Bands Of O2 Research Articles

The luminescence of Eu3+ activated Ba2Mg(BO3)2 phosphors

Phosphors of Eu3+ activated Ba2Mg(BO3)2 were prepared by a high-temperature solid-state reaction technique. The phase purity was characterized by powder X-ray diffraction (XRD). The luminescence properties in the VUV–vis range as well as the decay curves have been investigated. The results demonstrate that the band near 176 nm in the VUV excitation spectra can be ascribed to host-related absorption. The charge-transfer bands (CTBs) of O2− → Eu3+ in Ba2Mg(BO3)2:Eu3+ are at about 231 nm. The emission intensity of the 5D0→7F1 transition (594 nm) is dominant upon excitations at 172 nm or 231 nm (CTB), while that of 5D0→7F2 transition (613 nm) is dominant when excitations are at 395 nm (the 7F0→5L6 transition of Eu3+) or at other f–f transitions.

Atmospheric wave induced O<sub>2</sub> and OH airglow intensity variations: effect of vertical wavelength and damping

Abstract. From nocturnal variations of the airglow O2 (0-1) and OH Meinel (6-2) band emission intensity and the rotational temperature, gravity waves and the damping effect in the MLT region were investigated. The data set was obtained from photometer measurements at Rikubetsu (43.5° N, 143.8° E), Japan, from March 2004 to August 2005. The ratio of the amplitude of oscillation and their phase difference between the two emissions were calculated when simultaneous periodic variations were observed. The ratio showed a linear correlation with the phase difference. The vertical wavelength and damping rate were estimated by using a model calculation carried out by previous works. The results show that the wave damping is significant when the vertical wavelength is shorter than 30–40 km. Krassovsky's parameter η, which represents a ratio between the emission intensity and temperature oscillations, was also calculated. The results show that the η also depends on the damping effect.

Excitation of the oxygen nightglow on the terrestrial planets

A scheme of excitation, quenching, and energy transfer processes in the oxygen nightglow on the Earth, Venus, and Mars has been developed based on the observed nightglow intensities and vertical profiles, measured reaction rate coefficients, and photochemical models of the nighttime atmospheres of the Venus and Mars. The scheme involves improved radiative lifetimes of some band systems, calculated yields of the seven electronic states of O2 in termolecular association, and rate coefficients of seven processes of electronic quenching of the Herzberg states of O2, which are evaluated by fitting to the nightglow observations. Electronic quenching of the vibrationally excited Herzberg states by O2 and N2 in the Earth's nightglow is a quarter of total collisional removal of the O2(A, A′) states and a dominant branch for the O2(c) state. The scheme supports the conclusion by Steadman and Thrush (1994) that the green line is excited by energy transfer from the O2(A3Σu+, v≥6) molecules, and the inferred rate coefficient of this transfer is 1.5×10−11cm3s−1. The O2 bands at 762nm and 1.27μm are excited directly, by quenching of the Herzberg states, and by energy transfer from the O2(5Πg) state. Quenching of the O2 band at 762nm excites the band at 1.27μm as well. Effective yield of the O2(a1Δg) state in termolecular association on Venus and Mars is ∼0.7. Quantitative assessments of all these processes have been made. A possible reaction of O2(c1Σu−)+CO is a very minor branch of recombination of CO2 on Venus and Mars. Night airglow on Mars is calculated for typical conditions of the nighttime atmosphere. The calculated vertical intensity of the O2 band at 1.27μm is 13kR, far below the recently reported detections.

Optical atmospheric extinction over Cerro Paranal

Aims: The present study was conducted to determine the optical extinction curve for Cerro Paranal under typical clear-sky observing conditions, with an accuracy of 0.01 mag/airmass. Methods: The extinction curve of Paranal was obtained through low-resolution spectroscopy of 8 spectrophotometric standard stars observed with FORS1 mounted at the 8.2 m Very Large Telescope, covering a spectral range 3300-8000 A. A total of 600 spectra were collected on more than 40 nights distributed over six months, from October 2008 to March 2009. The average extinction curve was derived using a global fit algorithm, which allowed us to simultaneously combine all the available data. The main atmospheric parameters were retrieved using the LBLRTM radiative transfer code, which was also utilised to study the impact of variability of the main molecular bands of O2, O3, and H2O, and to estimate their column densities. Results: In general, the extinction curve of Paranal appears to conform to those derived for other astronomical sites in the Atacama desert, like La Silla and Cerro Tololo. However, a systematic deficit with respect to the extinction curve derived for Cerro Tololo before the El Chichon eruption is detected below 4000 A. We attribute this downturn to a non standard aerosol composition, probably revealing the presence of volcanic pollutants above the Atacama desert. An analysis of all spectroscopic extinction curves obtained since 1974 shows that the aerosol composition has been evolving during the last 35 years. The persistence of traces of non meteorologic haze suggests the effect of volcanic eruptions, like those of El Chichon and Pinatubo, lasts several decades. The usage of the standard CTIO and La Silla extinction curves implemented in IRAF and MIDAS produce systematic over/under-estimates of the absolute flux.

Neural networks for CO2 profile retrieval from the data of GOSAT/TANSO-FTS

The feasibility of the retrieval of CO2 vertical profiles and its column-averaged concentration by reflected solar radiation measured by the TANSO-FTS sensor onboard the GOSAT satellite is demonstrated. Model spectra in the 0.76-µm O2 band and CO2 bands near 1.6 and 2.06 µm were used to train the neural network for CO2 retrieval. Separate neural networks were developed for each of the four scanning angles; the solar zenith angle was considered as a continuous variable. An accuracy of better than 1 ppm for column-averaged values and better than 4 ppm for the surface CO2 concentration were achieved. A 1: 300 noise level in the spectra was set for all spectral ranges.

Photoluminescence Study of Diffusion and Reactions of 18O-labeled Interstitial Oxygen Molecules in Amorphous SiO2

A photoluminescence (PL) method to evaluate the concentration and isotopic fraction of 18O-labeled oxygen molecules (O2) dissolved in interstitial voids in amorphous SiO2 (a-SiO2) was developed. This method utilizes laser-induced infrared PL bands of interstitial O2 attributed to the transition from the first excited singlet state, in particular, the vibrational sideband coupled to the O-O stretching mode. From the variation of the concentration and isotopic fraction of interstitial O2 with time and temperature of thermal annealing under an 16O2 or 18O2 atmosphere, the diffusion of interstitial O2 as well as the rate of oxygen exchange between interstitial O2 and the Si-O network were examined directly and quantitatively. This observation provides clear experimental evidence that the main oxygen transport mechanism in a-SiO2 is the permeation of interstitial O2.

Experimental Line Parameters of the b1Σg+ ← X3Σg− Band of Oxygen Isotopologues at 760 nm Using Frequency-Stabilized Cavity Ring-Down Spectroscopy

Positions, intensities, self-broadened widths, and collisional narrowing coefficients of the oxygen isotopologues 16O18O, 16O17O, 17O18O, and 18O18O have been measured for the b1 Sigma(g) + <-- X3 Sigma(g) - (0,0) band using frequency-stabilized cavity ring-down spectroscopy. Line positions of 156 P-branch transitions were referenced against the hyperfine components of the 39K D1 (4s 2S1/2 --> 4p 2P1/2) and D2 (4s 2S1/2 --> 4p 2P3/2) transitions, yielding precisions of approximately 0.00005 cm-1 and absolute accuracies of 0.00030 cm-1 or better. New excited b1 Sigma(g) + state molecular constants are reported for all four isotopologues. The measured line intensities of the 16O18O isotopologue are within 2% of the values currently assumed in molecular databases. However, the line intensities of the 16O17O isotopologue show a systematic, J-dependent offset between our results and the databases. Self-broadening half-widths for the various isotopologues are internally consistent to within 2%. This is the first comprehensive study of the line intensities and shapes for the 17O18O or 18O2 isotopologues of the b1Sigma(g) + <-- X3 Sigma(g) - (0,0) band of O2. The 16O2, 16O18O, and 16O17O line parameters for the oxygen A-band have been extensively revised in the HITRAN 2008 database using results from the present study.

Semidiurnal thermal tide in the mesopause region over Yakutia

The study is based on measuring fluctuations of the intensity and rotational temperatures of the molecular emissions of hydroxyl OH(6,2) and the first atmospheric band of oxygen O2(0–1), excited at approximately 87 and 95 km, respectively. The measurements are conducted at Maimaga station (63°N, 129.5°E), located 150 km north of Yakutsk. The semidiurnal tide parameters were obtained using the database compiled from 1999 to 2005. The data obtained from October to March were analyzed. The measurements conducted during 214 nights were used to determine the semidiurnal tide parameters. The wave amplitude at the height of the molecular oxygen emission (∼95 km) is 8 K, which is larger than the amplitude at the height of the hydroxyl emission (∼87 km) by approximately 2 K. Except November, the 12-h oscillation at the height of molecular oxygen excitation leads the oscillation at the height of hydroxyl excitation. On average, the phase is ∼5.7 h at the OH emission height and ∼6.4 h at the O2 emission height. We note that an abrupt increase in the tide amplitude in March at the molecular oxygen height can be related to a seasonal decrease in the so-called “wave” turbopause height.

Seasonal features in the response of the mesopause temperature and emission intensities to solar activity variations

The seasonal dependences of the response of the hydroxyl ((6–2) band) and molecular oxygen O2(b1Σg+) ((0–1) band) emission intensities, temperature, and density indicator in the region of the hydroxyl emission maximum (87 km) to solar activity have been obtained based on the spectral observations of the mesopause emissions at Zvenigorod observatory during 2000–2007. The ratio of the OH (7–3) and (9–4) band intensities, characterizing the behavior of the vibrational temperature, has been used as an indicator of density. It has been established that the response of the studied mesopause characteristics to solar activity is positive in all seasons. In winter the response is maximal in the intensities and temperature and is minimal in the density indicator. The main mechanisms by which solar activity affects the mesopause characteristics have been considered. The behavior of the internal gravity waves with periods of 0.33–7 h depending on solar activity has been studied. It has been noted that these waves become more active at a minimum of the 11-year solar cycle.

Net Emission Coefficients of Radiation in Air and SF6 Thermal Plasmas

Net emission coefficients of radiation were calculated for isothermal plasmas of air and SF6 as a function of the plasma temperature 5,000–30,000 K and the arc radius (0.01–10 cm) at various plasma pressures. Calculations take into account continuum and line radiations, special attention has also been taken to influence of molecular species in case of the air plasmas. It has been found that the molecular bands of O2, N2, N2 +, NO and NO+ have very strong effect on the net emission coefficients at low temperatures (below 10,000 K). In case of SF6, effect of PTFE admixture on the net emission coefficients was also studied. It follows from the calculations that the net emission coefficients vary very little with various admixtures of PTFE. Values of net emission coefficients if SF6 plasma calculated for various spectral regions were compared.

A new source of auroral infrared emission observed by TIMED/SABER

We demonstrate for the first time that O2+ + NO charge transfer produces NO+(v). This mechanism identifies a new source of auroral infrared emission at 4.3 μm, which provides a major step forward in understanding auroral processes and a new context for understanding previously observed auroral enhancements in O2(b1Σg+) and O2(a1Δg) bands. The charge transfer process is identified by comparing physics‐based model simulations with NO+(v) volume emission rates derived from SABER 4.3 μm limb emission measurements.

Summer-time nocturnal wave characteristics in mesospheric OH and O2 airglow emissions

Abstract The mesospheric temperature mapper (MTM) measurements on mesospheric OH (6, 2) and O2 (0, 1) band emissions from Maui, Hawaii during July, 2002 show significant day-to-day variability. The nocturnal variability reveals prominent wave signatures with a periodicity ranging from 6 to 13 h. For better characterization of the nocturnal wave in the data, a Krassovsky’s η (∼|η|e iφ) analysis was carried out. Deduced Krassovsky parameters show significant variability, with ranges of |η| ∼ 1.7–3.9 for the OH data and ∼4.3–13 for the O2 data. The phase values of Krassovsky parameters exhibit larger variability, with variations from approximately −91° to +23° for the OH data and −45° to −10° for the O2 data. Comparison of these values with existing observations and models show large deviations from model values and relatively better agreements with the observed values reported by other investigators. The deduced vertical wavelength from |η| and φ indicates that our data is mostly dominated by upward propagating waves with occasional high values ≥100 km, implying possible evanescent waves.

Energy transfer and enhanced luminescence in metal oxide nanoparticle and rare earth codoped silica

A significant enhancement of photoluminescence from Eu3+ embedded in SiO2 matrix is observed by codoping with wide band-gap In2O3 nanoparticles. The enhanced photoluminescence characteristics are strongly influenced by the postannealing temperature and the In3+ concentration. Synchronous scanning photoluminescence technique was used to understand the excitation and luminescence behavior in codoped silica films. Based on the experimental results, we argue that the enhancement of photoluminescence is associated with the effective energy transfer process from In2O3 nanoparticles to the charge transfer band of O2+–Eu3+ instead of the direct transfer to the rare-earth energy levels.

The temperature of the Venus mesosphere from O2 (aΔg1) airglow observations

We have used near-infrared spectroscopic observations of the Venus nightside taken with the Infrared Imager and Spectrograph 2 (IRIS2) on the Anglo–Australian Telescope to derive temperature maps for the Venus mesosphere at an altitude of ∼95 km. The temperatures are derived from the distribution of rotational line intensities in the O2 (aΔg1) airglow band at 1.27 μm. To obtain reliable temperatures at the relatively low spectral resolution of IRIS2, we have developed a forward modeling approach to handle the blending of individual O2 lines and the telluric absorption in the same O2 band. The technique provides temperature retrievals with accuracy comparable to, or better than that of previous high-spectral resolution determinations. The resulting temperature maps show spatial temperature structure that varies from night to night, as does the intensity distribution. Intensity weighted mean temperatures range from about 181 to 196 K. The temperatures are typically 15–30 K higher than those expected from the Venus International Reference Atmosphere (VIRA) profile. The temperatures fall in regions of low O2 emission rate to values closer to the VIRA levels. Our temperatures are similar to, but slightly lower than those obtained from stellar occultation measurements with SPICAV on Venus Express. We suggest that we are seeing a region of locally enhanced temperature caused by compressional heating in the downwelling gas around the antisolar point.

VUV spectroscopic properties of rare-earth (RE3+ = Eu, Tb, Tm)-doped AZr2(PO4)3 (A+ = Li, Na, K) type phosphate

The excitation spectra of pure and rare-earth (RE3+ = Eu, Tb, Tm)-doped AZr2(PO4)3 (A+ = Li, Na, K) in the vacuum ultraviolet (VUV) regions are investigated. The results indicate that these samples show strong absorption in the VUV range. The band ranging from 130 to 160 nm is due to the absorption band of host lattice or PO4 groups; the band at 160–200 nm is related to the charge transfer (CT) transition of O–Zr. For Eu3+-doped samples, the weak band in the excitation spectra at about 208 nm is related to the CT band of O2−–Eu3+. As for Tb3+-doped samples, the strong band at 225 nm and the weak band at 261 nm in the excitation spectra are assumed to the spin-allowed and spin-forbidden f–d transitions (4f8→ 4f75 d1) of Tb3+. However, there is no obvious band of CT of O2−–Tm3+ in the Tm3+-doped samples.

Formation of I2(B3Π) in the presence of O2(a1Δ)

The mechanism by which I2(B3Π0) is excited in the chemical oxygen-iodine laser was studied by means of emission spectroscopy. Using the intensity of the O2(b1Σ,υ′=0)→O2(X3Σ,υ″=0) band as a reference, I2(B3Π0) relative number densities were assessed by measuring the I2(B3Π0,υ′)→I2(X1Σ,υ″) emission intensities. Vibrationally excited singlet oxygen molecules O2(a1Δ,υ′=1) were detected using infrared emission spectroscopy. The measured relative density of O2(a1Δ,υ′=1) for the conditions of a typical oxygen-iodine laser medium amounted to ∼15% of the total O2(a1Δ) content. Mechanisms for I2(B3Π0) formation were proposed for both the I2 dissociation zone and the region downstream of the dissociation zone. Both pumping mechanisms involved electronically excited molecular iodine I2(A′3Π2u, A3Π1u) as an intermediate. It is proposed that in the dissociation zone the molecular iodine A′3Π2u and A3Π1u states are populated in collisions with vibrationally excited singlet oxygen molecules O2(a1Δ,υ′), whereas in the downstream region of the dissociation zone those intermediate states are populated by the atomic iodine recombination process. I2(B3Π0) is subsequently formed in collisions of I2(A′3Π2u, A3Π1u) with singlet oxygen. We also demonstrated that I2(B3Π0) does not participate measurably in the I2 dissociation process, and that energy transfer from O2(b1Σ) does not excite I2(B3Π0) to a significant degree.

Small‐scale temperature fluctuations associated with gravity waves cause additional radiative cooling of mesopause the region

We present a study of the radiative cooling of the mesosphere and lower thermosphere in the infrared bands of CO2, O3 and H2O due to small‐scale irregular temperature fluctuations caused by gravity waves. These persistent fluctuations are presently not well represented by general circulation models. A statistical model of gravity wave‐induced temperature variations was applied to large‐scale temperature profiles, and the corresponding direct radiative calculations were performed. We show that temperature fluctuations can cause an additional cooling up to 3 K day−1 near the mesopause. The effect is produced mainly by the fundamental 15 μm band of the main CO2 isotope. We found a simple correction depending on the temperature fluctuations variance, which should be added in radiative calculations to the mean temperature profile to account for the additional cooling associated with the unresolved disturbances.

O(1S), OH, and O2(b) airglow layer perturbations due to AGWs and their implied effects on the atmosphere

The O(1S) (green line) night airglow emission in response to atmospheric gravity wave (AGW) perturbations was simulated with a linear, one‐dimensional model. The results were combined with previously modeled O2(b, 0–1) atmospheric band and OH Meinel band emission response (Liu and Swenson, 2003) to derive amplitude and phase relations among multiple airglow layers in response to gravity waves with various intrinsic parameters and damping rates (β). The simulations show that the vertical profile of the standard deviation of the perturbed green line volume emission rate (VER) has a centroid altitude that is 3 km lower and a full‐width‐half‐maximum 2.1 km smaller than the unperturbed VER profile, similar to findings for the OH and O2(b) band layers. Relative phase differences and amplitudes of vertically propagating waves can be deduced from zenith observations of the layers. Airglow weighted responses to waves are related through a cancellation factor (CF) for both layer intensity and temperature. The vertical wavelength can be deduced from relative phase information of three airglow layers separated in altitude. The vertical flux of horizontal momentum associated with gravity waves is deduced from intrinsic wave parameters. Wave damping versus altitude is used to deduce the flux divergence and local accelerations resulting from dissipative waves. The simulations are useful in calculating wave information and wave effects on the atmosphere from multiwavelength, zenith airglow observations.

Electrolytic coloration of oxygen-doped lithium fluoride crystals

Oxygen-doped lithium fluoride crystals were colored electrolytically by using a pointed cathode and a flat anode at various temperatures and electric field strengths, which mainly benefit appropriate coloration temperatures and electric field strengths as well as anode structure of used electrolysis apparatus. Characteristic spectral bands of O2−-Va+ dipoles and O2−-Va+ dipole complexes and magnesium-related F, M, magnesium-perturbed F2+, oxygen-perturbed F2+, F3− color centers were observed in absorption spectra of the colored crystals. Current-time curves for the electrolytic colorations and their relationships with the electrolytic coloration processes were given. Color-center formation in the electrolytic coloration was explained.

Vacuum-ultraviolet absorption of interstitial O2 and H2O molecules in SiO2 glass

Vacuum-ultraviolet (VUV) absorption of O2 and H2O molecules incorporated in interstitial voids in SiO2 glass by thermal annealings was examined. Interactions of the interstitial molecules with the surrounding SiO2 glass network lead to a redshift of the VUV absorption band of interstitial O2, while a blueshift of that of interstitial H2O, both accompanied by an increase in the intensity of the absorption bands. The Coulomb repulsion, London dispersion, and hydrogen bonding are the main interactions responsible for the modification of the VUV absorption bands.