Strong Afterglow Research Articles

Sub‐10 nm Lanthanide‐Doped Lu6O5F8 Nanoscintillators for Real‐Time High‐Resolution Dynamic 3D X‐Ray Imaging

AbstractLanthanide‐doped fluoride nanoscintillators (NSs) have emerged as promising candidates for X‐ray imaging. However, strong afterglow, long lifetime, and poor irradiation stability pose key challenges for real‐time dynamic X‐ray imaging. In this study, the sub‐10 nm Lu6O5F8:Tb NSs with tunable morphologies are prepared via incorporating Li+/Na+ ions. The X‐ray excited optical luminescence (XEOL) intensity of the Lu6O5F8:15Tb/10Li NSs is stronger than that of NaLuF4:15 Tb NSs with a similar particle size while its afterglow is only ≈2.7% compared to that of NaLuF4:15 Tb NSs. Utilizing the Lu6O5F8:15 Tb/10Li NSs‐integrated film as a scintillator screen, a high resolution of ≈21.6 lp/mm is achieved. Even at a low dose of 0.23 µGy, the fringe detail in the electron device is clearly observed in the X‐ray image. The afterglow intensity of the Lu6O5F8:10Eu/10Li NSs decays to 0.7% at 40 µs, which is better than that of CsI:Tl (3.6%@40 µs). Moreover, the Lu6O5F8:10Eu/10Li NSs with a lifetime of 1.65 µs are verified for use in dynamic 3D X‐ray imaging. These findings represent a significant advancement in the development of new NSs for high‐performance dynamic X‐ray imaging.

From scintillator to phosphor: X-ray induced long afterglow red luminescence from Bi4Ge3O12:Eu3+

We have designed a novel strategy to develop efficient X-ray-induced long afterglow luminescent materials. Eu3+ ions as electron receptors were chosen as trap creators and emitting centers and scintillator Bi4Ge3O12 was regarded as the host to efficiently absorb X-ray. The obtained results showed that Bi4Ge3O12: Eu3+ can produce excellent x-ray induced red long afterglow luminescence which appeared at 589, 612, 655 and 705 nm corresponding to the 5D0→7Fj(j = 1,2,3,4) transitions, respectively. The best afterglow performance was shown when the Eu3+ doping concentration was 0.5% at this time, and Bi4Ge3O12:Eu3+ also showed a strong afterglow under short-time X-ray excitation. The thermoluminescence results indicated the X-ray irradiation can produce massive secondary electrons and the abundant free electrons can easily induce Eu3+ ions to formed Eu2+* traps, which resulted in the excellent x-ray induced long afterglow luminescence of Bi4Ge3O12: Eu3+. Furthermore, the X-ray induced long afterglow red luminescence from Bi4Ge3O12:Eu3+ can persist for more than 5400 s, which still can be clearly observed by naked eyes even after 5400 s. All these results our designed strategy can realize the development of good X-ray induced long afterglow luminescent materials from scintillator to phosphor.

Red-shift and improved afterglow of Sr3Al2-xBxO5Cl2:Eu2+, Dy3+ phosphors via a cation substitution strategy

Sr 3 Al 2-x B x O 5 Cl 2 :Eu 2+ , Dy 3+ (x = 0, 0.2, 0.4) long persistent phosphors were prepared via solid-state process. The pristine Sr 3 Al 2 O 5 Cl 2 :Eu 2+ , Dy 3+ phosphor exhibits orange/red broad band emission around 609 nm, which can be attributed to the electric radiation transitions 4f 6 5 d 1 →4f 7 of Eu 2+ . Upon the same excitation, the B 3+ -doped Sr 3 Al 2-x B x O 5 Cl 2 :Eu 2+ , Dy 3+ phosphors display red-shift from 609 nm to 625 nm with increasing B 3+ concentrations. The XRD patterns show that Al 3+ can be replaced by B 3+ in the host lattice at the tetrahedral site, which causes lattice contraction and crystal field enhancement, and thereafter achieves the red-shift on the emission spectrum. The XPS investigation provides direct evidence of the dominant 2-valent europium in the phosphor, which can be ascribed for the broad band emission of the prepared phosphors. The afterglow of all phosphors show standard double exponential decay behavior, and the afterglow of Sr 3 Al 2 O 5 Cl 2 :Eu 2+ , Dy 3+ is rather weak, while the sample co-doped with B 3+ shows longer and stronger afterglow, as confirmed after the curve simulation. The analysis of thermally stimulated luminescence showed that, when B 3+ is introduced, a much deeper trap is created, and the density of the electron trap is also significantly increased. As a result, B 3+ ions caused redshift and enhanced afterglow for the Sr 3 Al 2-x B x O 5 Cl 2 :Eu 2+ , Dy 3+ phosphor.

A novel afterglow nanoreporter for monitoring cancer therapy.

Rationale: Immunogenic cell death (ICD)-associated immunogenicity evoked through reactive oxygen species (ROS) is an efficient way to fight against the immune-dysfunctional microenvironment, so as to provoke potent anti-tumor immunity. However, the unknown ROS dose during cancer therapies may induce adverse immune responses (e.g., insufficient ICD, toxicity toward normal tissues or immune system).Methods: Herein, we developed a pyrido pyrazine - thiophene based semiconducting polymer as novel near-infrared (NIR) organic afterglow nanoparticles for the real-time visualization of self-generated ROS, during photodynamic-mediated immunogenic cell death. Specifically, we introduced the strong “acceptor” (pyrido pyrazine) into thiophene based semiconducting polymer to redshift emission wavelength, and further modulate the “donor” to afford more afterglow reaction sites and reducing ΔEst, so as to enhance luminescence intensity.Results: The semiconducting polymer-based afterglow nanoparticles exhibit strong afterglow emission with longer-wavelength emission (> 800 nm), compared with the reported organic afterglow nanoparticles (e.g., MEHPPV, PFODBT or Chlorin, < 690 nm), which endows this afterglow nanoparticles with a greatly improvement of signal to noise ratio. Moreover, the photodynamic effect of this afterglow nanoparticles can induce immunogenic cell death of cancer cells and further cause immune responses in mice.Conclusions: The NIR afterglow signal presents a good relationship with ROS generation, immunogenic cell death and outcome of treatment. Therefore, it was able to provide a non-invasive tool for predicting the degree of ICD that occurs during ROS-mediated cancer therapy and may contribute to precise immunotherapy.

Dual role of oxygen-related defects in the luminescence kinetics of AlN:Mn2.

This study presents the impact of temperature and pressure on AlN:Mn2+ luminescence kinetics. Unusual behavior of Mn2+ optical properties during UV excitation is observed, where a strong afterglow luminescence of Mn2+ occurs even at low temperatures. When the temperature increases, the contribution of the afterglow luminescence is further enhanced, causing a significant increase in the luminescence intensity. The observed phenomena may be explained by an energy diagram in which the ON-VAl complex in AlN:Mn2+ plays a key role. Hence the ON-VAl complex defect in AlN:Mn2+ plays a double role. When the ON-VAl defect is located close to Mn2+ ions, it is responsible for transferring excitation energy directly to Mn2+ ions. However, when the ON-VAl defect complex is located far from Mn2+ ions, its excited state level acts as an electron trap responsible for afterglow luminescence. Additionally, three models have been tested to explain the structure of the emission spectrum and the strong asymmetry between the excitation and emission spectra. From the most straightforward configuration coordinate diagram through the configuration coordinate diagram model assuming different elastic constants in the excited and ground-states ending by a model based on the Jahn-Teller effect. We proved that only the Jahn-Teller effect in the excited 4T1 electronic state with spin-orbit coupling could fully explain the observed phenomena. Finally, high-pressure spectroscopic results complemented by the calculations of Racah parameters and the Tanabe-Sugano diagram are presented.

Afterglow Implant for Arterial Embolization and Intraoperative Imaging.

Transcatheter arterial embolization (TAE) is wildly used in clinical treatments. However, the online monitoring of the thrombosis formation is limited due to the challenges of the direct visualization of embolic agents and the real-time monitoring of dynamic blood flow. Thus, we developed a photochemical afterglow implant with strong afterglow intensity and a long lifetime for embolization and imaging. The liquid pre-implant injected into the abdominal aorta of mice was rapidly transformed into a hydrogel in situ to embolize the blood vessel. The vascular embolism position can be observed by the enhanced afterglow of the fixed implant, and the long lifetime of afterglow can also be used to monitor the effect of embolization. This provides an excellent candidate in bio-imaging to avoid the autofluorescence interference from continuous light excitation. The study suggests the potential usefulness of the implant as an embolic agent in TAE and artery imaging during a surgical procedure.

Addressing the symmetry of a converging cylindrical shock wave in water close to implosion

We report experimental and numerical results relevant to the dynamics in the vicinity of the implosion axis of a strong shock wave generated by an underwater electrical explosion of a cylindrical array. Experiments were conducted using both sub-microsecond and microsecond timescale pulsed generators with stored energy up to ∼5 kJ, delivering ∼420/350 kA with a 320/1000 ns rise time pulses to the array, respectively. The backlighted images of the converging shock wave and the light emission around the cylindrical axis indicate strongly that the shock wave front keeps its azimuthal uniformity as far as r ≈30 μm. Also, images obtained almost simultaneously with the implosion suggest symmetric convergence &amp;lt;2 ns prior to the shockwave's arrival to the axis. In addition, the light emission obtained by a photo-multiplying tube suggests the existence of a ∼200 ns long, almost constant, strong afterglow immediately following the light emission peak related to the implosion.

Time-resolved characterization of a free plasma jet formed off the surface of a piezoelectric crystal

When a piezoelectric transformer (PT) is actuated by a low input voltage (∼10 V), electromechanical coupling leads to a very high (∼103 V) surface potential at the distal end that can ionize the surrounding gas and lead to a plasma jet emanating from the surface. PTs are attractive for non-equilibrium plasma generation because of their simple operation, low required input voltage, and low power consumption. In this work, the time-resolved characteristics of the free surface plasma jet generated by a PT operating in open air have been investigated. The temporal evolution of the PT-driven plasma was visualized by using an intensified CCD camera and plasma formation was correlated with the current behavior of the plasma jet. Notably, the plasma formation is a discrete process, appearing at a relatively fixed phase of the sinusoidal input, and the strongest plasma jet appears at the end of the positive half-cycle. Simultaneous measurements of the current show that the discharge current response is consistent with the chaotic mode for a plasma jet and appears statistically about a 1 μs earlier than plasma jet light emission, which indicates that there is a strong afterglow. With a low input voltage required for operation, these types of PT-driven plasma jets could have wide utility in emerging plasma applications beyond the laboratory, such as in healthcare and water treatment.

Luminescence and scintillation properties of strontium hafnate and strontium zirconate single crystals

The transparent single crystals of high-melting strontium hafnate (SHO) and strontium zirconate (SZO) have been grown by the floating zone method with vertical mirror arrangement. The X-ray diffraction analysis revealed orthorhombic perovskite structures for both compounds. Evaporation of Sr-containing species during the growth was proved by micro x-ray fluorescence analysis and led to slightly Sr-poor composition in the studied materials. The overall scintillation efficiency of SHO was found to be comparable with that of Bi4Ge3O12 standard scintillator, while that of SZO was considerably lower. The emission spectrum of both compounds was red-shifted when compared to the previously intensively studied powder counterparts and the photoluminescence decay curves became accelerated with pronounced nonexponentiality. The phenomenological model applied to the temperature dependences of the luminescence data revealed that in single crystals the leading luminescence process is either strongly modified with respect to powders or is of a different origin. The scintillation light yield of both materials was determined to be only several tens of photons per MeV under alpha-ray excitation due to strong afterglow, most probably related to ionization of excited state of the luminescence center.

(Invited) Red-Emitting Manganese-Doped Aluminum Nitride Phosphor

We report high efficiency luminescence with a manganese-doped aluminum nitride red-emitting phosphor under 254 nm excitation, as well as its excellent lumen maintenance in fluorescent lamp conditions, making it a candidate replacement for the widely deployed europium-doped yttria red phosphor. Solid-state reaction of aluminum nitride powders with manganese metal at 1900 °C, 10 atm N2 in a reducing environment results in nitrogen deficiency, as revealed by diffuse reflectance spectra. When these powders are subsequently annealed in flowing nitrogen at 1650 °C, higher nitrogen content is recovered, resulting in white powders. Silicon was added to samples as an oxygen getter to improve emission efficiency. NEXAFS spectra and DFT calculations indicate that the Mn dopant is divalent. From DFT calculations, the UV absorption band is proposed to be due to an aluminum vacancy coupled with oxygen impurity dopants, and Mn2+ is assumed to be closely associated with this site. In contrast with some previous reports, we find that the highest quantum efficiency with 254 nm excitation (Q.E. = 0.86±0.14) is obtained in aluminum nitride with a low manganese doping level of 0.06 mol%. The principal Mn2+ decay of 1.25 ms is assigned to non-interacting Mn sites, while additional components in the microsecond range appear with higher Mn doping, consistent with Mn clustering and resultant exchange coupling. Slower components are present in samples with low Mn doping, as well as strong afterglow, assigned to trapping on shallow traps followed by detrapping and subsequent trapping on Mn. Figure 1

Red-emitting manganese-doped aluminum nitride phosphor

We report high efficiency luminescence with a manganese-doped aluminum nitride red-emitting phosphor under 254nm excitation, as well as its excellent lumen maintenance in fluorescent lamp conditions, making it a candidate replacement for the widely deployed europium-doped yttria red phosphor. Solid-state reaction of aluminum nitride powders with manganese metal at 1900°C, 10atmN2 in a reducing environment results in nitrogen deficiency, as revealed diffuse reflectance spectra. When these powders are subsequently annealed in flowing nitrogen at 1650°C, higher nitrogen content is recovered, resulting in white powders. Silicon was added to samples as an oxygen getter to improve emission efficiency. NEXAFS spectra and DFT calculations indicate that the Mn dopant is divalent. From DFT calculations, the UV absorption band is proposed to be due to an aluminum vacancy coupled with oxygen impurity dopants, and Mn2+ is assumed to be closely associated with this site. In contrast with some previous reports, we find that the highest quantum efficiency with 254nm excitation (Q.E.=0.86±0.14) is obtained in aluminum nitride with a low manganese doping level of 0.06mol.%. The principal Mn2+ decay of 1.25ms is assigned to non-interacting Mn sites, while additional components in the microsecond range appear with higher Mn doping, consistent with Mn clustering and resultant exchange coupling. Slower components are present in samples with low Mn doping, as well as strong afterglow, assigned to trapping on shallow traps followed by detrapping and subsequent trapping on Mn.

Synthesis and spectral characterization of Sr4Al14O25:Eu2+/Dy3+ blue–green phosphorous powders by sol–gel method

Highly intense, long persistent Sr4Al14O25:Eu2+/Dy3+ phosphorous powders were prepared for the first time by sol–gel method under argon atmosphere. 2.5mol% of H3BO3 was added as fluxing agent. Characterization of the powders was carried out by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The average particle size of the fabricated phosphor powders was found to be 460nm in dispersed form in pure water. UV–Vis, steady-state and time resolved fluorescence spectroscopy techniques were used for spectral characterization of the powders. The phosphors exhibited two different emission bands at 449 and 550nm upon excitation at 400nm. It is observed that the position and the intensity of the emission band strongly depends on the excitation wavelength and shifts toward lower energy and intensity with increasing wavelength of the excition source. The broad band luminescence characteristics of the Sr4Al14O25:Eu2+/Dy3+ were observed at 492nm in the absence of the excitation source. The Sr4Al14O25:Eu2+/Dy3+ phosphor can be efficiently excited with the visible fraction of the light and show persistent luminescence, long and strong afterglow up to 35min after removal of the excitation source.

Luminescent Performance of the Long-Persistence Sr2MgSi2O7: Eu2+, Dy3+ Inorganic Nanofibers

Long-persistence silicate luminescent nanofibers doped with rare earths (Sr2MgSi2O7: Eu2+, Dy3+) were successfully prepared via electrospinning technique combined with calcination method, and long-lasting silicate phosphors (Sr2MgSi2O7: Eu2+, Dy3+) with the same stoichiometric proportion as the nanofibers were prepared by sol-gel method. The morphology, crystal structure, photoluminescence and thermoluminescence properties of the nanofibers compared with the phosphors were investigated. The average diameter of the Sr2MgSi2O7: Eu2+, Dy3+ luminescent nanofibers was 350 nm, and the whole shape of the nanofibers was consecutive which seemed like pearl necklace. The synthesis temperature of the Sr2MgSi2O7: Eu2+, Dy3+ luminescent nanofibers was 1100°C which lower 200°C than phosphors. The excitation spectrum of the nanofibers moved to short wavelength direction compared with the phosphors, and the nanofibers could reveal a bright blue light after been excited by UV light at 365 nm. The initial afterglow intensity of the nanofibers was 1.26 cd·m−2, and the afterglow decay curve of the nanofibers was similar to phosphors. Even though the depth of the traps of the luminescent nanofibers was shallower than phosphors, the nanofibers still presented strong afterglow intensity and long decay time.

Construction of cellulose-phosphor hybrid hydrogels and their application for bioimaging.

Bioimaging is a key technique for monitoring behavior and activity in vivo and plays an important role in the life science and medical fields. In the present work, for the first time, a new, safe cellulose based hybrid hydrogel was constructed from a cellulose solution containing rare-earth doped phosphor (PP) in an alkali/urea aqueous system using epichlorohydrin as a crosslinker. Its structure and properties were characterized by wide angle X-ray diffraction, FT-IR spectra, solid-state 13C NMR, field emission scanning electron microscopy, UV-vis spectroscopy, fluorescence spectra, and compression tests. The results indicated that the PP particles were tightly embedded in the macroporous cellulose matrix, which not only supplied cavities for PP immobilization through relatively strong intermolecular hydrogen bonding interactions, but also supplied the pore wall as a shell to protect the structure and character of PP. Thus, the cellulose/PP hybrid (CPH) hydrogels emitted relatively strong green fluorescence under a UV lamp, as well as high brightness and long-lasting afterglow. This could avoid harmful radiation in the body and improve signal resolution with lower cell autofluorescence interference. Notably, CPH with strong afterglow could be detected both under the skin and in the stomach with and without excitation light, showing promising prospects as a candidate for bioimaging. Moreover, the hybrid hydrogels exhibited good compressive strength and processability.

Thermoluminescence of NaCl:Cu sintered phosphors exposed to beta irradiation

NaCl:Cu pellet-shaped phosphors were synthesized through a sintering process. Some samples were exposed to beta irradiation in order to investigate their thermoluminescence properties and capabilities to be used in detecting and measuring ionizing radiation. The glow curves reveal at least four thermoluminescence peaks below 250°C, and a main one above 300°C when a 5°C/s heating rate is used. The lowest temperature peak vanishes in less than 3 min after irradiation, giving rise to an intense afterglow luminescence, potentially useful for in situ non-thermoluminescence dosimetry, and the next remains for about 3 h, but the high temperature one exhibits no important changes after that time. The thermoluminescence intensity increased as the radiation dose increased in the 0.417–25.0 Gy dose range. Because the position and the remarkable stability of the higher temperature peak, besides the strong afterglow produced by the fast decaying of the lower temperature peak, it is concluded that these phosphors are very suitable candidates to be used in both thermoluminescence and non thermoluminescence dosimetry of ionizing radiation, having advantages over monocrystals of similar composition. The synthesis route here followed can be reproduced in standard college laboratories, and thermoluminescence be measured in home-made systems, allowing design practices for interdisciplinary physics, chemistry electronics, and materials science students.

Gamma irradiation effects on the luminescence properties of SrBPO5: Sm

Samarium doped SrBPO5 phosphor was synthesized by a high temperature solid state reaction route and its luminescence properties were investigated before and after gamma irradiation. A photo-acoustic spectroscopic technique was used to record the excitation/absorption spectrum of the sample. Photoluminescence studies on the sample prior to gamma irradiation confirmed the presence of Sm3+ at an asymmetric site. After 2kGy of gamma irradiation, the sample showed strong afterglow without any external source that lasted for several minutes. Thermoluminescence (TSL) studies revealed the presence of glow peak at 323K for the system. Electron spin resonance (ESR) studies suggested the formation of borate and oxygen based radical centers in the gamma irradiated system. Detailed ESR–TSL correlation study confirmed the destruction of the oxygen radical to be responsible for the observed glow peak. Based on the findings, a probable mechanism was proposed for the glow peak and observed afterglow.

Trap Levels in Eu and other Rare‐Earth Ions Codoped CaAl2O4 Phosphors

Photoluminescence spectrum, trap depths, and densities of trapped carriers of CaAl2O4:Eu phosphor crystals doped with rare‐earth elements were studied using the thermally stimulated luminescence technique. Trap depths and densities of the specimens vary with rare‐earth elements doped as the auxiliary activators. Tm and Nd are found to be effective for the strong afterglow phosphorescence peaking at λ = 442 nm for several hours after the excitation. CaAl2O4:Eu phosphor crystals doped with Nd and Tm include high density of carriers trapped at E = 0.59 and 0.52 eV, respectively.

Red luminescence and persistent luminescence of Sr3Al2O5Cl2:Eu2+,Dy3+

The luminescence and persistent luminescence properties of Sr3Al2O5Cl2:Eu2+ and Sr3Al2O5Cl2:Eu2+,Dy3+ phosphors have been investigated. Both materials show d–f emission of Eu2+ in the orange/red spectral region around 615nm at room temperature. The temperature dependent emission spectra and decay curves of Eu2+ ions doped into Sr3Al2O5Cl2 are reported and discussed. Sr3Al2O5Cl2:Eu2+ shows considerable thermal quenching of its luminescence. It is also observed that the position of the emission band strongly depends on the temperature and shifts toward higher energy with increasing temperature, from 645nm at 77K to 594nm at 500K. Both, Sr3Al2O5Cl2:Eu2+ and Sr3Al2O5Cl2:Eu2+,Dy3+ show persistent luminescence. The persistent luminescence of Sr3Al2O5Cl2:Eu2+ is rather weak and lasts only for solely a few seconds, while the same material co-doped with Dy3+ shows longer and stronger afterglow.

Laser excited long lasting luminescence in CaAl2O4: Eu3+/Eu2+ + Nd3+ phosphor

The europium and neodymium oxides doped nano-structured calcium aluminate phosphor samples have prepared through combustion technique and their luminescence properties are studied using laser excitations. Samples prepared in open atmosphere showed the presence of both Eu3+ and Eu2+ states and their ratio changes with calcination temperature. Single Eu3+/Eu2+ ions doped sample has found to give broad emission at 450nm without the persistence glow while the Eu3++Nd3+ ions codoped sample has shown persistence glow at 450nm (Eu2+) on 355nm laser excitation. Wavelength selective excitations show that 266nm excitation gives the intense emissions from both Eu3+ and Eu2+ states with no afterglow but 355nm excitation gives negligible emission from Eu3+ ions and a strong afterglow at 450nm wavelength. The mechanism of wavelength dependent phosphorescence has been discussed. Studies on Stark splittings and their relative intensities in emission spectra of Eu3+ ions have shown that Eu3+ ion can be used as excellent probe of crystal structure.

Photoluminescence properties of europium and titanium co-doped BaZrO3 phosphors powders synthesized by the solid-state reaction method

In this paper, we reported on the obtention of a series of europium and titanium co-doped BaZrO3 phosphors, which could emit red-orange long afterglow, synthesized by the solid-state reaction method. The structures, morphology and photoluminescent properties of the all samples were characterized and analyzed by X-ray diffraction (XRD), Schottky field-emission scanning electron microscope (FE-SEM), photoluminescence (PL) and decay curves, respectively. The XRD analyses showed that the reflection of all prepared BaZrO3 powders was well indexed to cubic structure. The room-temperature excitation spectra monitored at 594nm consist of a broad band with the stronger excitation PL peak, which located at 260nm, and a series of narrow bands. A series of narrow bands from 4f→4f emission transitions of the 5D0 excited level to the 7FJ (J=0–4) levels of the Eu3+ ions were observed in the emission spectra excited at 260nm. The decay curves of samples well coincided with the sum of two exponential functions. Combining experimental results and theoretical analyzis, we proposed a corresponding novel afterglow mechanism, which reasonably explained the afterglow phenomenon of BaZrO3:Eu, Ti. The BaZrO3:Eu, Ti phosphors had stronger afterglow, better monochromaticity and longer decay time compared with BaZrO3:Eu phosphors. It implied that the Ti co-doping was an effectual and practical way to improve afterglow performance of BaZrO3-based phosphors.