Afterglow Time Research Articles

Dust dynamics during the plasma afterglow

The charge and dynamics of dust particles in an afterglow plasma are studied using a 1D model in the diffusion approximation, taking into account the transition from ambipolar to free diffusion. It is analyzed how external conditions (dust particle size, neutral gas pressure and initial electron density) affect the dust motion. The dust particle dynamics has been examined in microgravity conditions and in presence of gravity. Without gravity, the location of dust particles in plasma volume may change essentially during the afterglow if the dust size and pressure are small (⩽10 nm and ⩽30 mTorr, respectively). At small pressures, in the very beginning of afterglow, small nanoparticles move to the plasma boundary because the ion drag force dominates over the electric force. At afterglow times when the electron temperature becomes time-independent, the ion drag force decreases faster with time than the electric force due to the ion density decrease, and dust particles may move to the slab center. In presence of gravity, the effect of gravity force on dust particles is important only at large afterglow times (t ⩾ 10 ms), when the electric and ion drag forces are small. The dust dynamics depends essentially on the initial plasma density. If the density is large (∼1012 cm−3), small nanoparticles (⩽10 nm) may deposit on plasma walls in the beginning of plasma afterglow because of an enhancement of the ion drag force.

Green Sorbitol- and Isosorbide-Based Flame Retardants for Cotton Fabrics.

Flame retardancy is often required in various textile applications. Halogenated flame retardants (FR) are commonly used since they have good FR performance. Several of these components are listed under REACH. Halogen-free FR compounds have been developed as alternatives. So far, not many biobased FR have made it to the market and are being applied in the textile sector, leaving great opportunities since biobased products are experiencing a renaissance. In this study, renewable FR based on sorbitol and isosorbide were synthesised. The reaction was performed in the melt. The resulting biobased FR were characterised via FT-IR, thermogravimetric analysis (TGA) and X-ray fluorescence (XRF). Cotton fabrics functionalized with the developed biobased FR passed ISO 15025 FR test. After washing, the FR properties of the fabrics decreased (longer afterflame and afterglow time) but still complied with ISO 15025, indicating the biobased FR were semi-permanent. The amount of residue of modified sorbitol and isosorbide measured at 600 °C in air was 31% and 27%, respectively. Cotton treated with biobased modified FR showed no ignition during cone calorimetry experiments, indicating a flame retardancy. Furthermore, a charring of the FR containing samples was observed by means of cone calorimetry and TGA measurements.

Application of Eigenvalues and Eigenvectors in Correlating Density and Fire Properties of Some Selected Woods in South-East Nigeria

Data sourced from literature for wood density (WD) and fire properties for fifteen Nigerian woods were analysed. The fire properties are ignition time (IT), flame propagation rate (FPR), flame duration (FD), afterglow time (AGT), ash formation (AF) and limiting oxygen index (LOI). The aim was to correlate density and fire properties of wood using eigenvalues and eigenvectors. The analysis tool adopted was the statisticalanalysis system (SAS) where principal component and regression analyses were performed. Based on the presented data and analyses, WD was found to relate well with FPR, AGT and LOI with an adjusted R-Square = 83% while the other three parameters: IT, FD and AF constitute random noise.
 2.11.0.0
 2.11.0.0

Application of Eigenvalues and Eigenvectors in Correlating Density and Fire Properties of Some Selected Woods in South-East Nigeria

Data sourced from literature for wood density (WD) and fire properties for fifteen Nigerian woods were analysed. The fire properties are ignition time (IT), flame propagation rate (FPR), flame duration (FD), afterglow time (AGT), ash formation (AF) and limiting oxygen index (LOI). The aim was to correlate density and fire properties of wood using eigenvalues and eigenvectors. The analysis tool adopted was the statisticalanalysis system (SAS) where principal component and regression analyses were performed. Based on the presented data and analyses, WD was found to relate well with FPR, AGT and LOI with an adjusted R-Square = 83% while the other three parameters: IT, FD and AF constitute random noise.
 2.11.0.0
 2.11.0.0

Investigation on the luminescent properties of a novel Bi3+ based blue long afterglow phosphor Ca14Ga10Zn6O35:Bi3+

A series of Bi3+ based blue long afterglow phosphor Ca14Ga10Zn6O35:Bi3+ were successfully synthesized via solid state reaction method. Under ultraviolet excitation of the samples, a blue emission originated from 3P1→1S0 transition of Bi3+engendered a broadband from 380 to 600 nm with peak at around 432 nm. The peak positions of the emission curves have experienced a slight red shift from 432 to 442 nm when the concentrations of Bi3+ were increased from 0.1 % to 1.5 %. After excitation stopped, the persistent luminescence from Bi3+ ions could last more than half an hour. The afterglow duration times were shortened remarkably with the increasing concentration of Bi3+, from several thousand seconds to several hundred seconds, along with decreased afterglow intensity. With the alkaline metals Li+ and Na+ co-doped to provide charge compensation, the emission intensity of Bi3+ ions was increased, together with compensated by the shortened persistent time. A series of thermoluminescence glow curves of 0.1 % Bi3+ doped sample were measured with different delay times to detect the population dynamics of traps. With the systematical experimental results, a reasonable model was proposed to illuminate the mechanism of the emission and persistent phenomenon of this promising novel Bi3+ based blue long afterglow phosphor.

Li2CaSi2N4:Sm3+: A nitride-based red phosphor with excellent temperature sensitivity and cathodoluminescence for temperature sensor and FED

Temperature sensor and field emission displays (FED) are the intensive topics for Sm3+ activated red phosphor. In this study, a novel lithium nitride red phosphor Li2CaSi2N4:Sm3+ was successfully prepared by solid phase method. The photoluminescence and cathodoluminescence performances were systematically studied to explore the possibility in FED and temperature sensor applications. The results indicate that the Li2CaSi2N4:Sm3+ phosphor features intense red emission under the UV light and cathode ray excitations. The phosphor also has a long red afterglow with an afterglow time of 12.7 min. Most importantly, Li2CaSi2N4:Sm3+ exhibits excellent temperature sensitivity with the relative sensitivity of 4.8% K−1 @473 K, which is higher than other temperature sensor materials. The thermal quenching mechanism was proposed based on a configurational-coordinate model. Moreover, excellent cathode ray saturation and aging resistance were observed in Li2CaSi2N4:Sm3+. The results indicate that Li2CaSi2N4:Sm3+ is a potential temperature sensor and FED materials.

Preparation and Reliability of Wearable Blue Light-Storing Buttons

The potential applications of light-storing materials have stimulated the exploration of the preparation of wearable light-storing buttons. In this study, Sr2MgSi2O7:Eu2+, Dy3+ was mixed with unsaturated polyester resin in proportion as a light-storing material. A blue phosphorescent button with high stability and long afterglow time is obtained through the dispensing method. The surface, cross morphology, phase structure, photoluminescence spectrum, luminescence image, afterglow performance and mechanical hardness of the phosphorescent button were characterized. The results show that the luminescence performance of the phosphorescent button is significantly better than that of the original material Sr2MgSi2O7:Eu2+, Dy3+ after high temperature and high humidity aging, xenon lamp aging, and thermal cycle aging tests. In this study, the afterglow time button of the light-storing button is very beneficial. At the same time, it has also expanded the application of long afterglow materials in the field of smart wear.

Influence of co-doping germanium ions on the long persistent near-infrared luminescence of ZnAl2O4:Cr3+

A series of infrared long persistent phosphor samples of ZnAl2O4: Cr3+ with various doping concentrations of Ge4+ ions were synthesized via a high temperature solid state reaction method. Powder X-ray diffraction, persistent spectra, afterglow decay curves, photoluminescence and isometric thermoluminescence spectra were collected to identify the influence of the Ge4+ ions on the luminescence in the spinel structure. The results define an optimal co-doping of germanium ions (2 mol%) in the ZnAl2O4: Cr3+ can enhance the afterglow time of the phosphor. With the increase of co-doping, the diffraction peaks shift to the shorter angles which confirm a swelling of the crystal cell. Thermoluminescence data emphasise there are modifications from the presence of the Ge ions. The phenomenon that the long-wave emission reaches the maximum value of the spectral spread before the short-wave signal provides interesting insights into the charge transfer process.

Preparation and reliability of wearable light-storing buttons

The potential for a large number of applications has stimulated the exploration of the preparation of wearable light-storing buttons. In this study, SrAl2O4：Eu2+, Dy3+ (SROED) was used as a long-lasting phosphorescent material, mixed with unsaturated polyester resin in proportion. A light-storing button with high stability and long afterglow time is obtained by the dispensing method. The surface and cross morphology, phase structure, photoluminescence spectrum, luminescence image, afterglow performance and mechanical hardness of the luminescent button are characterized. The results show that the luminescence performance of the phosphorescent button is significantly better than that of the original luminescent material SROED after high temperature and high humidity aging, xenon lamp aging, and thermal cycling aging test. Even in this study, the afterglow life of light-storing buttons can be maintained up to 7h. The luminescence mechanism of light-storing buttons is also discussed. This result will be very beneficial for the preparation of high-quality light-storing buttons. At the same time, it also expands the application of long afterglow materials in the field of smart wearables.

Improving red afterglow properties of CaZnGe2O6: Mn2+ by co-doping Bi3+

Bi3+, Mn2+ co-doped CaZnGe2O6 red long afterglow materials were prepared by high temperature solid state reaction method. The phosphor has broad excitation band ranging from 220 nm to 350 nm with two peaks at 255 nm and 300 nm and can give blue, green and red emission band peaking at 448 nm, 530 nm and 645 nm, respectively. Due to the emission properties of Bi3+ ions and the Bi3+→Mn2+ energy transfer, the co-doped Bi3+ ions can not only enhance the PL luminescence of the phosphor, but also adjust the emission color. After irradiation of 300 nm ultraviolet light, the phosphors exhibits long-persistent red phosphorescence. Thermoluminescence tests demonstrate that the introduction of Bi3+ ions can increase the trap depth and trap concentration, greatly improving the afterglow time and brightness of the CaZnGe2O6: Mn2+ phosphor. The present work might provide reference for designing new rare earth free red long afterglow materials.

Red afterglow and luminescence arising from defects in CaS:Eu2+, Tm3+

CaS:Eu2+, Tm3+ is a phosphor known to emit a long afterglow of red emission (650 nm) when excited by blue light (450 nm). It shows a long afterglow time of 700 s for Eu = 0.05% and Tm = 2%. The mechanism of this afterglow is investigated using time-resolved fluorescence (TR-F) spectroscopy from the nanosecond to millisecond region. At room temperature, it is not possible to investigate shallow levels because of the effects of thermal vibrations. The mechanism of the emission characteristics at room temperature would be affected by these levels that can be observed only at low temperatures. Therefore, the samples are cooled to 15 K for the TR-F measurements. The host material CaS emits blue light (420 nm) arising from sulfur defects, and the typical decay time is measured to be 6 ms. This blue emission becomes stronger when Tm3+ is doped. Furthermore, the doped Eu ions emit a broad red spectrum at 650 nm originating from the Eu2+-specific 4f65d1–4f7 transition. When the excitation is ceased, the red emission decays with a fast time constant of 0.6 μs. This value is a typical decay time for Eu2+. This red emission has multiple decay time constants, and a component with a decay time of 6 ms appears. This 6 ms decay time is the same as that of the blue emission from the sulfur defects, which have an important role on the red afterglow.

Morphology control and synthesis of afterglow materials with a SrAl2O4 framework synthesized by Surfactant-Template and hydrothermal methods

Afterglow materials, which are also known as persistent emitters, have a long emission lifetime that varies from seconds to tens of minutes. These materials have shown potential applications in photoenergy conservation devices such as evacuation signage and emitting lines in a motorway surface. In this study, we synthesized afterglow materials, Eu2+, Dy3+@SrAl2O4, wherein the emitting agents (Eu2+ and Dy3+) are co-doped in a SrAl2O4 framework, which was confirmed by X-ray diffraction. The liquid-state reaction process plays a crucial role in the synthesis of materials. When the surfactant-template method is used for synthesis, reverse micelles, which control the morphology of afterglow product, hold the raw reactant materials, thereby yielding characteristic morphologies of approximately 40–80 nm. The reverse micelles have been detected by small-angle X-ray scattering in this study. In contrast, the hydrothermal method produces morphologies up to approximately 2–3 μm. Results suggest that both the synthetic routes yield similar emission spectra and mean afterglow time of ~ 10 s.

Improved luminescence and afterglow emission from Mn2+/Si4+ co-doped AlN by combustion synthesis method

An orange-red emitting Mn2+/Si4+ co-doped AlN phosphor was prepared by an efficient combustion synthesis method. Phase identification and structure characterization were performed using powder X-ray diffraction (XRD) and refined by the Rietveld method. Luminescence and afterglow properties of the AlN-based phosphors such as photoluminescence spectra (PL), CIE values, afterglow decay curves, thermoluminescence glow curves (TL) were systematically studied. Using the Tanabe-Sugano diagram, the Racah parameters B, C, and crystal field splitting parameter Dq of as-prepared phosphor were calculated to be 812 cm−1, 2168 cm−1, and 780 cm−1, respectively. The luminescence intensity and afterglow time were increased, respectively, by about 1.1 and 2.2 times after 3% Si4+ co-doping. Particular attention was paid to study the mechanism of Si4+ co-doping on improving luminescence properties using a combination of the above-mentioned method and X-ray photoelectron spectroscope (XPS). Two hypothetical stress cancellation and charge rebalance effects due to Si4+ co-doping were discussed. Besides, it was found a shallower trap level (0.56 eV, compared to 0.84 eV for those without Si4+ co-doping) was formed after the co-doping of Si4+, which results in enhanced afterglow performance.

Multifunctional room-temperature phosphorescent carbon dots for relative humidity determination and information encryption

The relative humidity (RH) determination is crucial in many fields. Based on the phosphorescent properties of room-temperature phosphorescent (RTP) carbon dots, the RTP carbon dots as a probe are expected to be used to rapidly detect relative humidity. In this study, matrix-free room-temperature phosphorescent N-doped carbon dots (N-CDs) were successfully prepared from urea, succinic acid, and acrylamide using a hydrothermal method. The as-synthesized N-CDs had good biocompatibility and water solubility. The N-CDs emitted blue fluorescence and green phosphorescence. Moreover, the N-CD powder exhibited stable phosphorescence with a phosphorescence lifetime of 158 ms (afterglow time to the naked eye for ~7 s). Because H2O molecules affected the afterglow time, the as-prepared N-CD test paper for the first time could be applied as a probe to monitor RH, the afterglow time of the N-CD test paper is linearly related to the RH (y = −0.0729x+7.042, R2 = 0.998) and the RH detection range is 0%–85%. And the results were consistent with those obtained using a hygrometer. In addition, the N-CD solution could also be used as an encryption ink in the advanced information security field.

Luminescent properties of a ZnO whisker array as a scintillation detector material

We have studied luminescent properties of a ZnO whisker array, a promising crystalline material for scintillation detectors, capable of ensuring a fast and strong response and a short afterglow time. Measurements have been performed under X-ray and UV optical excitation. We present a comparative analysis of spectral features of the near-band-edge emission of the whisker array at low (∼80 K) and room temperatures in relation to the excitation method.

Electrospun PU/MgO/Ag Nanofibers for Antibacterial Activity and Flame Retardency

Antibacterial activity and fire retardation are equally desired for protective clothing. For achieving this, AgNP and MgO are independently researched as nanofillers in Polyurethane based electrospun nanofibers and their synergistic effect is scarcely addressed. This article reports synthesis and characterization of MgO of 70.01 nm and AgNP of 51 to 76 nm by solution combustion and hydrothermal routes respectively and their incorporation in electrospinning of Polyurethane. Flow rate 1 ml/hr, applied voltage 13 kV, tip to collector distance 15 cm were adopted for the electrospinning. Nanofibers of 65 nm were obtained for PU/MgO (3 wt. %) and 106 nm for PU/MgO (3 wt. %)/Ag (1 wt. %). Addition of MgO increased the melting point, after flame time and afterglow time. Incorporation of AgNP improved antibacterial activity. PU/MgO/Ag (2 wt. %) exhibited zone of inhibition of 2.1 cm and 3 cm against E. Coli and S. Aureus, respectively.

Preparation of Zn3Ga2Ge2O10:Cr3+, Al3+ nanometer phosphors via sol-gel method

In this paper, the near-infrared luminescence Zn3Ga2Ge2O10:Cr3+, Al3+ prepared by citrate sol-gel method is studied. When the Cr3+ doping amount is 0.01% and the Al3+ doping amount is 0.2, the prepared Zn3Ga2Ge2O10: The afterglow properties of Cr3+, Al3+ afterglow nanomaterials are the best. The sample has the least heterogeneous phase, the highest crystallinity, the longest afterglow time, the excitation peak at 267 nm and the emission peak at 745 nm. The light produced belongs to the wavelength range of near-infrared light. After excitation with an ultraviolet lamp, the material can see deep cherry red light in the dark.

High Performance of Simple Organic Phosphorescence Host-Guest Materials and their Application in Time-Resolved Bioimaging.

The study of purely organic room-temperature phosphorescence (RTP) has drawn increasing attention because of its considerable theoretical research and practical application value. Currently, organic RTP materials with both high efficiency (ΦP > 20%) and a long lifetime (τP > 10 s) in air are still scarce due to the lack of related design guidance. Here, a new strategy to increase the phosphorescence performance of organic materials by integrating the RTP host and RTP guest in one doping system to form a triplet exciplex, is reported. With these materials, the high-contrast labeling of tumors in living mice and encrypted patterns in thermal printing are both successfully realized by taking advantage of both the long afterglow time (up to 25min in aqueous media) and high phosphorescence efficiency (43%).

Synergistic Effect and Flame-retardant Properties of Small Molecular Organic Amines and Phosphates

The flame-retardant finishing of cotton with pentaerythritol phosphate and small molecule organic amine, such as diethylenetriamine, triethylenetetramine, diethanolamine, or isopropanolamine, was studied. The mechanical and flame-retardant properties and thermal stability of cotton fabric before and after flame-retardant finishing were investigated. Results revealed that the longitudinal and latitudinal breaking strength increased. The limiting oxygen index increased from 18.7 % to 37.9–39.1 %. Vertical flame burning time and afterglow time decreased from 35.1 and 8.4 s, respectively, to 0 s. The damage length decreased from 30 cm to 7.1–8.4 cm. At 700 °C, the residual carbon increased from 17.69 % to 41.48–41.56 %. The experimental results show that the flame-retardant system has good flame retardant and carbonization effects on cotton and good foaming property for combustion. The experimental operation is simple, rapid, and has broad market prospects.

The influence of doped Cr ions on the luminescence properties of infrared long persistent phosphor ZnAl2O4 with the substitution of Ge ions

A series of Zn1·8Al1.6Ge0.2O4: Cr3+ x mol% (x = 0.5, 1, 1.5, 2, 2.5, 3) phosphors were synthesized via a high temperature solid state reaction. It was shown in the previous study that suitable germanium substitution in the original ZnAl2O4: Cr3+ infrared long persistent phosphors can enhance the afterglow time. In this paper, powder X-ray diffraction, afterglow decay curves, photoluminescence and isometric thermoluminescence spectra were collected to identify the influence of the Cr ions on the luminescence in the spinel structure. With the increase of doping, the diffraction peaks shift to the shorter angles which confirm a swelling of the crystal cell. Meanwhile, according to the photoluminescence, the excitation emissions of Cr3+ shift which respond to the structural changes. The Stoke and anti-Stoke lines of Cr3+ infrared emission are noticeable for these samples and the dependence of these lines with temperature is demonstrated. Both thermoluminescence (TL) and afterglow results prove that 1.5 mol% Cr is the optimized doping concentration. All the results indicate that with a suitable concentration, Zn1·8Al1.6Ge0.2O4: Cr3+ could be prepared as an excellent infrared long afterglow phosphor and the emission lines of Cr ions are excellent probe ions that record structural changes.