Afterglow Characteristics Research Articles

Effects of Eu<sup>2+</sup>, Dy<sup>3+</sup> Contents and Particle Sizes on the Luminescent Properties of SrAl<sub>2</sub>O<sub>4</sub> Phosphor by the Sol-Gel Process

A green emitting SrAl2O4:Eu2+, Dy3+ phosphor with high brightness and long afterglow was synthesized by the sol-gel method. SrAl2O4: Eu2+, Dy3+ phosphor exhibited broad band extending from 450 to 650 nm and maximum emission spectra peaking at 520 nm. Three excited levels existed, two shoulders were observed at 270 and 330 nm in addition to the maximum at 360 nm on the excitation spectrum. After the removal of excitation light, the excellent after-glow characteristic of the phosphorescence was obtained as a result of low decay time, although the after-glow intensities of phosphor varied exponentially with the time.

Multiwavelength Analysis of the Intriguing GRB 061126: The Reverse Shock Scenario and Magnetization

We present a detailed study of the prompt and afterglow emission from Swift GRB 061126 using BAT, XRT, UVOT data and multicolor optical imaging from 10 ground-based telescopes. GRB 061126 was a long burst (T90 = 191 s) with four overlapping peaks in its γ-ray light curve. The X-ray afterglow, observed from 26 minutes to 20 days after the burst, shows a simple power-law decay with αX = 1.290 ± 0.008. Optical observations presented here cover the time range from 258 s (Faulkes Telescope North) to 15 days (Gemini North) after the burst; the decay rate of the optical afterglow shows a steep-to-shallow transition (from α1 = 1.48 ± 0.06 to α2 = 0.88 ± 0.03) approximately 13 minutes after the burst. We suggest the early, steep component is due to a reverse shock and show that the magnetic energy density in the ejecta, expressed as a fraction of the equipartition value, is a few 10 times larger than in the forward shock in the early afterglow phase. The ejecta might be endowed with primordial magnetic fields at the central engine. The optical light curve implies a late-time break at about 1.5 days after the burst, while there is no evidence of the simultaneous break in the X-ray light curve. We model the broadband emission and show that some afterglow characteristics (the steeper decay in X-ray and the shallow spectral index from optical to X-ray) are difficult to explain in the framework of the standard fireball model. This might imply that the X-ray afterglow is due to an additional emission process, such as late-time central engine activity rather than blast-wave shock emission. The possible chromatic break at 1.5 days after the burst would give support to the additional emission scenario.

Effects of non-stoichiometry and substitution on photoluminescence and afterglow luminescence of Sr 4Al 14O 25:Eu 2+, Dy 3+ phosphor

The effects of nonstoichiometry and cationic substitution on photoluminescence and afterglow characteristics of strontium aluminate phosphor (Sr 4Al 14O 25:Eu 2+, Dy 3+) were investigated. Photoluminescence intensity of both the strontium-deficit and -rich phosphors was enhanced, but no definite correlation was observed between the afterglow intensity and non-stoichiometry. The photoluminescence emission maxima were either blue or green shifted in case of non-stoichiometric phosphors, whereas the afterglow emission maxima were not affected by the non-stoichiometry. Substitution of strontium by calcium resulted in white afterglow emission at higher calcium concentration. The emission centers in case of photoluminescence and afterglow emission appear to be different. Addition of silver significantly enhanced the afterglow intensity due to increased trap density.

A Novel Synthesis of Alkaline Earth Silicate Phosphor Sr3MgSi2O8:Eu2+,Dy3+

AbstractA novel method for synthesizing long afterglow silicate phosphor Sr3MgSi2O8:Eu2+,Dy3+using TEOS and inorganic powders as reactants was reported. Acetic acid as a catalyzer controlled the hydrolysis of TEOS by adjusting pH value of the system. The morphologies of precursor were characterized by transmission electron microscope (TEM). The structure and optical properties of the phosphor powders were systematically investigated by means of X‐ray diffraction and spectrofluorometry. TEM images have reflected the core‐shell structure and quasi‐spherical morphology of the precursor particles. It was found that the single‐phase Sr3MgSi2O8 crystalline structures were obtained at 1050 and 1250 °C for the samples prepared with the nano‐coating method and the solid state reaction, respectively. The emission intensities of the phosphors prepared by the present method were higher than those by the conventional process. Also, the afterglow characteristic was better than that prepared by solid‐state reaction in the comparable condition.

Battery-Independent Emergency Illumination with RGB Phosphors

Acrylic resins that emit red, green, or blue (RGB) phosphorescence were fabricated. Mixtures of an organic dye and green phosphor created bright afterglow emission in the spectral region from yellow to red, which was difficult to attain with conventional red phosphors. Rhodamine and kiton were suitable for converting green phosphorescence to orange or red fluorescence. The resins continued to glow in darkness for longer than 3 hours after an excitation lamp was turned off. This long afterglow characteristic of the current dye phosphor mixtures was in remarkable contrast with the fast phosphorescence decay of the conventional red phosphors (10-20 mm). These red afterglow resins improve visibility of emergency signs, and realize warm-colored illumination that provides a sense of security in darkness

Synthesis and luminescence properties of Sr 3MgSi 2O 8:Eu 2+,Dy 3+ by a novel silica-nanocoating method

This paper report a novel method for synthesizing long afterglow silicate phosphor Sr 3MgSi 2O 8:Eu 2+,Dy 3+ using TEOS and inorganic powders as reactants. Acetic acid as a catalyzer controlled the hydrolysis of TEOS by adjusting pH value of the system. The morphologies of precursor were characterized by transmission electron microscope (TEM). The structure and optical properties of the phosphor powders were systematically investigated by means of X-ray diffraction and spectrofluorometer. TEM images had reflected the core-shell structure and quasi-spherical morphology of the precursor particles. It found that the single-phase Sr 3MgSi 2O 8 crystalline structures were obtained at 1050 and 1250 °C for the samples prepared with the nano-coating method and the solid-state reaction, respectively. The emission intensities were higher by the present method. Also, the afterglow characteristic was better than that prepared by solid-state reaction in the comparable condition.

X-ray flare in XRF 050406: evidence for prolonged engine activity

We present observations of XRF 050406, the first burst detected by Swift showing a flare in its X-ray light curve. During this flare, which peaks at t_peak ~210s after the BAT trigger, a flux variation of (delta F)/F~6 in a very short time (delta t)/t_peak<<1 was observed. Its measured fluence in the 0.2-10 keV band was ~1.4x10^-8 erg cm^-2, which corresponds to 1-15% of the prompt fluence. We present indications of spectral variations during the flare. We argue that the producing mechanism is late internal shocks, which implies that the central engine is still active at 210s, though with a reduced power with respect to the prompt emission. The X-ray light curve flattens to a very shallow slope with decay index of ~0.5 after ~4400s, which also supports continued central engine activity at late times. This burst is classified as an X-ray flash, with a relatively low fluence (~10^-7 erg cm^-2 in the 15-350 keV band, E_iso~10^51 erg), a soft spectrum (photon index 2.65), no significant flux above ~50 keV and a peak energy E_p<15 keV. XRF 050406 is one of the first examples of a well-studied X-ray light curve of an XRF. We show that the main afterglow characteristics are qualitatively similar to those of normal GRBs. In particular, X-ray flares superimposed on a power-law light curve have now been seen in both XRFs and GRBs. This indicates that a similar mechanism may be at work for both kinds of events.

Long afterglow phosphorescent characteristics of BaAl 2O 4:Eu,Dy films

BaAl 2O 4:Eu,Dy (BAO) films have been fabricated on Si substrate by laser ablation, and their fundamental optical property and afterglow characteristics are discussed in comparison with the SrAl 2O 4:Eu,Dy (SAO) films. The intense green emission near 500 nm that originates from 5d to 4f transition in Eu 2+ ions was clearly observed from the BAO films. This photoluminescence peak was at a shorter wavelength than that of the SAO films ( λ = 520 nm). The afterglow intensity from the BAO films disappeared within a few minutes whereas that of the SAO films lasts over 20 min. The hole-trap depth ( E t) created by Dy as the auxiliary activators, which strongly affects the afterglow characteristics, was estimated on the basis of the thermally stimulated luminescence (TSL) result. The TSL glow curve for BAO films showed two broad peaks at 320 K and 450 K. The calculated E t for each peak was 0.2 eV (for the 320 K peak) and 1.2 eV (for the 450 K peak). On the other hand, E t = 0.5 eV was obtained from the SAO films. The hole-trap depths of the BAO film are either too shallow or too deep to affect the afterglow characteristics at room temperature.

The State of the Circumstellar Medium Surrounding Gamma‐Ray Burst Sources and Its Effect on the Afterglow Appearance

We present a numerical investigation of the contribution of the presupernova ejecta of Wolf-Rayet stars to the environment surrounding gamma-ray bursts (GRBs), and describe how this external matter can affect the observable afterglow characteristics. An implicit hydrodynamic calculation for massive stellar evolution is used here to provide the inner boundary conditions for an explicit hydrodynamical code to model the circumstellar gas dynamics. The resulting properties of the circumstellar medium are then used to calculate the deceleration of a relativistic, gas-dynamic jet and the corresponding afterglow light curve produced as the shock wave propagates through the shocked-wind medium. We find that variations in the stellar wind drive instabilities that may produce radial filaments in the shocked-wind region. These comet-like tails of clumps could give rise to strong temporal variations in the early afterglow lightcurve. Afterglows may be expected to differ widely among themselves, depending on the angular anisotropy of the jet and the properties of the stellar progenitor; a wide diversity of behaviors may be the rule, rather than the exception.

Long afterglow characteristics of thin film phosphor fabricated by laser ablation

Long afterglow phosphorescent SrAl 2O 4:Eu,Dy thin films have been fabricated on Si substrate by laser ablation. The thin film phosphors show the intense green emission near 520 nm, and additional emissions near 390 nm and near 450 nm that are originating from 5d–4f transition in Eu 2 + ions doped in the thin films. The afterglow intensity at 520 nm of the thin film phosphors was detected over 20 min later, after excitation was removed. The afterglow characteristics is almost the same between in the SrAl 2O 4:Eu,Dy thin film phosphors and the SrAl 2O 4:Eu,Dy bulk phosphors. Then, the long afterglow characteristics are interpreted by the hole trapping due to the Dy 3 + ions added as the auxiliary activator doped into the SrAl 2O 4 thin films.

Long lasting phosphorescence of Sr 4Al 14O 25:Eu 2+,Dy 3+ thin films by magnetron sputtering

This paper reports the preparation process and the long lasting phosphorescence of the Sr 4Al 14O 25:Eu 2+,Dy 3+ thin films obtained by magnetron sputtering. Phosphorescence was achieved by annealing the films in reducing atmosphere. Sr 4Al 14O 25 thin film was obtained when the films were treated at 1200 °C, while SrAl 2O 4 was generated as the intermediate phase during the annealing process. Sr 4Al 14O 25:Eu 2+,Dy 3+ film generated an emission at 485 nm, and SrAl 2O 4:Eu 2+,Dy 3+ film showed an emission peaking at 515 nm. Afterglow characteristics were observed for both films, and Sr 4Al 14O 25:Eu 2+,Dy 3+ film showed a better afterglow property than the SrAl 2O 4:Eu 2+,Dy 3+ film due to a deeper trap level and a higher trap concentration formed in the thin films.

Photoluminescence of 4SrO·7Al 2O 3 ceramics sintered with the aid of B 2O 3

4SrO·7Al 2O 3 long persistent ceramics with different B 2O 3 contents prepared by sintering were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence spectrum (PLS). The ceramics showed a two peak emission at 400 and 486 nm, due to the different lattice sites Eu 2+ ions held in the 4SrO·7Al 2O 3 lattice. B 2O 3 plays several different roles in the ceramics. In the synthesis process, it greatly promotes the formation of 4SrO·7Al 2O 3 phosphor and helps to form dense ceramics at 1400 °C. Furthermore, with the addition of B 2O 3, the emission peaks shifted to the short wavelength side due to lattice contraction. The afterglow characteristics result from the emission at 486 nm other than the emission at 400 nm. The duration of the phosphor was enhanced by the addition of B 2O 3, due to the trap center formed in the 4SrO·7Al 2O 3 host.

Effects of adding B2O3 as a flux on phosphorescent properties in synthesis of SrAl2O4: (Eu2+, DY3+ phosphor

SrAl2O4: (Eu2+, Dy3+) phosphor was prepared by solid state reaction. B2O5 as a flux was added in SrAl2O4:(Eu 2+, Dy3+) in order to accelerate a solid state reaction. In this paper, the effects of B2O3 on the crystal structure and the phosphorescent properties of the material have been evaluated. The synthesized phosphor exhibited a broad band emission spectrum peaking at 520 nm, and the spectrum peak showed little effect by the B2O3 contents. The maximum afterglow intensity of the SrAl2O4: (Eu2+, Dy3+) phosphor was obtained at the B2O3 content of 5%. Adding the B2O3 caused uniform distortion to the crystal structure of the phosphor and resulted in reducing the lengths of a and c axes and Β angle of the SrAl2O4 crystal. The uniform distortion was accompanied with crystal defects which can trap the holes generated by the excitation of Eu2+ ions. The afterglow characteristic of the SrAl2O4: (Eu2+, Dy3+) phosphor was thus enhanced.

Electroluminescence of SrAl2O4:Eu2+ phosphor

The SrAl2O4:Eu2+ phosphor powders have been synthesized by sol–gel process. Electroluminescent (EL) properties of the SrAl2O4:Eu2+ phosphor were investigated using a convenient thick film device. Green light emitting at a peak of 508 nm was obtained when driven by sine alternating current (AC). The color coordinate of the emission was x=0.148 and y=0.635. Luminance–voltage and afterglow characteristics of the SrAl2O4:Eu2+ EL devices were studied. The results show that SrAl2O4:Eu2+ can be used as green phosphor for EL displays.

Preparation of Long Persistent SrO×2Al2O3 Ceramics and Their Luminescent Properties.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Preparation of long persistent SrO·2Al 2O 3 ceramics and their luminescent properties

Long lasting strontium aluminate phosphors were synthesized by solid state reaction in the experiment. SrO·2Al 2O 3 ceramics with long afterglow was firstly fabricated at 1400 °C with the aid of B 2O 3. The effects of B 2O 3 on the phase composition, porosity, density and microstructure of the sintered ceramics were investigated, as well as the effects on luminescent properties. The results indicated that B 2O 3 stimulated the formation of SrO·2Al 2O 3 by consuming the intermediate phases and helped to produce dense ceramics at 1400 °C. The ceramics hold two emission peaks at 390 and 475 nm, due to the luminescent behavior of Eu 2+ in 5SrO·4Al 2O 3 and SrO·2Al 2O 3, respectively. Emission at 390 nm showed slight afterglow characteristics while emission at 475 nm illustrated good long persistence. The afterglow property was enhanced by the addition of B 2O 3, due to the increase in the depth of the trap center in the ceramics.

Studies on the decay characteristics of strontium aluminate phosphor on thermal treatment

Strontium aluminate (SRA) based long decay phosphor has been prepared by solid-state reaction technique. The dependence of initial brightness and observed afterglow characteristics on various thermal processing parameters such as heating rates, time of constant heating and cooling rates have been investigated. It has been found that heating rates (>625°Ch−1), time of constant heating (<2h at around 1200°C) and cooling rates (>250°Ch−1) resulted in non-uniform luminescent samples which are not excited under roomlight but under UV (365nm). Whereas heating rates (<300°Ch−1), time of constant heating (>4h at 1200°C) and cooling rates (<100°Ch−1) resulted in high-density ceramic compact (∼3100kgm−3) samples with very low initial brightness but quite long afterglow under roomlight and UV excitation. An optimum of both fast rise and long afterglow under roomlight excitation has been achieved for the SRA samples fired with the heating rates of 300–625°Ch−1, time of constant heating 2–4h at around 1200°C and cooling rates of 100–250°Ch−1. The decay characteristics of SRA have been compared with established ZnS:Cu long decay phosphor.

Short Gamma‐Ray Bursts and Mergers of Compact Objects: Observational Constraints

Gamma-ray burst (GRB) data accumulated over the years have shown that the distribution of their time duration is bimodal. While there is some evidence that long bursts are associated with star-forming regions, nothing is known regarding the class of short bursts. Their very short timescales are hard to explain with the collapse of a massive star but would be naturally produced by the merger of two compact objects, such as two neutron stars (NS-NS), or a neutron star and a black hole (NS-BH). As for the case of long bursts, afterglow obervations for short bursts should help reveal their origin. By using updated population synthesis code calculations, we simulate a cosmological population of merging NS-NS and NS-BH and compute the distribution of their galactic offsets, the density distribution of their environment, and, if indeed associated with GRBs, their expected afterglow characteristics.

The afterglow characteristics of xenon pulsed plasma for mercury-free fluorescent lamps

In this study, the spectroscopic characteristics of radiations from xenon pulsed plasma are measured experimentally as a study on a mercury-free fluorescent lamp. Each radiation waveform has two peaks and they vary according to the inner diameter of lamp and the pressure of xenon as follows: (a) As the inner diameter of lamps increases, the afterglow radiation, that is the second peak, decays faster. (b) As the xenon pressure increases the first peak of radiation just after the start of discharge decreases and the afterglow increases. The characteristics of afterglow are explained by the rate equation of metastable xenon atoms Xem, and its coefficients are determined through the experimental results. This equation shows that in order to obtain intense phosphor afterglow, i.e. strong radiation of xenon excimer, high pressure of xenon and large lamp diameter are desirable. Moreover, high pressure of xenon brings fast decay of afterglow. Then the afterglow radiation has no overlap on the first peak of next discharge at a high frequency. Consequently, higher pressure of xenon and large lamp diameter are desirable for high intensity and high efficacy for xenon fluorescent lamps.

Predictions for the Very Early Afterglow and the Optical Flash

According to the internal-external shocks model for gamma-ray bursts (GRBs), the GRB is produced by internal shocks within a relativistic flow while the afterglow is produced by external shocks with the interstellar medium. We explore the early afterglow emission. For short GRBs the peak of the afterglow will be delayed, typically by few dozens of seconds after the burst. For long GRBs the early afterglow emission will overlap the GRB signal. We calculate the expected spectrum and the light curves of the early afterglow in the optical, X-ray, and gamma-ray bands. These characteristics provide a way to discriminate between late internal shocks emission (part of the GRB) and the early afterglow signal. If such a delayed emission, with the characteristics of the early afterglow, is detected, it can be used to prove the internal shock scenario as producing the GRB, as well as to measure the initial Lorentz factor of the relativistic flow. The reverse shock, at its peak, contains energy which is comparable to that of the GRB itself but has a much lower temperature than that of the forward shock so it radiates at considerably lower frequencies. The reverse shock dominates the early optical emission, and an optical flash brighter than 15th magnitude is expected together with the forward shock peak at X-rays or gamma-rays. If this optical flash is not observed, strong limitations can be put on the baryonic contents of the relativistic shell deriving the GRBs, leading to a magnetically dominated energy density.