Afterglow Time Research Articles

Optical properties of near infrared persistent phosphor CaZnGe2O6: Cr3+, M3+ (M3+ = B3+; Al3+; Ga3+)

Persistent luminescence (PersL) is a phenomenon when a material continues to emit light for a period of time, usually several minutes or hours after the removal of the excitation source. Although it is possible to find several hundred different materials suitable for the observation of PersL in the visible part of the spectrum, only a handful of them is applied to obtain phosphors for near infrared (NIR) emission. In the course of this work, CaZnGe2O6: Cr3+, M3+ (M3+ = B3+; Al3+; Ga3+) materials have been synthesized by a melt crystallization method. Photoluminescence (PL) and subsequent PersL of chromium ions in the NIR spectral region, as well as visible PL and PersL of the host material, have been observed. After irradiation with ultraviolet (UV) radiation, a broad NIR PersL band with a maximum around 790 nm and an afterglow time over 1 h has been detected. The addition of B3+; Al3+; Ga3+ increases the overall intensity and duration of PersL. The analysis of PersL decay curves and glow curves of thermally stimulated luminescence (TSL) show multiple trap centres involved in the generation of PersL.

Influence of luminescent powder type and characteristic on the glow light performance of architectural glass mortar

The effect of luminescent powder (LP) type and characteristics on the properties of architectural luminescent glass-mortars (ALM) was investigated. Four LPs including ZnS:Cu (LP1) and SrAl2O4:Eu2+,Dy2+ (LP2-4) with different particle sizes and surface conditions (with or without a protective layer) were coated on the surface of glass particles using an adhesive paint for producing luminescent glass (LG). LG was then used to replace coarse aggregate in conventional glass mortar for the production of ALM. The results showed that all ALMs obtained good fresh properties and mechanical strength (>40 MPa) with proper excitation and emission wavelengths ranging from 250 to 450 nm and 500–560 nm, respectively, demonstrating the feasibility of fabricating decorative concrete. Regarding the glow light performance, SrAl2O4:Eu2+,Dy2+ outweighed ZnS:Cu in all luminescent indexes including initial brightness (luminescent intensity), decay rate, and afterglow time. Coarser LP attained lower luminescent intensity but a better decay rate due to the its relative lower specific surface area. A protective layer on the LP surface (surface condition) inhibited its light absorption and emission capacity, leading to poor luminescent performance. The adhesive paint used for producing LG, having poor UV aging resistance, was susceptible to sunlight degradation, reflected by colour turning into brown. The darker colour reduced its light transmitting efficiency, inducing a decrease in glow light performance of ALM. The excellent water and wearing resistance of ALM allowed maintaining their luminescent performance under extreme environment conditions.

Comparative Study of Influence of Experimental Configuration on Densities of Active Species in the Early Afterglows of N2/(0–2.5%)H2 HF Flowing Plasmas

Afterglows of mixed gas of N2 and H2(0–2.5%) flowing microwave discharges in a 5 mm diameter tube connected to a 5 L reactor via a tube of 1.8 cm diameter and 50 cm long, have been studied using optical emission spectroscopy. The obtained results at the entrance of the afterglow tube of 1.8 cm diameter: Short time afterglow (SA), (10–3 s) and inside the 5 L reactor: Long time afterglow (LA), (10–2 s) were then compared. It was found that, in N2 at 2 Torr, 0.5 slpm, the active specie density ratios had a constant value of 10–2 for N/N2, but decreased respectively from 10–3 to 10–4 for N2 (X,v > 13)/N2 and from 10–6 to 10–8 for N+2 /N2. By directly connecting the discharge tube inside the 5 L reactor, the density increases by 10 for N2 (X,v > 13) and by 102 for N2+ by changing the afterglow from LA(10−2 s) to a SA(10–3 s). Moreover and by adding 1% of H2 to N2, the N/N2 and H/H2 ratios had constant values of 1% and 0.2% respectively. The SA(10–3 s) appeared to be more efficient for surface treatments than the LA (10–2 s).

Production of intense pulsed beams of highly charged ions from a superconducting electron cyclotron resonance ion source

An experimental study of the afterglow mode was performed with a third generation electron cyclotron resonance ion source, SECRAL-II (Superconducting ECR ion source with Advanced design in Lanzhou No. II), under double frequency heating. The experimental results show that intense pulsed beams of highly charged ions (e.g., $266\text{ }\text{ }\mathrm{e}\ensuremath{\mu}\mathrm{A}$ of ${^{129}\mathrm{Xe}}^{34+}$ and $169\text{ }\text{ }\mathrm{e}\ensuremath{\mu}\mathrm{A}$ of ${^{129}\mathrm{Xe}}^{38+}$) could be produced at high frequency ($24+18\text{ }\text{ }\mathrm{GHz}$) and high power ($\ensuremath{\sim}8\text{ }\text{ }\mathrm{kW}$), even compared with the beam intensity records of SECRAL-II obtained in continuous wave (cw) mode at higher microwave frequency ($28+18\text{ }\text{ }\mathrm{GHz}$) and higher power ($\ensuremath{\sim}10\text{ }\text{ }\mathrm{kW}$), the gain factor is also up to $\ensuremath{\sim}3$. Meanwhile, it is found that the afterglow decay time in our study is much longer than that obtained with the second generation ECR ion sources typically operating at 10--18 GHz, and the corresponding peak duration is greater than 2 ms. This study provides a viable solution for heavy ion synchrotron accelerator complex such as High Intensity Heavy Ion Accelerator Facility project that requires intense pulsed beams of highly charged ions with long peak duration.

Preparation and optical properties of CaYAl3O7:Eu2+, Dy3+ phosphors with blue long afterglow luminescence

In this paper, a new blue long afterglow luminescent material CaYAl3O7:Eu2+, Dy3+ was prepared by high-temperature solid-phase method. The physical phase analysis was carried out by X-ray diffraction; the elemental valence analysis was conducted by X-ray photoelectron spectroscopy; the luminescence properties of the samples were characterized by fluorescence spectrometer and UV absorption spectrometer; and the afterglow properties were measured by afterglow spectrometer. The results show that the doping of Eu2+ and Dy3+ did not change the physical phase of the crystals. In this long afterglow material, the introduction of Dy3+ as a trap center did not change the shape of the excitation and emission spectra of the samples, but the afterglow brightness can be significantly enhanced. The best afterglow performance was achieved when the doping concentration of Dy3+was 1%, with an afterglow time of 109 min for a brightness greater than 3.2 mcd/m2 discernible to the naked eye.

A Benzene Ring‐Linked Dimethylamino and Borate Ester‐Based Molecule and Organic Crystal: Efficient Dual Room‐Temperature Phosphorescence with Responsive Property

AbstractPure organic crystal of N,N‐di‐methyl‐4‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)aniline (DMAB) exhibits efficient room‐temperature phosphorescence (RTP) with an emission maximum at 387 nm and a high phosphorescence efficiency of 35.2%. Significantly, DMAB shows an exceptional photo‐induced ultra‐long RTP (URTP) at 539 nm, which displays an afterglow time of 14 s in air. The two phosphorescent bands are attributed to the monomeric and aggregated RTP of DMAB, respectively. Continuous UV irradiation for ≈1 min can dramatically improve the lifetimes for both of the monomeric and aggregated phosphorescent emissions. The photo‐induced URTP can be spontaneously switched off after standing the crystal in air for 50 min, and this cyclic process has been repeated several times. The molecular packing based on multiple intermolecular noncovalent interactions is adopted in DMAB crystal, which is beneficial to RTP. Upon UV irradiation, the consumption of oxygen in the crystal matrix accounts for the distinctive photo‐induced URTP. Taking advantage of the unique photo/oxygen‐sensitive properties, DMAB crystals have been successfully utilized in oxygen sensing and anticounterfeiting.

Eco-friendly flame-retardant Xuan paper via layer-by-layer assembly organic/inorganic composite coating on pulp fiber

Positively charged chitosan (CS) and negatively charged montmorillonite (MMT) were layer-by-layer (LBL) assembled on Xuan paper pulp fiber to fabricate an organic/inorganic flame-retardant coating. The Xuan paper achieved a limiting oxygen index (LOI) value of 24.6% when the pulp fiber was treated by 20 bilayers (BLs) of CS/MMT coating, and its vertical flame properties also improved with less after-flame and after-glow times compared to the untreated one. These results demonstrated that the flame retardancy of Xuan paper could be enhanced by this organic/inorganic composite coating. Thermogravimetric (TG) analysis results revealed that LBL assembly of CS/MMT coating on pulp fiber improved the thermal stability at higher temperature and promoted char formation, showing the obvious condensed phase flame retardant action. Scanning electron microscopy results further confirmed that the treated Xuan paper by CS/MMT coating on pulp fiber promoted the char formation and formed the stable covering layer. The ink wetting property of Xuan paper was not influenced through the LBL assembly flame-retardant treatment of the pulp fibers by CS and MMT. This research provides a new approach for flame-retardant Xuan paper without influencing its ink wetting property using the eco-friendly organic/inorganic composite flame-retardant system.

Assembled hybrid films based on sepiolite, phytic acid, polyaspartic acid and Fe3+ for flame-retardant cotton fabric

Abstract To impart durable flame retardant property to cotton fabric, a kind of multilayered hybrid film based on environmentally friendly phytic acid, sepiolite, polyaspartic acid, and Fe3+ were deposited on the surface of cotton fabric by layer-by-layer and spraying method to form a dense protective layer. Compared with cotton fabric, hybrid film coated cotton showed excellent flame retardant property and low fire hazard, which can be demonstrated by vertical flame test, limiting oxygen index (LOI) and cone calorimeter test. After-flame time and after-glow time of hybrid film coated cotton is 1 s and 1 s, respectively. LOI value of hybrid film coated cotton increased by 44.4% compared with control sample. Cone calorimeter test revealed a total heat release rate reduction of 52.6% and peak heat release rate reduction of 73.6% for hybrid film coated cotton fabric. This work demonstrates that the hybrid film composed of phytic acid, sepiolite, polyaspartic acid, and Fe3+ could improve the durable flame retardant property of cotton fabric.

Biocompatible Probes Based on Rare-Earth Doped Strontium Aluminates with Long-Lasting Phosphorescent Properties for In Vitro Optical IMAGING.

In recent decades, the demand for biomedical imaging tools has grown very rapidly as a key feature for biomedical research and diagnostic applications. Particularly, fluorescence imaging has gained increased attention as a non-invasive, inexpensive technique that allows real-time imaging. However, tissue auto-fluorescence under external illumination, together with a weak tissue penetration of low wavelength excitation light, largely restricts the application of the technique. Accordingly, new types of fluorescent labels are currently being investigated and, in this search, phosphorescent nanoparticles promise great potential, as they combine the interesting size-dependent properties of nanoscale materials with a long-lasting phosphorescence-type emission that allows optical imaging well after excitation (so avoiding autofluorescence). In this work, core-shell structures consisting of SrAlO:Eu,Dy luminescent cores encapsulated within a biocompatible silica shell were prepared, showing a green persistent phosphorescence with an afterglow time of more than 1000 s. A high-energy ball milling procedure was used to reduce the size of the starting phosphors to a size suitable for cellular uptake, while the silica coating was produced by a reverse micelle methodology that eventually allows the excitation and emission light to pass efficiently through the shell. Confocal fluorescence microscopy using HeLa cancer cells confirmed the potential of the all-ceramic composites produced as feasible labels for in vitro optical imaging.

One-step construction of bifunctional nanoprobes for NIR afterglow and T2-weighted MR imaging

In this study, spinel-phase Zn2Ga3-xFe3+xGe0.75O8 (x = 0, 0.002, 0.004, 0.02, 0.04, 0.08, 0.2) and Zn2Ga2.98-xFe3+xCr0.02Ge0.75O8 (x = 0, 0.0004, 0.001, 0.002 0.003, 0.004) nanoparticles were prepared by one-step hydrothermal method in combination with vacuum annealing. For ZGGO: Fe3+ nanoparticles, the near infrared (NIR) emissions (∼725 nm) originate from the 4T1(4G)→6A1(6S) transition of Fe3+ occupying octahedral and tetrahedral sites of Ga3+. Furthermore, their afterglow time is more than 15 min and Fe3+ doping will influence the generation of antisite defects pair (GaZn0−ZnGa′). For Cr3+ and Fe3+ co-doped ZGGO nanoparticles with average size of ∼46 nm, the NIR persistent luminescence around ∼700 nm, originating from the 2E→4A2 and 4T2→4A2 transitions of Cr3+, can be observed and the afterglow time exceeds 850 min. With the increase of Fe3+ concentration, the afterglow intensity decreases due to the decreased number of (GaZn0−ZnGa′) defects and deeper traps. In particular, autofluorescence-free imaging and MR imaging were successfully realized by using ZGGO: Cr3+, Fe3+0.002 nanoparticles dispersed in the simulated biological fluid environments (H2O, SLS and HSA). Their clear afterglow images can be acquired within 3 min after the stoppage of the UV irradiation and their transversal relaxivity (r2) is in the range of 227–140 mM−1s−1, which is close to the conventional Feridex T2 agent (108 mM−1s−1). Our results suggest that ZGGO: Cr3+, Fe3+ nanoprobes have potential applications in the diagnosis and therapy of disease.

Synergistic flame retardant weft-knitted alginate/viscose fabrics with MXene coating for multifunctional wearable heaters

Flexible wearable heaters have received increasing attention in energy-saving, diverse personal thermal requirements, and healthcare management. Herein, considering the fire safety application of wearable heaters, the biodegradable alginate fibers and flame retardant (FR) viscose fibers are attempted to mix and weft-knit into the fabric, which interestingly exhibits synergetic flame retardancy with low afterflame time, afterglow time, and peak heat release rate. Further, assisted by the highly conductive Ti3C2Tx (MXene) nanosheets on the surface of the fabric and the periodic nested loops of the knitted fabric, the integrated fabrics possess excellent electrical performance (2Ω sq−1) with the MXene content of 9.13 wt%, electromagnetic interference (EMI) shielding efficiency of 55 dB in the X band, preferable Joule heating performance under safe low voltage (123 °C at 3.5 V) and sunlight/far-infrared heating performance. The superior flame retardancy and multifunctional properties arose from the high-temperature induced well-constructed char layer, unique functionality of interconnected MXene network and multiple scattering of light or wave. Combined with the superior flame retardancy and multifunctional properties, the weft-knitted alginate/FR viscose fabrics with MXene coating become the ideal candidate materials in the fields of wearable heaters with high safety.

Facile flame-retardant finishing for cotton in supercritical CO2

Traditional water-based flame-retardant finishing causes serious pollution due to the use of a large number of chemicals, and color change is easily generated since the flame-retardant finishing takes place after the cotton dyeing. An eco-friendly flame-retardant finishing of dyed cotton was explored using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), 2,2′-oxybis-(5,5-dimethyl-1,3,2,-dioxaphosphorinane-2,2′-disulfide) (5060), SiO2, DOPO/SiO2 (1:1), 5060/SiO2 (1:1) and DOPO/5060 (1:1) in supercritical CO2. The effects of finishing time and pressure as well as temperature on the flame-retarding properties of the cotton were discussed. As expected, samples with the higher weight gain rates exhibit a lower after-flame time as well as after-glow time. In different flame-retardant systems, cotton fabric finished with DOPO presents the lowest after-flame time of 20.6 s and after-glow time of 0 s at 130°C, 22 MPa and 120 min due to its biphenyl ring and O=P-O bond. Moreover, tiny fluctuations of L*, a*, b* and K/ S values occurred from 32.10 to 34.24, 5.78 to 6.05, –37.89 to –37.64 and 10.59 to 10.81 when the cotton samples were treated with DOPO, 5060, SiO2, DOPO/SiO2 (1:1), 5060/SiO2 (1:1) and DOPO/5060 (1:1), proving that no significant negative role in the color property of the samples occurs after supercritical CO2 finishing.

Improvement of Luminescence Characteristics of ZnGa2O4:Tb3+ Nanophosphors by Ce3+ Codoping

AbstractA series of ZnGa2O4:Tb3+,Ce3+ persistent luminescence nanophosphors were prepared by high temperature solid‐state reaction. The X‐ray diffraction (XRD) patterns of the representative samples are consistent with that of the ZnGa2O4 standard card. Scanning electron microscope (SEM) images show that the particle size of phosphor is enlarged when the Tb3+ ion is doped, however, it becomes smaller again after the Ce3+ ion is codoped. For ZnGa2O4:Tb3+ nanophosphors, there exist intense 492 and 551 nm blue/green emissions under 280 nm excitation, and the optimum Tb3+ doping concentration is 1.7 mol% and the long afterglow time is about 140 min. The PL and long afterglow characteristics of ZnGa2O4:1.7Tb3+ nanophosphor are significantly improved once the Ce3+ ion is codoped. The PL intensity of ZnGa2O4:1.7Tb3+ nanophosphor is enhanced by 1.5 times and the long afterglow time is extended to 210 min when Ce3+ doping concentrations are 0.3 and 0.5 mol%, respectively. The internal mechanism of the long afterglow effect of ZnGa2O4:1.7Tb3+,0.5Ce3+ nanophosphor is discussed in detail with the help of measurement results of thermoluminescence spectra.

Confining Carboxylized Carbon Nanotube for Phosphorescence Afterglow with Optical Memory Plasticity

AbstractAfterglow materials are of primary interest in optoelectronics and bioelectronics. Here, a long‐lived phosphorescence afterglow is reported from carboxylated carbon nanotubes (c‐CNTs) confined within boron oxynitride (BNO). The formation of covalent and hydrogen bonds in c‐CNT@BNO enhances the rigidity of the hybrid structure and alleviates the non‐radiative deactivation of excited triplet states, leading to room‐temperature phosphorescence (RTP). The afterglow material exhibits an ultra‐long RTP lifetime of up to 476.6 ms, with an afterglow time of 4.0 s, distinguishable by naked eyes. This unprecedented feature makes c‐CNT act like a light‐sensitive neuron and it is possible to achieve memorizing−forgetting behavior in the form of optical memory plasticity, owing to photons’ capture‐and‐slow‐release process. In analogy to the biological brain, both memory strength and forgetting time are proportional to learning exercise, including the intensity and time of irradiation training. The study provides an effective protocol for the synthesis of afterglow nanomaterials, extending their application to brain‐like intelligent technology.

Development of Ca2+, Cr3+ Co‐Doped and Pr3+, Ca2+, Cr3+ Tri‐Doped β‐Ga2O3 Persistent Luminescence Nanoparticles with Enhanced Luminescence

AbstractThe introduction of co‐dopants is one of the effective ways to improve the luminescence properties of the persistent luminescence nanoparticles (PLNPs). Herein, Cr3+, Ca2+ co‐doped and Cr3+, Ca2+, Pr3+ tri‐doped β‐Ga2O3 PLNPs with enhanced persistent luminescence were developed via the hydrothermal synthesis and subsequent calcinations, which improved the persistent luminescence of the β‐Ga2O3 PLNPs. The results showed that the prepared PLNPs had a long afterglow time of more than 8 days with a signal‐to‐noise ratio (SNR) of 272 and the Quantum yield (QY) up to 74.8 %, which was renewable by LED lamps and stored information under a high‐temperature environment. The synthesized β‐Ga2O3:Cr3+, Ca2+, Pr3+ PLNPs with long afterglow time showed great potentials in optical storage.

Influence of Glow and Afterglow Times on the Discharge Current of Argon at Low Pressure

An experimental investigation of the variation of argon discharge current with a glow and afterglow time intervals of a square discharge voltage was carried out at low pressure (6-11 mbar). The discharge was created between two circular metal electrodes of diameter (7.5 cm), separated horizontally by a distance (10 cm) at the two ends of a Pyrex cylindrical tube. A composite of two Gaussian functions has been suggested to fit and explain the variation graphs clearly. It is shown that the necessary times of glow and afterglow needed to attain a maximum discharge current are (70 us) and (60 us), respectively. The discharge current is observed to drop to the lowest value when the two times are serially longer than (85 us) and (72 us). Furthermore, the difference between the two times required to obtain a maximum rate of change in the discharge current, or a maximum discharge current, is deduced to be comparable to the breakdown time delay of gases reported in the literature. These observations can be useful for the design of plasma devices requiring specialized engineering.

A pyrimidine-derived diphosphine P-monoxide and a Ag(I) coordination polymer thereof: synthesis, structure, and luminescence

(4-(Diphenylphosphino)pyrimidin-2-yl)diphenylphosphine oxide is unexpectedly formed in 24% yield in the reaction of 2,4-dichloropyrimidine with 2 equiv. of Ph2PLi in THF solution. It was demonstrated that title compound reacts with AgNO3 forming 1D polymer [Ag(L)NO3], wherein P,N,O-bringing coordination of the ligand is observed. At 300 K, both free ligand and the 1D polymer exhibit solid-state photoluminescence maximized at 480 and 538 nm with 3.2 ns and 2.95 µs afterglow times, respectively.

Development of afterglow time test system for nanosecond fluorescent screen of low-level-light image intensifier

荧光屏时间特性是评价像增强器性能的重要参数之一。微光像增强器纳秒级荧光屏余辉时间目前尚缺乏测试手段，基于传统像增强器余辉时间的测试方案，研制了纳秒级荧光屏余辉时间测试系统。该系统通过采样速率250 MHz的高速信号发生器完成对激光二极管光脉冲的激励，经由下降时间为0.57 ns的光电倍增管完成对荧光屏光信号的光电转换，µA量级的微弱光电流信号经放大及单端转差分电路，在AD9684中完成AD转换，随后荧光屏数字亮度信息经现场可编程门阵列（field programmable gate array, FPGA）后存储至DDR（double data rate）单元内，经上位机发出指令实现DDR内存的读取，通过USB3.0高速传输协议至上位机中。在数据处理中采用卡尔曼滤波及快速寻找下降沿算法，实现对采集数据的噪声滤波和余辉时间的准确测量。测试结果表明，该纳秒级荧光屏余辉时间测试系统可对具有超快光学特性的像增强器进行有效测试，P47型荧光粉的余辉测试结果达到118. 094 4 ns，重复度为2.08%。

Long‐Lived Room‐Temperature Phosphorescence Based on Hydrogen Bonding Self‐Assembling Supramolecular Film

Comprehensive SummaryOrganic room‐temperature phosphorescence (ORTP) materials have attracted widespread attention in the fields of OLED, optical imaging and sensors. Herein, we successfully prepared a long afterglow IPA‐MA crystalline films using iso‐phthalic acid (IPA) and melamine (MA) by a simple drop‐casting layer‐by‐layer (LBL) method, which achieved an ultra‐long emission lifetime of up to 1.15 s. The drop‐casting LBL method is effective for the fabrication of hydrogen bonded supramolecular crystalline film materials on solid surfaces. The structure of the IPA‐MA crystalline film materials is consistent with that grown by hydrothermal method. Importantly, this method eliminates the high temperature and high pressure conditions of conventional hydrothermal methods and could form supramolecular crystalline thin films very well. In addition, the films have great long afterglow performance and the afterglow time can be controlled by altering the number of film layers. Furthermore, this method is successfully applied in the fields of temperature sensors and anti‐counterfeiting. These results not only provide the foundation for the design of organic long afterglow films, but also expand the application fields of ORTP materials.

Translucent red-emitting AlN: Mn phosphor ceramics with high luminescence thermal stability

Developing new phosphor ceramics with higher thermal conductivity is a matter of priority for high power solid-state lighting. Herein, translucent red-emitting AlN: Mn phosphor ceramic with high thermal conductivity (72.37 W m−1 K−1 at 25 °C) and high luminescence thermal stability are successfully fabricated by pressureless sintering at 1800 °C for 3 h. Preparation process, photoluminescence, afterglow and electronic compensation mechanisms were discussed in detail. TEM analysis showed that the tiny grain boundaries are composed of disordered Al2O3 phases. The EPR and TL spectra were used to reveal the O-related trap distribution. The AlN: Mn phosphor ceramics have brightly red afterglow with the longest afterglow time of 88 s and possess high luminescence thermal stability, that is to say, the luminescence intensity at 250 °C preserves 93.7% of that at room temperature. The encapsulated AlN: Mn LED device has a very bright red emission peak at 598 nm with a color purity of about 99%, indicating great application potential in solid-state lighting.