Photostimulated Luminescence Research Articles

The long-term isothermal oxidation and cyclic oxidation performance of anodized Ti48Al2Nb2Cr alloy

The long-term isothermal oxidation and cyclic oxidation performance of the Ti48Al2Nb2Cr alloy anodized in NH4F containing electrolyte were investigated. After isothermal oxidation at 1000 °C and cyclic oxidation at 900 °C for 1000 h, the weight gains of the anodized Ti48Al2Nb2Cr alloys are 1.12 mg cm−2 and 0.48 mg cm−2, respectively. The excellent oxidation performance is ascribed to the fluorine effect. Raman and photo-stimulated luminescence spectra revealed that anodization impedes the formation of rutile and promotes the generation of α-Al2O3 at high temperatures. The Al2O3 and TiO2 formed during anodization act as crystal nucleus for the generation of α-Al2O3-based scale.

Site-Selective Occupancy of Mn2+ Enabling Adjustable Red/Near-Infrared Multimode Luminescence in Olivine for Dynamic Anticounterfeiting and Encryption

Transition metal Mn2+ ion activated luminescent materials with tunable visible emission and high color purity features are crucial for mondern lighting and displays and so forth. Herein, in contrast to the conventional visible emission of Mn2+, an olivine phosphor, Mg2GeO4:Mn2+, with adjustable red (centered at ∼ 650 nm)/NIR (centered at∼ 735 nm) emissions is demonstrated by doping Mn2+ ions into two different distorted octahedral MgO6 sites guided by theory simulation. By varying the doping content of Mn2+ ions, the red/NIR dual-wavelength emissions to a pure-NIR emission can be easily achieved in this system, and the luminescence properties are in good agreement with the theoretical analysis. Morevoer, when suitable defect traps are introduced in the band gap of Mg2GeO4 via Yb3+ ion codoping, adjustable red/NIR persistent luminescence and photostimulated luminescence are further realized in both Mg2GeO4:Mn2+,Yb3+ phosphor, and the ceramics. A reliable anticounterfeiting/dymamic information encryption technique is presented by the combination of as-prepared Mg2GeO4:Mn2+ and Mg2GeO4:Mn2+,Yb3+. This study not only provides a multimode luminescent material for dynamic anticounterfeiting and encryption, but also provides insights into the NIR emission of Mn2+.

A Temporal and Space Anti-counterfeiting Based on the Four-Modal Luminescent Ba2Zr2Si3O12 Phosphors.

Fluorescent anti-counterfeiting materials have been widely studied due to their high resolution and convenient identification by direct visualization of the color output. To date, the anti-counterfeiting technology of single ultraviolet excitation mode still has security problems because the single mode could be imitated easily. Here, we have successfully developed four modes of anti-counterfeiting from Eu2+ and Er3+ co-doped Ba2Zr2Si3O12 phosphors with photo, long persistent, photo-stimulated, and up-conversion luminescence behavior. The as-fabricated phosphors can emit an intense blue-green luminescence originating from the characteristic transition of Eu2+ ions and exhibit a blue-green long persistent luminescence phenomenon. Moreover, the enhancement of photo-stimulated luminescence that contributed to the effectively increased trap concentration is observed, along with the produced up-conversion phenomenon thanks to the introduction of Er3+ ions. Notably, the fluorescence rapidly changes from blue-green to stable green luminescence with the delay of excitation time under the excitation of a 980 nm laser diode. Herein, this work realizes the fast down- to up-conversion luminescence output over time, which provides the basis for its possible application in advanced multi-mode anti-counterfeiting.

Multi-mode readout via opto-mechano-photothermo-responsive luminescence from electron trapping material for optical information storage application

Optical storage material is one of the promising candidates for next generation of information memory medium owing to large capacity, reusable rewritable, and rapid response performance. However, as the typical optical storage medium, electron trapping materials (ETMs) are limited in applications of information preservation or optical display technology due to their single readout route relying on photostimulated luminescence (PSL). A crucial limitation to the feasibility of multi-mode optical information readout is the inevitable mismatch between trap depth and the energy of external stimuli. In this study, by introducing Bi3+ ions as intermediate levels between deep traps and emitters, we developed a LiTaO3:Tb3+/Bi3+ (LTO) material that can simultaneously response to optical, mechanical, and thermal stimuli efficiently, showing as multiple trap-controlling luminescence. The tantalate material was endowed with opto-mechano-responsive readout capacity when assembled with polymer matrix. Moreover, by utilizing LiCaYb0.5Nd0.5(WO4)3 microcrystals (LCYW) with near-infrared-induced photothermy property, we designed a LTO-LCYW bilayer composite film then achieved non-contact thermo-responsive readout of optical information via photothermo-stimulated luminescence. These findings provide a unique perspective for designing multi-mode responsive luminophors and photonic devices towards widespread applications, especially optical display, optical memory technology, and anticounterfeiting.

Crystal structure and optical performance analysis of a new type of persistent luminescence material with multi-functional application prospects

Persistent luminescence (PersL) materials, as environmentally friendly and energy-saving materials, have broad application prospects in many fields such as lighting, chemistry and even biomedicine. However, studies on the types, performances and mechanism of PersL materials are still insufficient, which significantly restricts their development and application. Under this consideration, we successfully synthesized a yellow PersL material CaSrGa4O8 (CSG). The crystal structure was studied in detail through Rotation Electron Diffraction (RED) and Powder X-ray Diffraction (PXRD). What’s more, by co-doping Mn2+ and Yb3+, the afterglow brightness of CSG could be increased by nearly 20 times, and the afterglow duration could reach more than 6 h. It is worth mentioning that the samples also have excellent performances in mechanical luminescence (ML), photostimulated luminescence (PSL) and cathodoluminescence (CL), which was also investigated systematically. Finally, an anti-counterfeiting label was designed by the samples to reveal the potential of their application in anti-counterfeiting. The results showed that our research not only provided a new candidate PersL material for multifunctional applications, but also gave good help for studying the physical and chemical properties of CSG.

Bi-Induced Photochromism and Photo-Stimulated Luminescence with Fast Photochromic Response for Multi-Mode Dynamic Anti-Counterfeiting and Optical Information Storage

Bi-Induced Photochromism and Photo-Stimulated Luminescence with Fast Photochromic Response for Multi-Mode Dynamic Anti-Counterfeiting and Optical Information Storage

Thermally grown oxide formation on Ni2Al3 aluminide coating: The effect of nanocrystalline nickel film on oxide scale adhesion

The Ni2Al3 coatings were prepared by aluminizing with and without nanocrystalline (NC) Ni film using the pack cementation process for 5 h at 620 °C. After oxidation at 900 °C, the results demonstrate that the alumina formed on two Ni2Al3 coatings composed of θ-Al2O3 on the basis of investigations of scanning electron microscopy (SEM), x-ray diffraction (XRD) and photo-stimulated luminescence spectroscopy (PSLS). The transmission electron microscopy (TEM) investigations combined with the electron diffraction pattern revealed that a small grain of α-Al2O3 nucleated on the Ni2Al3 coating with Ni film at the alumina scale/coating interface. Moreover, the Ni2Al3 coating with Ni film, in comparison to Ni2Al3 coating without Ni film control the size and density of the cavities formation at the scale/coating interface resulted in better adhesion of the alumina scale on aluminide.

A color-tunable persistent luminescence material LiTaO3:Pr3+ for dynamic anti-counterfeiting

In this work, an original color-tunable persistent luminescence (PersL) phosphor based on Pr3+ doped LiTaO3 (LTO) was realized. The PersL emission can be modulated from pale yellow to deep orange-red merely by changing the concentration of Pr3+, which attributed to the concentration quenching resulted from the cross-relaxation (CR) effect. Thermoluminescence (TL) analysis shows that the continuous shallow traps (0.668–0.8 eV) are suitable for PersL. Moreover, it also exhibits excellent photostimulated luminescence (PSL) performance owing to the presence of stable deep traps of 0.916 eV. A possible PersL mechanism of LTO:Pr3+ is put forward to explain this phenomenon. Finally, inspired by this multicolor PersL feature, a quick response code (QR-code) and an arrow pattern are developed, revealing that LTO:Pr3+ is an ideal material for dynamic anti-counterfeiting. Our work is designed to promote the practical applications of PersL materials in information security areas.

The role of boric acid in optical information storage properties in Eu doped BaSi2O5

Optical information storage technology is emerging, therefore materials suitable for optical write-in and read-out are in demand. In this study the influence of boric acid addition during synthesis on the optical information storage properties of BaSi2O5:Eu material, that has been recently offered as a perspective material for this application. A thorough investigation is carried out to establish the relationship between boric acid addition, phase composition and photostimulated luminescence performance of the samples. The present work demonstrates the influence of the boric acid addition on the trapping center distribution in the material, thus leading to the improvement of photostimulated luminescence intensity. This can lead to the optimization of BaSi2O5:Eu material for optical information storage.

Photostimulated luminescence in Tl-doped NH4Br translucent ceramics synthesized by SPS

We have prepared Tl-doped NH4Br translucent ceramics by spark-plasma sintering and evaluated their photoluminescence (PL) and photostimulated luminescence (PSL) properties. In PL, two luminescence peaks appeared due to 3P1 → 1S0 transitions of Tl+ and off-center self-trapped excitons (STEs) localized around Tl+ in all the samples. In PSL, the 0.1%–3% Tl-doped samples showed luminescence related to the off-center STEs around 500 nm by stimulation light at 630 nm. When correlations between exposure dose and PSL intensity were examined, we confirmed that the 0.1%–1% and 3% Tl-doped samples showed linear responses over ranges of 10–10 000 and 1–10 000 mGy, respectively.

Development of a novel microbiological method for detection of gamma irradiated spices

Spices are food additives that are used in many different areas of food technology. Most of the spices contain essential oils sensitive to thermal degradation processes. Therefore, an alternate method of decontamination, other than thermal, should be used so that the microbial safety of the spices is ensured. This study was focused on the evaluation of the effect of ionizing radiation, known as radurization, on microbiological safety in samples of red pepper, black pepper, and stinging nettle, from North Macedonia. Samples were irradiated by 60Co γ-rays. The possibility for development of a novel, shortened microbiological method was investigated. The conventional agar plate method was used, as a standard microbiological method, in order to evaluate the effect of irradiation on the microbiological safety of the food. The red pepper and the stinging nettle did not show any microbial growth when inoculated on both growth media, after being irradiated. Additionally, the photostimulated luminescence and thermoluminescence method were used as physical methods. By comparing the two glow curves for the glow ratio, the obtained values are greater than 0.1, which confirms that the samples have been irradiated.

Near‐Infrared Persistent Luminescence and Trap Reshuffling in Mn4+ Doped Alkali‐Earth Metal Tungstates

AbstractNear‐infrared persistent luminescent materials have great potential for in vivo bioimaging and night‐vision surveillance due to their long‐lasting autofluorescence‐free emission through deep tissues and multicycle photostimulated luminescence by releasing energy from captured traps using high‐intensity 808 or 980 nm lasers. However, phosphors combining both near‐infrared persistent luminescence and photostimulated luminescence are found mostly in chromium doped gallates hosts, other emitters are rarely reported. Herein, a new material system with near‐infrared persistent luminescence is achieved in tetravalent manganese doped double‐perovskite alkali‐earth metal tungstates via the aliovalent substitution of calcium ions with lanthanum ions. Persistent luminescence can be generated via X‐ray irradiation, providing great promise in long‐term deep‐tissue ultrasensitive imaging, information storage, and X‐ray detection. Photostimulated detrapping is successfully demonstrated using a common 420 nm light emitting diode instead of a high‐intensity 808 or 980 nm laser. The traps distribution is proved to be reshuffled upon this laser‐free visible light stimulation. Reshuffling of trap distributions upon visible light stimulation may be promising for optical information storage applications. This work is expected to broaden the range of near‐infrared persistent material systems and provides new insights into manipulating photostimulated traps via laser‐free light stimulation.

Multi-responsive deep-ultraviolet emission in praseodymium-doped phosphors for microbial sterilization.

Perusing multimode luminescent materials capable of being activated by diverse excitation sources and realizing multi-responsive emission in a single system remains a challenge. Herein, we utilize a heterovalent substituting strategy to realize multimode deep-ultraviolet (UV) emission in the defect-rich host Li2CaGeO4 (LCGO). Specifically, the Pr3+ substitution in LCGO is beneficial to activating defect site reconstruction including the generation of cation defects and the decrease of oxygen vacancies. Regulation of different traps in LCGO:Pr3+ presents persistent luminescence and photo-stimulated luminescence in a synergetic fashion. Moreover, the up-conversion luminescence appears with the aid of the 4f discrete energy levels of Pr3+ ions, wherein incident visible light is partially converted into germicidal deep-UV radiation. The multi-responsive character enables LCGO:Pr3+ to response to convenient light sources including X-ray tube, standard UV lamps, blue and near-infrared lasers. Thus, a dual-mode optical conversion strategy for inactivating bacteria is fabricated, and this multi-responsive deep-UV emitter offers new insights into developing UV light sources for sterilization applications. Heterovalent substituting in trap-mediated host lattice also provides a methodological basis for the construction of multi-mode luminescent materials.

Tailored Luminescence Output of Bi3+-Doped BaGa2O4 Phosphors with the Assistance of the Introduction of Sr2+ Ions as Secondary Cations.

In this work, a tunable luminescence color from yellow to orange of photoluminescence (PL), long persistent luminescence (LPL), and photostimulated luminescence (PSL) is successfully achieved in BaGa2O4:Bi3+ phosphors with the introduction of Sr2+ ions as secondary cations. It is confirmed that broad-band emissions located at 500 and 600 nm originate from the occupation of Bi3+ ions at different lattice sites in the BaGa2O4 host matrix. The replacement of Sr2+ for Ba2+ ions makes the emission red-shift from 600 to 650 nm; moreover, two additional emissions appeare at 743 and 810 nm due to the occupational preference of Bi3+ ions at Ga3+ sites. Furthermore, the doped Sr2+ ions promote the reconstruction of the trapping centers, which conduces to the fundamental improvement of the optical storage capacity behavior of Bi3+-doped phosphors. Our results clarify the dependence of the luminescence performance on the crystal sites of Bi3+ ions with fascinating broad-band emissions in the BaGa2O4:0.01Bi3+ host matrix and will benefit the design and exploration of Bi3+-doped solid solutions for optical storage applications.

European inter-comparison studies as a tool for perfecting irradiated food detection methods

Abstract In this paper, we present the results of inter-comparison studies on identification of irradiated food carried out by the leading European laboratories from 1991 to 2018. In 1990s, the Federal Institute for Health Protection of Consumers and Veterinary Medicine in Germany played the leading role in the organization of the inter-laboratory tests on this subject. At the beginning of the present century, the Spanish Agency for Food Safety and Nutrition and Food National Spanish Centre took over this role. In total, 47 international tests were carried out in which nearly 500 samples of alimentary products were analysed in 37 laboratories from 14 European countries. The tests were aimed at proving the reliability of analytical methods – thermoluminescence (TL), photostimulated luminescence (PSL), and electron paramagnetic resonance (EPR) spectroscopy – for identification of specific irradiated food products and to control the analytical skills and experience of participating laboratories. The results made possible a discussion on why some irradiated food samples are more difficult for identification. In general, the tests showed that TL measurements of products such as herbs, nuts, peppers, and raisins, and EPR studies of fish and chicken bones, fresh strawberries, and dried fruits could be used as reliable control methods. The challenge that control laboratories are facing now, is related to the identification of complex food products such as diet supplements or biopharmaceuticals, in which only some additives are irradiated.

Development of a storage phosphor imaging system for proton pencil beam spot profile determination.

Accurate two-dimensional (2D) profile measurements at submillimeter precision are necessary for proton beam commissioning and periodic quality assurance (QA) purposes and are currently performed at our institution with a commercial scintillation detector (Lynx PT) with limited means for independent checks. The purpose of this work was to create an independent dosimetry system consisting of an in-house optical scanner and a BaFBrI:Eu2+ storage phosphor dosimeter by: (a) determining the optimal settings for the optical scanner, (b) measuring 2D proton spot profiles with the storage phosphors, and (c) comparing them to similar measurements using a commercial scintillation detector. An in-house 2D laboratory optical scanner was constructed and spatially calibrated for accurate 2D photostimulated luminescence (PSL) dosimetry. Square 5×5cm2 BaFBrI:Eu2+ dosimeter samples were uniformly irradiated with line scans performed to determine the physical and electronic scanner settings resulting in the highest signal-to-noise ratios (SNR) at a sub-millimeter spatial resolution. The resultant spatial resolution of the scanner was then quantitatively assessed by measuring (a) line pairs on a standard X-ray lead bar phantom and (b) modulation transfer functions. Following this, 2D proton spot profiles from a Mevion S250i Hyperscan proton unit were obtained at 1, 10, 20, 30, 40, and 50 monitor unit (MU) settings at maximum energy (E0 =227.1MeV) and compared to baseline profiles from a commercial scintillation detector, where 1MU is calibrated to deliver 1Gy absolute proton dose-to-water under reference conditions, that is, 41×41 proton spots uniformly spaced by 0.25cm within a 10×10cm2 square field size at maximum energy (227.1MeV) in water at depth of 5cm at isocenter. The dosimetric system's sensitivities to (a) ±1mm positional shifts and (b) ±0.3mm beam lateral spread changes were quantitatively evaluated through a Gaussian fitting of the crossline and inline plots of the respective artificially shifted beam profiles. The physical scanner settings of (a) Δτ=27ms time interval between data samples, (b) vx =1.235cm/s scanning speed, (c) 1% laser transmission (0.02mW power) and (d) (Δx, Δy)=(0.33, 0.50mm) pixel sizes with electronic settings of (a) 300 microseconds time constant, (b) normal dynamic reserve, (c) 24dB/oct low pass filter slope, and (d) 160Hz chopping frequency resulted in the highest SNR while maintaining sub-millimeter spatial resolution. The BaFBr0.85 I0.15 :Eu2+ storage phosphor dosimeters were linear from 1 to 50MU and their profiles did not saturate up to 150MU. The scanner was able to detect lateral displacements of ±1mm in both the crossline and inline directions and ±0.3mm beam spread changes that were artificially introduced by varying the incident proton energy. Specific to our proton unit, proton energy changes of ±1MeV can also be detected indirectly via beam spread measurements. Our combined dosimetric system including an in-house laboratory optical scanner and reusable BaFBr0.85 I0.15 :Eu2+ storage phosphors demonstrated a sufficient spatial resolution and dosimetric accuracy to support its use as an independent proton spot measurement dosimeter system. Its wide dynamic range allows for other versatile applications such as proton halo measurements.

Organic photostimulated luminescence associated with persistent spin-correlated radical pairs

Photostimulated luminescence allows energy or data to be stored and released using electromagnetic waves as both the input and output, and has attracted considerable interest in the fields of biomedical and information technologies. However, this phenomenon is mostly limited to solid inorganic materials. Here, we report photostimulated luminescence from purely organic blend films, composed of electron donor, acceptor, and trap/emitter molecules. Charges in the films are accumulated as radical ions by ultraviolet light irradiation and then extracted by near-infrared light irradiation. Even after storage in the dark for one week they produce visible light with good repeatability, color tunability, and are responsive to weak external magnetic fields. These findings might broadly impact existing applications and provide new prospects for innovative flexible devices.

Multicomponent garnet phosphor (LuYGd)(Al4Ga)O12:Ce3+,V3+: trap modulation via reductive gas annealing and an optical information storage property

Annealing treatments are an effective strategy to modulate trap depth and trap concentration in electronic materials. Herein, we have found that annealing in a weak reducing atmosphere is a good way to tailor the trap depth and trap concentration of the (LuYGd)(Al4Ga)O12:Ce3+,V3+ multicomponent phosphor. The characterization results show that the annealing atmosphere has no effect on the crystal structure and the photoluminescence peak position, but strengthens the trap depth and trap concentration. Especially, after annealing in a weak reducing atmosphere, the thermoluminescence (TL) integrated area of the phosphor is 7.46 times that of the unannealed phosphor, and the TL peaks obviously shift to a higher temperature region, which could be promoted to enhance optical information storage properties. Moreover, the peak position of photo-stimulated luminescence (PSL) is consistent with that of photoluminescence (PL), indicating that (LuYGd)(Al4Ga)O12:Ce3+,V3+ phosphor annealed in a weak reducing atmosphere possesses optical information read-in and read-out characteristics, and suggests that the multicomponent phosphor is a good candidate for optical information storage materials.

Emission from Storage Phosphors That Glow Even in Bright Ambient Light

Light-emission phenomena of storage phosphors have received widespread attention, provoking the continuous developments of persistent luminescence, photostimulated luminescence, and mechanoluminescence. In the study and application of storage phosphors, as a matter of experience, it is always necessary to avoid or eliminate ambient light. It is the requirement for ambient darkness that is hindering the further development of storage phosphors under different ambient conditions. Here, we report an interesting glow phenomenon of storage phosphors in bright ambient light by introducing a concept termed ambient stimulated emission, in which the ambient temperature and ambient lighting can simultaneously release energy stored in the storage phosphors and lead to long-lasting emissions beyond the visible spectrum. As a proof of concept, we focus our discussion on an x-ray-charged ${\mathrm{La}\mathrm{Mg}\mathrm{Al}}_{11}{\mathrm{O}}_{19}:{\mathrm{Gd}}^{3+}$ phosphor, which exhibits ambient stimulated emission in the ultraviolet-B region, with increased initial light emission when the phosphor is exposed to ambient illumination instead of dark conditions. The ambient-stimulated-emission performances are found to depend on the illuminance and spectral distribution of ambient light. Moreover, our study indicates that the glow phenomenon in bright ambient light commonly appears in various storage phosphors, involving ultraviolet and infrared phosphors. The introduction of ambient stimulated emission brings different insights to luminescence research and offers approaches to further learn about and utilize storage phosphors.

Effective red-orange luminescence and energy transfer from Gd3+ to Eu3+ in lithium gadolinium magnesium borate for optical devices

This work focuses on the luminescence properties of Eu2O3-doped borate glasses developed by the high-temperature-melting method. The appropriate spectroscopic methods have been used to selectively analyze absorption, excitation, energy transfer, and photo-stimulated luminescence (PSL). The parameters, viz. oscillator strengths, stimulated emission cross-sections, radiative transition probability, and branching ratios, essential for luminescence, are extracted both without and with thermal correction applying to 7F0 → 5D2 and 7F6 by using the theoretical Judd Ofelt (JO) model. By employing the IH model to the decay kinetics, the dipole-dipole interaction mechanism is evaluated. The color chromaticity confirms the red-orange luminescence of the prepared glasses. We observe significant changes in the Gd3+: 6P7/2–8S7/2 and Eu3+:5Do–7F2 luminescence which is attributed to the energy transfer from the 6P7/2 state of the Gd3+ to 5Do of the Eu3+. These results recommend these glasses for lasers and other optical device applications.