Storage Phosphor Research Articles

Advanced Intelligent Anti‐Counterfeiting in a Memory Storage Phosphor Through Response of Charge Carriers to Temperature

AbstractPersistent phosphor as a printing anti‐counterfeiting material has attracted strong attention owing to its inherent luminescent decay process and multi‐mode luminescence characteristics under external field stimulation. However, the dynamic persistent luminescence (PersL) pattern of a single material is only manifested in color changes and still faces the problem of being easily decrypted. Herein, a multi‐color luminescent material with a wide range distribution of traps is developed, which can emit strong white PersL. In addition, the phosphors show an intelligent response of thermo‐stimulated luminescence to ambient temperature via recalling the charging temperature of the traps. The PersL mechanism is proposed based on electron transfer between PbO6 and TbO6 octahedrons through the O bridging. Based on the intelligent response of thermo‐stimulated luminescence to temperature, high‐throughput multi‐channel luminescence anti‐counterfeiting can be achieved on a single phosphor recording layer. This study not only provides further insights into the PersL mechanism, but also opens a new door for constructing intelligent responsive anti‐counterfeiting materials.

Deep-trap ultraviolet persistent phosphor for advanced optical storage application in bright environments

Extensive research has been conducted on visible-light and longer-wavelength infrared-light storage phosphors, which are utilized as promising rewritable memory media for optical information storage applications in dark environments. However, storage phosphors emitting in the deep ultraviolet spectral region (200–300 nm) are relatively lacking. Here, we report an appealing deep-trap ultraviolet storage phosphor, ScBO3:Bi3+, which exhibits an ultra-narrowband light emission centered at 299 nm with a full width at half maximum (FWHM) of 0.21 eV and excellent X-ray energy storage capabilities. When persistently stimulated by longer-wavelength white/NIR light or heated at elevated temperatures, ScBO3:Bi3+ phosphor exhibits intense and long-lasting ultraviolet luminescence due to the interplay between defect levels and external stimulus, while the natural decay in the dark at room temperature is extremely weak after X-ray irradiation. The impact of the spectral distribution and illuminance of ambient light and ambient temperature on ultraviolet light emission has been studied by comprehensive experimental and theoretical investigations, which elucidate that both O vacancy and Sc interstitial serve as deep electron traps for enhanced and prolonged ultraviolet luminescence upon continuous optical or thermal stimulation. Based on the unique spectral features and trap distribution in ScBO3:Bi3+ phosphor, controllable optical information read-out is demonstrated via external light or heat manipulation, highlighting the great potential of ScBO3:Bi3+ phosphor for advanced optical storage application in bright environments.

Characterization of the image plate multi-scan response to mono-energetic x-rays.

Image plates (IPs), or phosphor storage screens, are a technology employed frequently in inertial confinement fusion (ICF) and high energy density plasma (HEDP) diagnostics because of their sensitivity to many types of radiation, including, x rays, protons, alphas, beta particles, and neutrons. Prior studies characterizing IPs are predicated on the signal level remaining below the scanner saturation threshold. Since the scanning process removes some signal from the IP via photostimulated luminescence, repeatedly scanning an IP can bring the signal level below the scanner saturation threshold. This process, in turn, raises concerns about the signal response of IPs after an arbitrary number of scans and whether such a process yields, for example, a constant ratio of signal between the nth and n + 1st scan. Here, the sensitivity of IPs is investigated when scanned multiple times. It is demonstrated that the ratio of signal decay is not a constant with the number of scans and that the signal decay depends on the x-ray energy. As such, repeatedly scanning an IP with a mixture of signal types (e.g., x ray, neutron, and protons) enables ICF and HEDP diagnostics employing IPs to better isolate a particular signal type.

Electrochemical and photoluminescence properties of Ce3+ doped copper aluminate nanoparticles

In this communication, for the first of its kind, CuAl2O4 doped with Ce3+ (1-9 mol %) are syn- thesized by solution combustion method using Aloe Vera gel as a reducing agent. The as-formed sample was calcined at 500° C for 3 hours, followed by characterization. The addition of dopants to the copper aluminate matrix didn't alter the crystal structure of the host matrix. Bragg reflec- tions confirm the formation of the cubic phase and also absence of other impurities. The surface morphology consists of nanorods arranged one above the other. The estimated crystallite size was found to decrease from 12 to 9 nm whereas, the direct energy band gap increases from 2.84 to 3.02 eV with an increase in dopant concentration. Under λex = 305 nm excitation, photoluminescence (PL) emission spectra have a high intense peak at 553 nm along with a less intense peak at 472 nm. The peak at 553 nm can be attributed to the existence of oxygen vacancies which arise due to the transition of an electron from the 2D3/2→2F7/2 of Ce3+, however, the peak observed at 472 nm results from the transition of ionized oxygen vacancies (VO) to the valence band caused by the 2D3/2→2F5/2 transition. The CIE coordinates lie well within the green region with 5758 K aver- age CCT. Further, Cyclic voltammetry analysis was conducted to investigate oxidation and redox peaks, while electrochemical impedance spectroscopy provided insights into ion transport kinetics. Specific capacitance values ranging from 29 to 59 F/g were obtained for CuAl2O4:Ce(1-9 mol %) NPs. These findings suggest potential applications for the synthesized material in areas such as display technology as a green nano phosphor and energy storage materials.

Trap engineering in bismuth activated NaLu(Gd)GeO4 persistent phosphors by doping Ln3+

Persistent phosphors, as a promising material for information storage and encryption, have garnered considerable attention owing to their rapid access and low-energy consumption. However, the lack of effective trap control in storage phosphors has resulted in limited storage capacity. In this study, we have prepared a series of NaLu(Gd)GeO4:Bi3+,Ln3+ (Ln = Eu, Tb, Dy, Pr, Sm, Er, Nd, Ho, Tm, and Yb) materials exhibiting tunable multimode and multicolor stimuli-responsive luminescence. The enhanced thermo-stimulated luminescence of five times is obtained in NaLuGeO4:Bi3+,Eu3+ relative to NaLuGeO4:Bi3+, where Bi3+ not only serves as the luminescent center but also as the hole trap center, and trace amounts of Eu3+ act as electron traps to form stable electron-hole pair traps together with Bi3+ hole traps. We propose a new method to improve trap density by constructing electron-hole pair traps via utilizing Bi3+ and Ln3+ as both trap makers and luminescence centers. Density functional theory calculations provide detailed information on the band structures of the matrix and electronic properties, which has confirmed the types of traps and then supports persistent luminescence mechanisms. Particularly, our phosphors are used as optical storage medium for multilevel optical data recording in a single physical layer through managing traps via setting the temperature. This study provides valuable insights for the design and fabrication of next-generation optical information storage and encryption materials.

Imaging Plate radiography for non-destructive determination of the radioactivity fraction in “hot” particles

In the environment, artificial radionuclides exist in various mobile and non-mobile forms. One of the most kinetically stable radionuclides forms is so-called “hot” particles which could be found and extracted from soil samples using laser-scanned radiography with Imaging Plate. Method limitations are the signal fading over time and the lack of information about the quantitative capabilities of the method. In this work, the correlation between photostimulated luminescence (Cyclone Storage Phosphor System, PerkinElmer) and the radioactivity of various sources, their radiation energy, and exposure duration was determined. The fading of photostimulated luminescence over exposure time was studied for different radionuclides. As a result of the Imaging Plate Radiography calibration, the possibility of a semi-quantitative analysis of radioactively contaminated samples using Imaging Plate was confirmed. To carry out the comparative analysis of the samples from nuclear legacy sites a non-destructive tool has been developed for express definition of the fraction of radioactivity stored in “hot” particles. The application of this technique is demonstrated by examples of three different soil samples with "hot" particles.

Micro-Inclusion Engineering via Sc Incompatibility for Luminescence and Photoconversion Control in Ce3+-Doped Tb3Al5-xScxO12 Garnet.

Aluminum garnets display exceptional adaptability in incorporating mismatching elements, thereby facilitating the synthesis of novel materials with tailored properties. This study explored Ce3+-doped Tb3Al5-xScxO12 crystals (where x ranges from 0.5 to 3.0), revealing a novel approach to control luminescence and photoconversion through atomic size mismatch engineering. Raman spectroscopy confirmed the coexistence of garnet and perovskite phases, with Sc substitution significantly influencing the garnet lattice and induced A1g mode softening up to Sc concentration x = 2.0. The Sc atoms controlled sub-eutectic inclusion formation, creating efficient light scattering centers and unveiling a compositional threshold for octahedral site saturation. This modulation enabled the control of energy transfer dynamics between Ce3+ and Tb3+ ions, enhancing luminescence and mitigating quenching. The Sc admixing process regulated luminous efficacy (LE), color rendering index (CRI), and correlated color temperature (CCT), with adjustments in CRI from 68 to 84 and CCT from 3545 K to 12,958 K. The Ce3+-doped Tb3Al5-xScxO12 crystal (where x = 2.0) achieved the highest LE of 114.6 lm/W and emitted light at a CCT of 4942 K, similar to daylight white. This approach enables the design and development of functional materials with tailored optical properties applicable to lighting technology, persistent phosphors, scintillators, and storage phosphors.

Indirect evidence of Bi3+ valence change and dual role of Bi3+ in trapping electrons and holes for multimode X-ray imaging, anti-counterfeiting, and non-real-time force sensing

Discovering bismuth based smart materials that can respond to thermal, mechanical, and wide range X-ray to infrared photon excitation remains a challenge. Such materials have various uses like in advanced information encryption. In this work, valence state change between Bi2+, Bi3+, and Bi4+, and the dual role of Bi3+ in trapping electrons and holes have been studied in Bi3+ or/and Ln3+ (Ln=Tb or Pr) doped LiScGeO4 family of compounds by vacuum referred binding energy (VRBE) diagram construction, thermoluminescence, and spectroscopy. Electron release from Bi2+ has been evidenced. It can be used to experimentally determine the VRBE in the Bi2+ 2P1/2 ground state and to realize Bi3+ negative quenching luminescence. Particularly, a new force induced charge carrier storage phenomenon has been discovered for non-real-time force recording. Wide range of emission tailorable afterglow, unique Bi3+ ultraviolet-A, white, and infrared afterglow have been demonstrated by using Bi3+ as a hole trapping and recombination center and using energy transfer processes from Bi3+ to Tb3+, Pr3+, Dy3+, or Cr3+. Proof-of-concept advanced anti-counterfeiting, information encryption, and X-ray imaging will be demonstrated. This work not only develops smart storage phosphors, but more importantly unravels the valence change between Bi2+, Bi3+, or Bi4+ and how it can affect the trapping and release of charge carriers with thermal, optical, or mechanical excitation. This work therefore can promote the discovery and development of Bi3+ based smart materials for various applications.

Inorganic metal oxide material BaSiO3:Eu2+ for convenient 3D X-ray imaging

X-ray storage phosphors are found wide-ranging applications in medical diagnosis, nondestructive testing and X-ray imaging. However, designing X-ray storage phosphors with high electron storage capacity still poses a daunting challenge. In this study, we designed a fluorescent powder based on Eu2+-doped BaSiO3, demonstrating excellent optical information storage characteristic. Under high-energy X-ray filling, shallow traps exhibit low electron capacity and only produce weak afterglow, which greatly helps to minimize the impact of afterglow on the image quality during X-ray imaging. In addition, the deep traps at 1.01 eV filled with high-energy X-ray allow the material to store information for a long time. The crystal structure, photoluminescence (PL) and thermoluminescence (TL) spectra were studied systematically. The electron trapping properties of the material were analyzed using TL spectroscopy. Finally, we fabricated a flexible film with phosphors, the flexible film has been utilized to demonstrate high-quality real-time X-ray imaging and achieve time-delayed X-ray imaging of curved objects, such as flexible circuit boards.

Unveiling the influence of ambient lighting on stimulating ultraviolet luminescence of deep-trap phosphors

Glow-in-the-daylight is a fascinating luminescence phenomenon displayed by certain storage phosphors that emit ultraviolet light upon being stimulated by ambient lighting. In this study, we investigate the influence of indoor lighting on the glow-in-the-daylight emission of a co-doped garnet phosphor, Y3Al5O12:Pr3+,Eu3+, known for its deep trap that effectively retains energy. Our experimental results demonstrate an interesting observation that, following x-ray radiation at room temperature, this phosphor exhibits negligible persistent luminescence in darkness but emits intense ultraviolet light peaking at 318 nm under indoor lighting conditions. This emphasizes the crucial role played by ambient lighting in releasing stored energy. Our findings not only shed light on the influence of indoor illumination dose and spectral distribution on the persistently stimulated luminescence but also expand our exploration to various ultraviolet phosphors with deep traps, with the aim of uncovering novel materials applicable in glow-in-the-daylight scenarios.

Charge carrier trapping management in Bi3+ and lanthanides doped Li(Sc,Lu)GeO4 for x-ray imaging, anti-counterfeiting, and force recording

Discovering energy storage materials with rationally controlled trapping and de-trapping of electrons and holes upon x-rays, UV-light, or mechanical force stimulation is challenging. Such materials enable promising applications in various fields, for instance in multimode anti-counterfeiting, x-ray imaging, and non-real-time force recording. In this work, photoluminescence spectroscopy, the refined chemical shift model, and thermoluminescence studies will be combined to establish the vacuum referred binding energy (VRBE) diagrams for the LiSc1−xLuxGeO4 family of compounds containing the energy level locations of Bi2+, Bi3+, and the lanthanides. The established VRBE diagrams are used to rationally develop Bi3+ and lanthanides doped LiSc1−xLuxGeO4 storage phosphors and to understand trapping and de-trapping processes of charge carriers with various physical excitation means. The thermoluminescence intensity of x-ray irradiated LiSc0.25Lu0.75GeO4:0.001Bi3+,0.001Eu3+ is about two times higher than that of the state-of-the-art x-ray storage phosphor BaFBr(I):Eu2+. Particularly, a force induced charge carrier storage phenomenon appears in Eu3+ co-doped LiSc1−xLuxGeO4. Proof-of-concept non-real-time force recording, anti-counterfeiting, and x-ray imaging applications will be demonstrated. This work not only deepens our understanding of the capturing and de-trapping processes of electrons and holes with various physical excitation sources, but can also trigger scientists to rationally discover new storage phosphors by exploiting the VRBEs of bismuth and lanthanide levels.

Phosphors and Scintillators in Biomedical Imaging

Medical imaging instrumentation is mostly based on the use of luminescent materials coupled to optical sensors. These materials are employed in the form of granular screens, structured crystals, single transparent crystals, ceramics, etc. Storage phosphors are also incorporated in particular X-ray imaging systems. The physical properties of these materials should match the criteria required by the detective systems employed in morphological and functional biomedical imaging. The systems are analyzed based on theoretical frameworks emanating from the linear cascaded systems theory as well as the signal detection theory. Optical diffusion has been studied by different methodological approaches, such as experimental measurements and analytical modeling, including geometrical optics and Monte Carlo simulation. Analysis of detector imaging performance is based on image quality metrics, such as the luminescence emission efficiency (LE), the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE). Scintillators and phosphors may present total energy conversion on the order of 0.001–0.013 with corresponding DQE in the range of 0.1–0.6. Thus, the signal-to-noise ratio, which is crucial for medical diagnosis, shows clearly higher values than those of the energy conversion.

Micro-columnar CsBr:Eu storage phosphor for high-efficiency high energy photon radiography panels

Micro-columnar CsBr:Eu storage phosphor for high-efficiency high energy photon radiography panels

Manipulation of Shallow-Trap States in Halide Double Perovskite Enables Real-Time Radiation Dosimetry.

Storage phosphors displaying defect emissions are indispensable in technologically advanced radiation dosimeters. The current dosimeter is limited to the passive detection mode, where ionizing radiation-induced deep-trap defects must be activated by external stimulation such as light or heat. Herein, we designed a new type of shallow-trap storage phosphor by controlling the dopant amounts of Ag+ and Bi3+ in the host lattice of Cs2NaInCl6. A distinct phenomenon of X-ray-induced emission (XIE) is observed for the first time in an intrinsically nonemissive perovskite. The intensity of XIE exhibits a quantitative relationship with the accumulated dose, enabling a real-time radiation dosimeter. Thermoluminescence and in situ X-ray photoelectron spectroscopy verify that the emission originates from the radiative recombination of electrons and holes associated with X-ray-induced traps. Theoretical calculations reveal the evolution process of Cl-Cl dimers serving as hole trap states. Analysis of temperature-dependent radioluminescence spectra provides evidence that the intrinsic electron-phonon interaction in 0.005 Ag+@ Cs2NaInCl6 is significantly reduced under X-ray irradiation. Moreover, 0.025 Bi3+@ Cs2NaInCl6 shows an elevated sensitivity to the accumulated dose with a broad response range from 0.08 to 45.05 Gy. This work discloses defect manipulation in halide double perovskites, giving rise to distinct shallow-trap storage phosphors that bridge traditional deep-trap storage phosphors and scintillators and enabling a brand-new type of material for real-time radiation dosimetry.

The Effect of Different Storage Conditions and Scan Delays on the Mean Gray Value (MGV) on Photostimulable Storage Phosphor (PSP) Plate Images

Amaç: Bu çalışmanın amacı, ışıkla uyarılabilen fosfor (Photostimulable Storage Phosphor, PSP) plakalarının ışınlama-tarama süreçleri arasındaki farklı tarama gecikmeleri (bekletme süresi) ve saklama koşullarının görüntülerindeki Ortalama Gri Değer (OGD) değişimine etkisini değerlendirmekti. Gereç ve Yöntem: Saklama koşuluna göre oluşturulan dört grupta [Tek Kılıf Aydınlık (TKA), Tek Kılıf Karanlık (TKK), Tek Kılıf Karton Aydınlık (TKKA), Tek Kılıf Karton Karanlık (TKKK)] farklı bekletme sürelerinde toplam 40 görüntü elde edildi. ImageJ (National Institutes of Health, Bethesda, MD) programı ile görüntülerin OGD’leri ölçüldü. Saklama koşullarını karşılaştırmak için tek yönlü, bekletme sürelerini karşılaştırmak için iki yönlü tekrarlı ölçümlü ANOVA testleri kullanıldı. Her bir gruptaki bekletme süreleri ile 0 dk. (altın standart) OGD’lerin karşılaştırılması için eşleştirilmiş örneklemler t-testi uygulandı. p<0.05 istatistiksel olarak anlamlı kabul edildi. BULGULAR: On dk. ile altın standart arasındaki OGD farkı sadece TKA grubunda istatistiksel olarak anlamlıydı (p<0.05). Herhangi bir bekletme süresinde, saklama koşulları OGD’leri arasında istatistiksel olarak anlamlı fark yoktu (p>0.05). Altın standart dışındaki diğer bekletme süreleri karşılaştırıldığında, 24 saat bekletme süresi ile diğer bekletme süreleri OGD’leri arasında istatistiksel olarak anlamlı fark vardı (p<0.05). Sonuç: Plakların ışınlama sonrası karanlık ortamda ve karton koruyucu içinde 10 dk.’yı geçmeyen bekletme süresi ile bekletilmesinin OGD’ye etkisi önemsizdi. Sadece plastik bariyerde ve 24 saat sürede bekletilen plakların görüntülerdeki OGD artışı dikkat çekiciydi.

Luminescence characteristics and X-ray-induced defects in BaFBr:Eu2+ storage phosphor.

Three different approaches used to synthesize a sensitive BaFBr:Eu2+ X-ray storage photostimulated luminescence (PSL) phosphor at 850°C for 1 h in a reducing atmosphere are reported. The effects of F/Br and Eu concentration on photoluminescence (PL) and PSL sensitivities synthesized by the three approaches were compared. In the first recipe, BaFBr:Eu2+ prepared using a BaF2 , BaBr2 and EuF3 mixture using solid-state diffusion (Recipe I), even in a reducing atmosphere, yielded a low PL and PSL intensity due to oxygen contamination that acted as competing hole traps. When BaFBr:Eu2+ was prepared using ammonium bromide and ammonium fluoride by two different recipes (Recipes II and III), oxygen contamination was eliminated, resulting in enhanced PSL efficiency. The proposed PSL process in BaFBr:Eu2+ was consistent with the experimental results. Increased F/Br molar ratios would incorporate fluorine ion interstitials that act as hole traps accompanied by bromine ion vacancies that act as electron traps. Although two types of F centres, F(Br- ) and F(F- ) are possible, F(Br- ) centres formed during X-irradiation are only vital for the PSL process. Structural, morphology, and thermoluminescence (TL) properties of the samples were also examined using XRD, field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDAX), and TL studies.

Pressure induced structural phase transitions in calcium halofluorides

Density Functional Theory (DFT) is a powerful tool to investigate the pressure-induced structural phase transitions in materials. We predicted that CaClF and CaBrF undergo a structural transition from P4/nmm to Pnma at 57 GPa and 135 GPa, respectively, while no phase transition is observed for CaIF until the maximum studied pressure of 200 GPa. The electronic structure calculations reveal that the valence band of CaXF are separated into two manifolds due to electronegativity difference between F and X (Cl, Br, I), the manifold close to Fermi level is mainly originated from p-states of X while the well below manifold is derived from the 2p-states of F. The highest electronegativity of F atom makes the difference between alkaline-earth halofluorides and dihalides from their electronic structure, which determines their application as storage phosphors rather than highlight output scintillators similar to alkaline-earth dihalides.

Electron Trapping Optical Storage Using A Single‐Wavelength Light Source for Both Information Write‐In and Read‐Out

AbstractIn conventional electron trapping optical storage phosphor, both short‐ and long‐wavelength light are needed for information write‐in and read‐out, respectively, complicating the optical storage system. Here, a Y3Al2Ga3O12:Pr3+,Eu3+ optical storage phosphor with Pr3+ as an electron donor and Eu3+ as an electron trap is designed, and a single wavelength write‐read scheme is demonstrated, which employs the same blue laser diode (LD) light source for both optical write‐in through two‐photon up‐conversion charging and for read‐out based on photostimulated luminescence (PSL), originated from 4f15d1→4f2 transition of Pr3+ peaked at 315 nm in UV region. A deep electron trap with the mean depth of 1.42 eV and a narrow distribution of 0.3 eV is observed in the presence of Eu3+ in Y3Al2Ga3O12:Pr3+, implying its long‐term storage potential. The write‐in and read‐out experiments are conducted using 450 nm blue LD light with the power density of 1 W cm−2 for write‐in and that with a low power density of 0.02 W cm−2 for read‐out in order to avoid the effect of up‐conversion luminescence on PSL signal. These results will advance the electron trapping optical storage scheme.

Energy-Trapping Management in X-Ray Storage Phosphors for Flexible 3D Imaging.

X-ray imaging has received sustained attention for healthcare diagnostics and nondestructive inspection. To develop photonic materials with tunable photophysical properties in principle accelerates radiation detection technologies. Here the rational design and synthesis of doped halide perovskite CsCdCl3 :Mn2+ , R4+ (R = Ti, Zr, Hf, and Sn) are reported as next generation X-ray storage phosphors, and the capability is greatly improved by trap management via Mn2+ site occupation manipulation and heterovalent substitution. Specially, CsCdCl3 :Mn2+ , Zr4+ displays zero-thermal-quenching (TQ) radioluminescence and anti-TQ X-ray-activated persistent luminescence even up to 448 K, further revealing the charge-carrier compensation and redeployment mechanisms. X-ray imaging with the resolution of 12.5 lp mm-1 is demonstrated, and convenient 3D X-ray imaging for the curved objects is realized in a time-lapse manner. This work demonstrates efficient modulation of energy traps to achieve high storage capacities and promote future research into flexible X-ray detectors.

Mn2+-Activated Photostimulable Persistent Nanophosphors by Pr3+ Codoping for Rewritable Information Storage

Photostimulable luminescence (PSL) nanophosphors, which exhibit superior features including controllable energy storage and efficient photon release upon light stimulation, are desirable for optical signal storage. However, trap tuning of the storage phosphor remains a great challenge. Herein, the PSL of Zn2GeO4:Mn2+ nanophosphors is enhanced via creating deep traps through nonequivalent Pr3+ doping. The possible enhanced mechanisms are analyzed combined with doping models using the first-principles theory. A mechanism is proposed based on changing the coordination environment of Mn2+, creating deep traps and tuning the band gap structure, and thus providing the chance for electrons’ photoionization and PSL generation. As a result, the prepared nanophosphors demonstrate the superior functionalities for optical signal storage. This work not only offers an insight into defect engineering through doping strategies for developing PSL materials but also supplies a good candidate for optical information storage.