hz} (periods 2 seconds to 0.6 seconds). We also searched for travelling waves along some 65 coronal structures. However, we found no statistically significant evidence in either. This negative result considerably refines the limit that we obtained from our previous analyses, and it indicates that future searches for short-period coronal waves may be better directed towards Doppler shifts as well as intensity oscillations.

Transient Dimming of the Bright Fe xiv Emission Region in the Solar Corona of the 21 August 2017 Total Solar Eclipse

During the 21 August 2017 total solar eclipse the corona was observed through a narrowband filter centered at the Fe xiv green emission line at a cadence of 30 frames/s. A bright region on the east limb was observed to dim during the 2 m 35 s totality. Details of the temporal behavior of this region are reported. The likely association of the dimming with a coronal mass ejection (CME) in progress during the eclipse or the small sunspot group with coronal loops near the east limb is discussed.

Blue-green light-emitting diode with patterned electrode: Spectral analysis

Two step decomposition procedure was developed and implemented to analyze experimentally measured EL-spectra of light-emitting diode (LED) with mesh-like top electrode and two sets of InGaN/GaN quantum wells (QWs) for blue and green emissions. At a first step EL-spectra were decomposed into basic Gaussian functions (GFs) for blue, green, and violet emission lines. Then each of the basic GFs was decomposed into the secondary GFs which give reasonable ground to relate broadening of EL-spectrum to the position dependent compensation of quantum-confined Stark effect (QCSE) in the InGaN/GaN QWs. Metal strips prevent from extraction a portion of light not only with larger intensity but also with shorter wavelength comparing to those for the light extracted from the uncovered active region. Such a “cut-off” manifests itself in longer central peak wavelengths of the basic blue and green GFs obtained by EL-spectrum decomposition comparing to the emission spectra of blue and green QWs. Analysis of basic GFs allowed to evaluate quantitatively splitting of the injected charge carriers between blue and green QWs and the third source of violet emission. This can be useful in optimization-oriented modeling of the LED's performance.

Synthesis, structure and optical properties of erbium-doped lithium barium phosphate

Li2BaP2O7 activated with Er3+ ions was prepared by the classic ceramic method and characterized by X-ray diffraction technique, IR, Raman and photoluminescence (PL) spectroscopies. The Li2BaP2O7: Er phosphors exhibited a monoclinic single phase structure with C2/c space group. A green and red emission lines dominate the spectrum upon excitation at 400 nm. The CIE-coordinate (x = 0.308, y = 0.512) were found in green light. Free ion parameters of the Er3+ ions in Li2BaP2O7 and the Judd–Ofelt parameters were calculated and they were used to explore the radiative parameters such as transition probability (AT), and branching ratios (β) related to the Er3+ emission transitions. The calculated 4S3/2 radiative life time around 0.198 ms is compared with the experimental value. The calculated quantum efficiency is about 42%. Li2BaP2O7: Er can be considered as a novel green phosphor.

Numerical model and procedure for spectral analysis of light-emitting diode with patterned electrode

Two-step decomposition procedure was developed and implemented to analyze experimentally measured electroluminescence (EL) spectra of light-emitting diode with two sets of InGaN/GaN quantum wells (QWs) for blue and green emission and mesh-like top electrode. At a first step EL-spectra were decomposed into basic Gaussian functions (GFs) for blue and green emission lines. Then each of the basic GFs was decomposed into the set of secondary GFs which give reasonable ground to relate broadening of EL-spectrum to position-dependent compensation of quantum-confined Stark effect(QCSE) in the InGaN/GaN QWs. Using basic GFs it was demonstrated how injected current is splitted between green and blue QWs depending on its value.

Spatio-Temporal Evolution and North–South Asymmetry of Quasi-Biennial Oscillations in the Coronal Fe xiv Emission

In this work, we apply multichannel singular spectrum analysis (MSSA), a data-adaptive, multivariate, non-parametric technique that simultaneously exploits the spatial and temporal correlations of the input data to extract common modes of variability, to investigate the intermediate quasi-periodicities of the Fe XIV green coronal emission line at 530.3 nm for the period between 1944 and 2008. Our analysis reveals several significant mid-term periodicities in a range from about one to four years that are consistent with the so-called quasi-biennial oscillations (QBOs), which have been detected by several authors using different data sets and analysis methods. These QBOs display amplitudes varying significantly with time and latitude over the six solar cycles (18 to 23) covered by this study. A clear North-South asymmetry is detected both in their intensity and period distribution, with a net predominance of spectral power in the active-region belt of the northern hemisphere. On the other hand, while the QBOs with periods > 1.7 years are particularly intense around the polar regions and therefore related to the global magnetic field, the ones with shorter periods are mainly generated at mid-latitudes, in correspondence with the emergence of active regions. Our findings indicate that the North-South asymmetry manifested in the uneven latitudinal distribution of QBOs is a fundamental, albeit puzzling, characteristic of solar activity.

Preparation and cathodoluminescence characteristics of rare earth activated BaAl2O4 phosphors

Undoped and Pr, Sm and Tb activated BaAl2O4 phosphors have been synthesized by solid state reaction method and combustion method. The structure and morphological observation of the phosphor samples were monitored by X-ray powder diffraction (XRD) and environmental scanning electron microscope (ESEM) coupled to an energy dispersive X-ray spectrometer (EDS). The all diffraction peaks are well assigned to standard data card (PDF♯17–306). Emission properties of the samples were explored using light emission induced by an electron beam (i.e cathodoluminescence, CL) at room temperature (RT). Undoped BaAl2O4 sample exhibits a broad defect emission from 300 to 500 nm from the aluminate defect centres. CL spectra recorded at room temperature display that the as-prepared BaAl2O4:Ln (Ln=Pr, Sm and Tb) phosphors exhibit different luminescence colors coming from different rare earth activator ions. The transition 4G5/2 → 6H7/2 located at 606 and 610 nm for Sm3+ can occur as hypersensitive transition having the selection rule ΔJ = ± 1. For the Tb3+ doped samples, they exhibit D45 green line emissions. The proposed luminescent mechanisms of all doped rare earth ions are also discussed.

Multivariate analysis of intermediate periodicities of the green corona

AbstractSolar activity is observed to fluctuate with time, undergoing a wide range of periodicities from minutes up to thousands of years as evinced from proxies based on cosmogenic isotopes. In this work, we apply Multichannel Singular Spectrum Analysis (MSSA), a data-adaptive, multivariate technique that simultaneously exploits the spatial and temporal correlations of the input data to extract common modes of variability to investigate the intermediate quasi-periodicities of the green coronal emission line at 530.3 nm for the period between 1944 and 2008. A preliminary MSSA analysis confirms the presence of significant quasi-biennial oscillations in the data with amplitude varying significantly with time and latitude. On the other hand, a clear North-South asymmetry is observed both in their intensity and period distribution.

Green up-conversion luminescence of erbium-doped oxyfluoride germanate fiber under continuous-wave laser-diode excitation

Up-conversion luminescence of Er3+-doped oxyfluoride germanate optical fiber is observed under laser-diode excitation. The enhanced green emission line is due to 2H11/2,4S3/2 → 4I15/2 transition of Er3+. The integrated luminescence intensity related to 2H11/2,4S3/2 → 4I15/2 (green) and 4F9/2 → 4I15/2 (red) transitions of Er3+ is reduced with increasing temperature. Several spectroscopic parameters of Er3+ ions in optical fibers were determined. The spectral linewidth is reduced, whereas the maximum of emission peak is shifted to longer wavelengths with increasing fiber length.

Effect of geomagnetic storm conditions on the equatorial ionization anomaly and equatorial temperature anomaly

The effect of the geomagnetic storm on the equatorial ionization anomaly (EIA) and equatorial temperature anomaly (ETA) has been studied using the atomic oxygen dayglow emissions at 577.7 nm (OI 557.7 nm) and 732.0 nm (OII 732.0 nm). For the purpose of this study, four intense geomagnetic storms during the ascending phase of solar cycle 24 have been considered. This study is primarily based on the results obtained using photochemical models with necessary inputs from theoretical studies and experimental observations. The latest reaction rate coefficients, quantum yields and the corresponding cross-sections have also been incorporated in these models. The volume emission rate of airglow emissions has been calculated using the neutral densities from NRLMSISE-00 and charged densities from IRI-2012 model. The modeled volume emission rate (VER) for OI 557.7 nm shows a positive correlation with the Dst index at 150 km and negative correlation with Dst at 250 and 280 km altitudes. Latitudinal profile of the greenline emission rate at different altitudes show a distinct behaviour similar to what has been observed in EIA with crests on either sides of the equator. The EIA crests are found to show poleward movement in the higher altitude regions. The volume emission rate of 732.0 nm emission shows a strong enhancement during the main phase of the storm. The changes observed in the airglow emission rates are explained with the help of variations induced in neutral densities and parameters related to EIA and ETA. The latitudinal variation of 732.0 nm emission rate is correlated to the variability in EIA during the storm period.

Precursors of an upcoming solar cycle at high latitudes from coronal green line data

After reviewing potential early indicators of an upcoming solar cycle at high latitudes, we focus attention on the rush–to-the-poles (RTTP) phenomenon in coronal green line emission. Considering various correlations between properties of the RTTP with the upcoming solar cycle we find a correlation between the rate of the RTTP and the time delay until the maximum of the next solar cycle. On the basis of this correlation and the known internal regularities of the sunspot number series we predict that, following a minimum in 2019, cycle 25 will peak in late 2024 at an amplitude of about 130 (in terms of smoothed monthly revised sunspot numbers). This slightly exceeds the amplitude of cycle 24 but it would still make cycle 25 a fairly weak cycle.

Polar Thermospheric Winds and Temperature Observed by Fabry‐Perot Interferometer at Jang Bogo Station, Antarctica

AbstractUpper atmospheric neutral winds and temperature have been observed by the Fabry‐Perot interferometer (FPI) which was installed at Jang Bogo Station (JBS), Antarctica, in 2014. Since JBS is mostly located within the polar cap region, the observed thermospheric winds at 250 km show strong diurnal variations with notable antisunward motions due to the effects of plasma convection. The winds at 87 km, on the other hand, show semidiurnal variations due to the lower atmospheric tidal effects. We found that the winds from green line emission show largely diurnal variations, unlike the other independent observations, which might be due to the auroral contamination. The horizontal wind model 2014 winds at 250 km show reasonable agreement with FPI winds, while large discrepancies exist at 87 km in terms of seasonal variations. There is a distinctive asymmetric seasonal variation of the thermospheric zonal wind in the dusk and dawn sectors. FPI temperatures at 250 km show a fairly close correlation with Kp index, especially in 2015 when the geomagnetic activity is stronger. However, the temperatures at 87 km are mostly independent on Kp index. Finally, during the intense geomagnetic storm, thermospheric winds and temperature are significantly disturbed and Thermosphere Ionosphere Electrodynamics General Circulation Model simulations are in surprisingly good agreement with observation for winds but the temperatures are significantly underestimated during the whole storm period.

Luminescence characteristic of RE (RE = Pr, Sm, Eu, Tb, Dy) and energy levels of lanthanide ions in Gd5Si3O12N

Polycrystalline Gd5Si3O12N: RE (RE = Pr, Sm, Eu, Tb and Dy) phosphors have been synthesized via a solid-state reaction method at high temperature, and their photoluminescence properties were studied. The absorption peak at about 230 nm is attributed to the host absorption. For the Pr3+-doped sample, the typical excitation lines located at 273 nm originating from the 8S7/2 → 6IJ (J = 5/2, 7/2) transitions of the Gd3+ ions were observed in the excitation spectra. Upon excitation at 227 nm UV light, the 4f15d → 4f2 emission band (350–450 nm) and typical 4f2 → 4f2 emission lines (450–700 nm) assigned to Pr3+ were observed. The Sm3+-doped sample exhibits a bright red emission owing to the 4G5/2 → 6HJ (J = 5/2, 7/2 and 9/2) transitions. However, the charge transfer band of Sm3+ was not observed in the excitation spectrum. There is a broad band from 200 to 350 nm originating from the charge transfer transition (CT) of the Eu3+ (O2−/N3− → Eu3+) in the excitation spectra, and the strongest peak in the emission spectra located at 615 nm is due to the electric-dipole 5D0 → 7F2 transition of Eu3+. For the Tb3+-doped sample, it shows 5D3 →7FJ (J = 5, 4, 3, 2) blue line emissions and 5D4 → 7FJ (J = 6, 5, 4, 3) green line emissions under the excitation of Tb3+. The Dy3+-activated sample upon excitation at 349 and 386 nm UV light shows blue-green and orange-red emission lines originating from 4F9/2 → 6HJ (J = 15/2, 13/2) transitions. In addition, the energy transfer from the host lattice to the luminescence activators (i.e. Pr3+, Sm3+, Eu3+, Tb3+, Dy3+) has been confirmed. In addition, the energy level diagram including the 4f and 5d energy levels of all Ln2+ and Ln3+ ions relative to the valence and conduction band of Gd5Si3O12N were constructed and discussed.

On the importance of an atmospheric reference model: A case study on gravity wave-airglow interactions

The atmospheric reference model utilized in an airglow numerical study is important since airglow emissions depend on the number density of the light-emitting species. In this study, we employ 2-dimensional, nonlinear, time-dependent numerical models, Multiple Airglow Chemistry Dynamics (MACD) and OH Chemistry Dynamics (OHCD), that use the MSISE-90, NRLMSISE-00, and Garcia and Solomon (GS) model data as atmospheric reference models, to investigate gravity wave-induced airglow variations for the OH(8,3) airglow, O2(0,1) atmospheric band, and O(1S) greenline emissions in the Mesosphere and Lower Thermosphere (MLT) region. Our results show that the OHCD-00 produces the largest wave-induced OH(8,3) airglow intensity variation (∼34%), followed by the OHCD-90 (∼30%), then by the OHCD (∼22%). For O(1S) greenline, the MACD produces the largest wave-induced variation (∼33%), followed by the MACD-90 (∼28%), then by MACD-00 (∼26%). As for O2(0,1) atmospheric band, the MACD produces the largest wave-induced variation (∼31%), followed by the MACD-90 and MACD-00 (∼29%). Our study illustrates the importance and the need for a good atmospheric reference model that can accurately represent the atmosphere.

A study of energy transfer phenomenon leading to photon up-conversion in Ho3+:Yb3+:CaF2 crystalline powders and its temperature sensing properties

When Ho3+:Yb3+:CaF2 crystalline powders prepared by combustion synthesis were exposed to near-infrared (λ ∼ 975 nm) radiation, intense photon up-conversion (UC) was observed at the visible with emission bands peaked at ∼ 545, ∼650 and ∼750 nm identified as 4f-4f transitions from higher levels (5F4, 5S2) and 5F5 to lower levels 5I8 and 5I7 of Ho3+. The emission bands at the green and red, in particular, have been demonstrated to be useful for temperature sensing based on luminescence intensity ratio technique. However, no model is available in literature to explain the change of the electronic populations of states (5F4, 5S2) and 5F5 with temperature. The UC phenomenon was studied from both theoretical and experimental points of view. A rate equation model with temperature dependent parameters for Ho3+ and Yb3+ electronic populations considering a high sensitization of Ho3+ ions by Yb3+ ions was used. High Yb3+ → Ho3+ energy transfer efficiency was found (∼88% at room temperature). The change with temperature predicted by the model for the luminescence intensity ratio of the UC green and red emission lines agrees well with the experimental data.

Highly Efficient Green-Emitting Phosphors Ba2Y5B5O17 with Low Thermal Quenching Due to Fast Energy Transfer from Ce3+ to Tb3.

This paper demonstrates a highly thermally stable and efficient green-emitting Ba2Y5B5O17:Ce3+, Tb3+ phosphor prepared by high-temperature solid-state reaction. The phosphor exhibits a blue emission band of Ce3+ and green emission lines of Tb3+ upon Ce3+ excitation in the near-UV spectral region. The effect of Ce3+ to Tb3+ energy transfer on blue to green emission color tuning and on luminescence thermal stability is studied in the samples codoped with 1% Ce3+ and various concentrations (0-40%) of Tb3+. The green emission of Tb3+ upon Ce3+ excitation at 150 °C can keep, on average, 92% of its intensity at room temperature, with the best one showing no intensity decreasing up to 210 °C for 30% Tb3+. Meanwhile, Ce3+ emission intensity only keeps 42% on average at 150 °C. The high thermal stability of the green emission is attributed to suppression of Ce3+ thermal de-excitation through fast energy transfer to Tb3+, which in the green-emitting excited states is highly thermally stable such that no lifetime shortening is observed with raising temperature to 210 °C. The predominant green emission is observed for Tb3+ concentration of at least 10% due to efficient energy transfer with the transfer efficiency approaching 100% for 40% Tb3+. The internal and external quantum yield of the sample with Tb3+ concentration of 20% can be as high as 76% and 55%, respectively. The green phosphor, thus, shows attractive performance for near-UV-based white-light-emitting diodes applications.

Photoluminescence properties and energy level of RE (RE = Pr, Sm, Tb, Er, Dy) in Y4Si2O7N2

Abstract RE 3+ ( RE = Pr, Sm, Tb, Er, Dy)-activated Y 4 Si 2 O 7 N 2 samples were prepared by a solid-state reaction method at high temperature, and their photoluminescence properties were investigated. The absorption band located at about 250 nm is attributed to the host absorption. The 5 d bands of Pr 3+ and Tb 3+ are at rather low energy in Y 4 Si 2 O 7 N 2 compared to oxide. The direct Pr 3+ 4 f 2 → 4 f 1 5 d 1 excitation at 275 nm leads to typical 4 f 2 → 4 f 2 line emissions (450–700 nm) and strong 4 f 1 5 d 1 → 4 f 2 broad band emission (300–450 nm), respectively. The charge transfer (N 3− → Sm 3+ ) band of Sm 3+ was observed at a somewhat lower energy of 4.68 eV compared to oxide, and Sm 3+ -activated sample shows a bright red emission originating from 4 G 5/2 → 6 H J ( J = 5/2, 7/2 and 9/2) transitions. For Tb 3+ -doped sample, the direct Tb 3+ 4 f 8 → 4 f 7 5 d 1 excitation leads to 5 D 3 → 7 F J ( J = 6, 5, 4, 3) (blue) and 5 D 4 → 7 F J ( J = 6, 5, 4, 3) (green) line emissions, the cross-relaxation depended on Tb concentration has happened. The incorporation of Er 3+ (or Dy 3+ ) into Y 4 Si 2 O 7 N 2 resulted in a typical Er 3+ (or Dy 3+ ) f - f line absorptions and emissions. Moreover, the energy transfer from the host lattice to the luminescent activators (Pr 3+ , Tb 3+ and Sm 3+ ) is observed. The energy level diagram containing the position of 4 f and 5 d energy levels of all Ln 2+ and Ln 3+ ions relative to the valence and conduction band of Y 4 Si 2 O 7 N 2 has been established and studied based on the data presented in this work, and further provides a platform for studying the photoluminescence properties as well as the valence stability of the lanthanide ions.

Blue-green InGaN/GaN light-emitting diode with mesh-like top metal electrode

Light-emitting diodes (LEDs) with blue-green dual-wavelength emission and top metal electrode patterned as a mesh were fabricated using InGaN/GaN material system and tested. In pulsed voltage supply mode an increase in injected current resulted in electroluminescence (EL) with equal peak intensities of blue and green emission lines and shallow trough between them. These features of the LED EL-spectrum can be attributed to the effect of the mesh-like patterning of the top electrode.Meshed electrode promotes the injection of current spatially nonuniform along the planes of the quantum well (QWs) which results not only in spatial nonuniformity of the intensity of generated light but also may contribute to position-dependent compensation of Quantum-confined Stark effect (QCSE) resulting in blue shift of EL in the QWs. The observed phenomenon can be used to control or engineer the EL spectra of dual-wavelength LEDs by electrode patterning.