Persistent Phosphors Research Articles

Improved synthetic method for the color-tunable LiYGeO4:Tb3+ persistent phosphor toward information storage

Efficient and stable persistent phosphors play a crucial role in the fields of energy storage, anti-counterfeiting, and biomedical fields. Here, we present an improved synthetic method for preparing a series of color-tunable LiYGeO4:Tb3+ persistent phosphor. The increased Tb3+ concentration in the improved method enhances the persistent luminescent intensity at 20 s by ∼ 2.96 times. This enhancement is due to the dual roles of Tb3+ as both emitters and trap centers within LiYGeO4. By simply increasing the doping concentrations, the persistent color can be adjusted from blue to green. LiYGeO4:Tb3+ exhibits no loss of persistent luminescent intensity even after exposure to water at 80 °C for 72 hours, surpassing the commercial green persistent phosphor. Furthermore, information storage was successful demonstrated by using LiYGeO4:Tb3+ with various doping concentrations. This study represents a significant advancement in optimizing the properties of persistent luminescent materials, where dopants simultaneously serve as emitters and trap centers.

Novel non-thermoluminescent CaSO4:Dy dosimeters

The non-thermoluminescence afterglow-based dosimetry performance of self-agglomerating pellet-shaped CaSO4:Dy phosphors synthesized through a low-cost, environmentally friendly method is first reported. Thermoluminescence (TL) and afterglow (AG) were analyzed in samples exposed to beta particle irradiation in the dose range from 0.06 to 8.0 Gy. Characteristic TL glow curves consist of an intense TL maximum at 134 °C, a shoulder at 200 °C, and a maximum at 447 °C. CaSO4:Dy exhibits a highly sensitive AG response for 24 hours with linear behavior from 0.06 Gy to 8.0 Gy. A remarkable reproducibility of both the TL and the AG response was observed in repeated irradiation–readout cycles with no need for pre-irradiation annealing. The synthesized CaSO4:Dy exhibits promising properties to be used as an AG-based dosimeter for real-time radiation detection and dosimetry. Moreover, this phosphor might be applied as a long persistent phosphor (LPP), being a cost-effective alternative to other available LPPs.

Optical Evidence of Charge Trapping at Lanthanide Codopants in SrAl2O4:Eu,Ln (Ln = Nd, Sm, Dy) Persistent Phosphors

AbstractIn this work, the absorption spectra of metastable Dy2+, Nd2+, and Sm2+ are identified in SrAl2O4:Eu,Ln persistent phosphors after excitation with blue light, thereby confirming that the persistent luminescence is indeed due to a charge transfer between the two lanthanide dopants. In contrast to previous studies relying on X‐ray absorption spectroscopy to observe charge transfers between dopants, here low‐energy light is exclusively employed to probe for changes in the absorption spectrum of the phosphor, thereby only minimally affecting the state of the phosphor. Optical bleaching in combination with thermoluminescence measurements allowed to assign which optically active trapping centers contribute to the afterglow of the persistent phosphors.

Quantification of Emission Efficiency in Persistent Luminescent Materials

AbstractAccurate quantification of efficiency enables rigorous comparison between different photoluminescent materials, providing an optimization path critical to the development of next‐generation light sources. Persistent luminescent materials exhibit delayed and long‐lasting luminescence due to the temporary storage of optical energy in engineered structural defects. Standard characterization methods do not provide a universal comparison of phosphor performance, hindering the evaluation of the efficiency of the various processes involved in afterglow. Here, a protocol is established to determine the quantum yield of persistent phosphors by considering the ratio of photons emitted in the afterglow and during charging to those absorbed. The method is first applied to transparent single crystals of the most common persistent phosphors, such as SrAl2O4:Eu2+,Dy3+ and Y3Al2Ga3O12:Ce3+,Cr3+. The versatility of the methodology is demonstrated by quantifying the quantum yield of a ZnGa2O4:Cr3+ thin film, a material widely used in in vivo imaging. The high efficiency of strontium aluminate is confirmed, and a strong dependence of the obtained values on the illumination conditions is revealed, highlighting a trade‐off between efficiency and brightness. The results contribute to the development of standardized protocols for analyzing afterglow mechanisms and assessing overall efficiency, facilitating rigorous comparison and optimization of persistent materials beyond trial‐and‐error approaches.

ZGSO:Cr3+,Ni2+ Persistent Phosphors with Dual Emission in NIR-I and SWIR Ranges for Bio-Imaging Applications.

Persistent luminescence (PersL) is widely used for near infrared (NIR-I, 650-950nm) imaging as they allow getting images without background. Bio-imaging in the second shortwave-infrared region SWIR-II (NIR-II, 1000-1400nm) is less widespread but is growing as it offers the advantages of low photon scattering, increased in vivo penetration depth, and improved imaging clarity. In this work, the preparation and the complete optical properties of a new material is reported, Zn1.33Ga1.33Ni0.005Cr0.005Sn0.33O3.995 (ZGSO:Cr3+, Ni2+) able of emitting in both deep-red/NIR-I and SWIR (NIR-II) and shows its potential in bioimaging. ZGSO:Cr3+, Ni2+ can be excited using different sources such as X-rays, UV, and visible light to emit persistent signals in dual biological windows (dual-BW). By integrating an energy transfer process from Cr3+ to Ni2+ within this newly synthesized material, the influence of co-dopants on signal intensity and emission wavelengths is sought to explore. PersL at ≈700nm (NIR-I) and ≈1300nm (NIR-II) have been tested in preliminary bioimaging experiments using different protocols, allowing signal detection with good spatial resolution and depth sensitivity. The dual-BW PersL imaging strategy expands the toolbox for highly accurate analysis and has, for the first time, allowed access to accurately high-resolution sensing, and tracing.

X-ray/γ-ray/Ultrasound-Activated Persistent Luminescence Phosphors for Deep Tissue Bioimaging and Therapy.

Persistent luminescence phosphors (PLPs) can remain luminescent after excitation ceases and have been widely explored in bioimaging and therapy since 2007. In bioimaging, PLPs can efficiently avoid tissue autofluorescence and light scattering interference by collecting persistent luminescence signals after the end of excitation. Outstanding signal-to-background ratios, high sensitivity, and resolution have been achieved in bioimaging with PLPs. In therapy, PLPs can continuously produce therapeutic molecules such as reactive oxygen species after removing excitation sources, which realizes sustained therapeutic activity after a single dose of light stimulation. However, most PLPs are activated by ultraviolet or visible light, which makes it difficult to reactivate the PLPs in vivo, particularly in deep tissues. In recent years, excitation sources with deep tissue penetration have been explored to activate PLPs, including X-ray, γ-ray, and ultrasound. Researchers found that various inorganic and organic PLPs can be activated by X-ray, γ-ray, and ultrasound, making these PLPs valuable in the imaging and therapy of deep-seated tumors. These X-ray/γ-ray/ultrasound-activated PLPs have not been systematically introduced in previous reviews. In this review, we summarize the recently developed inorganic and organic PLPs that can be activated by X-ray, γ-ray, and ultrasound to produce persistent luminescence. The biomedical applications of these PLPs in deep-tissue bioimaging and therapy are also discussed. This review can provide instructions for the design of PLPs with deep-tissue-renewable persistent luminescence and further promote the applications of PLPs in phototheranostics, noninvasive biosensing devices, and energy harvesting.

Improvement of thermal damage resistance of SrAl2O4:Eu2+, Dy3+ persistent phosphor by a low temperature pre-annealing and its mechanism

SrAl2O4:Eu2+, Dy3+ as an excellent persistent phosphor has been widely applied in many fields. However, the high temperature induced thermal failure has always been a bottleneck problem restricting its long-term development. In this study, a simple pre-annealing method was utilized to improve the thermal damage resistance ability of SrAl2O4:Eu2+, Dy3+ persistent phosphors. After annealing at 900 °C, the afterglow duration time of the phosphor pre-annealed at 400 °C reached 233 min, which was twice longer than that of the phosphor without pre-annealing. An extrinsic vacancy defect migration theory at an elevated temperature was proposed to explain the interesting phenomenon. This study introduced a path to enhance the thermal stability of SrAl2O4:Eu2+, Dy3+ persistent phosphors and provided a thought to design persistent luminescence materials with desired thermal stability.

Optically driven ultraviolet-C glowing from an in situ trapping-detrapping approach.

In recent years, the world has witnessed rapid progress in research on ultraviolet luminescent materials, ranging from high-level anticounterfeiting and solar-blind optical tagging to antibacterial applications. In particular, a background-signal free solar-blind surveillance of ultraviolet-C photons provides an opportunity in bright indoor and outdoor environments. However, ambient daylight or inevitable external photostimulation is always eliminated or underestimated in the research of persistent phosphors. Herein, an in situ trapping-detrapping experimental procedure is employed to reveal more information on the total trap energy and trap modulations after photostimulation. Our findings reveal the presence of optically active trapping defects with photostimulated detrapping and retrapping behavior. This work provides a fundamental advance in revealing the trap distribution and trap reshuffling during glowing-in-the-daylight events, offering what we believe to be new insights into manipulating traps.

Low temperature recombination luminescence of Mg3Y2Ge3O12:Tb3+

A study was conducted to examine the recombination processes in persistent phosphor Mg3Y2Ge3O12:Tb3+ garnet at low temperatures. Photoluminescence (PL), recombination luminescence (RL), electron paramagnetic resonance (EPR), and EPR detected by PL or RL were measured.In samples with low Tb3+ concentration, a broad PL and RL band around 400–450 nm and characteristic Tb3+ lines were observed. However, in samples with high Tb3+ concentration, only Tb3+ lines were present. Both the broad-band and the line components exhibit long-lasting tunneling luminescence with hyperbolic decay. After 263 nm UV irradiation signals of intrinsic electron (F-type) and hole (V-type) trapping centres were observed in the EPR spectra. Such signals were also observed in RL-detected EPR spectra, indicating that the broad RL band at low Tb3+ concentrations originates from tunneling recombination between these intrinsic traps. At high Tb3+ concentrations, the RL-EPR spectrum was not observed, suggesting that intrinsic electron and Tb-related hole trapping centres probably participate in the tunneling recombination.

Simultaneously enhanced photoluminescence and persistent luminescence in SrLaAlO4: Tb type layered perovskite via Gd3+ codoping

Gd3+ co-doping is effective to enhance the photoluminescence of rare earth activators in various host due to energy transfer, however, it is rarely reported via such strategy to regulate persistent luminescence properties. In this work, Gd3+ was co-doped into the SrLaAlO4: Tb persistent luminescence phosphors, and it is found that the photoluminescence and persistent luminescence of the products can be simultaneously improved. The results indicate that as the doping concentration of Gd3+ increases, the particle diameters increase which contributes the increased luminescence. Additionally, an energy transfer process from Gd3+ to Tb3+ ions was observed, which enhances the emission of Tb3+ ions. Furthermore, the persistent luminescence properties of the synthesized phosphors were improved. When the UV light source is turned off, the persistent luminescence of SrLaAlO4: 0.03Tb3+, xGd3+ (x = 0.00–0.97) can last for more than 2 h, which is 100 % enhanced compared to SrLaAlO4: 0.03Tb3+. The trap distribution of SrLaAlO4: 0.03Tb3+, xGd3+ (x = 0.00–0.97) phosphors was analyzed by thermoluminescence. It is found that after the substitution of La3+ with Gd3+, the trap position shifted towards higher temperatures and the trap concentration increased. The initial intensity of the persistent luminescence was also enhanced after Gd3+ co-doping. Based on the experimental findings, the luminescence and persistent luminescence mechanism of SrLaAlO4: 0.03Tb3+, xGd3+ (x = 0.00–0.97) phosphors were described and discussed.

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.

Persistent ultraviolet luminescence and photocatalytic properties of SiO2-Zn2SiO4:Ga,Pb nanoparticles

Persistent phosphors possess unique afterglow optical properties. In this paper, a class of ultra-violet (UV) persistent luminescence nanoparticles were developed for catalytic photodegradation applications. UV persistent luminescence nanoparticles of SiO2-Zn2SiO4:Ga and SiO2-Zn2SiO4:Ga,Pb were successfully synthesized by using a mesoporous template method. The UV persistent luminescence intensity of SiO2-Zn2SiO4:Ga at 405 nm was enhanced up to ca. 3.5 times by co-doping with Pb2+ (396 nm), along with longer persistent luminescence duration. The photodegradation results indicate that it is useful to introduce UV persistent luminescence property into SiO2-Zn2SiO4:Ga,Pb to obtain enhanced catalytic activity of SiO2-Zn2SiO4 with a bigger catalytic oxidation reaction kinetic constant (up to ∼4 times). This kind of UV persistent catalysis strategy may become a potential feasible method for better catalytic photodegradation activity. The UV persistent photocatalyst has potential applications in the photooxidation of organic molecules in high chroma and/or turbidity aqueous systems.

Multiband MgAl0.05Ge0.95O3:0.3%Pr3+ Persistent Phosphor as Efficient Tracers in Crude Oil Emulsions.

The use of fluorescent nanoparticles (NPs) for tracing purposes in oilfields encounters challenges due to background interferences under constant external excitation caused by organic residues present in crude oil. This results in insufficient sensitivity and lower tracer detection limits in the crude oil/water emulsions. In this study, we present the synthesis of persistent luminescent NPs, showcasing their remarkable application as tracers in crude oil. The multiband MgAl0.05Ge0.95O3:0.3%Pr3+ persistent NPs were synthesized via the sol-gel method. Through meticulous experimentation and analysis, our study unveils a novel avenue for efficient and lasting traceability in crude oil. The synthesized NPs emit light across the visible, near-infrared, and shortwave infrared regions, allowing for versatile detection. The unique luminescent properties of these NPs, particularly their ability to persist in emitting light without a continuous external excitation, enable their effective use as tracers in crude oil/water emulsions where background fluorescence typically poses a significant challenge. By employing these persistent NPs in background fluorescence-free conditions, we achieve ultrahigh sensitivity in detecting these NPs in crude oil. Our research reveals that the doping of Al3+ ions significantly enhances both the afterglow intensity of MgGeO3:0.3%Pr3+ phosphor and the afterglow decay time of Pr3+ emission. This characteristic enables the re-excitation of MgAl0.05G0.95O:0.3%Pr3+ NPs within the emulsion, allowing for repeated spectral and imaging acquisition. This high sensitivity not only facilitates precise imaging of NPs in crude oil but also enables long-term monitoring in real-time, offering valuable insights for oilfield operations.

Red-to-ultraviolet light chargeable Sm2+-activated deep-red persistent phosphor for simultaneous bioimaging and bio-temperature sensing

Persistent phosphor-based bio-applications do not need real-time photo-excitation and do not suffer from disturbance of stray excitation light, auto-fluorescence of the measured substance and heat produced by excitation. However, the persistent phosphors that well match the optical biological windows are deficient. Here, we report for the first-time divalent samarium (Sm2+) activated persistent phosphor with dual-functionality for simultaneous bioimaging and bio-temperature sensing. The persistent phosphor is Sm2+ and Nd3+codoped SrAl2Si2O8 that can be photo-charged in 250–660 nm and shows deep-red persistent luminescence (PersL) originated from both the 4f55d1 → 4f6 and 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions that well match the first optical biological window. The intense PersL output shows the effective operation temperature range of 240–340 K, covering the physiological temperature range of 298–325 K. It is found that quantum tunneling dominates both the visible light including red light charging process and PersL generating process. The temperature dependent PersL intensity ratio of the thermally coupled 4f55d1 → 4f6 emission band and the 5D0 → 7FJ emission lines is studied and a maximum relative sensitivity of 4.81 % K−1 at 200 K and 2.17–1.82 % K−1 in the physiological temperature range are achieved. The dual-functionality of SrAl2Si2O8:1 %Sm2+,1 %Nd3+ for simultaneous bioimaging and bio-temperature sensing is demonstrated. Our findings open up new scenarios for multifunctional applications of Sm2+.

Modulating Heavy Atom Effect in Germylene for Persistent Room Temperature Phosphorescence.

It is worth but still challenging to develop the low-valent main group compounds with persistent room temperature phosphorescence (pRTP). Herein, we presented germylene-based persistent phosphors by introduction of low-valent Ge center into chromophore. A novel phosphors CzGe and its series of derivatives, namely CzGeS, CzGeSe, CzGeAu, and CzGeCu, were synthesized. Experiments and theoretical calculations reveal that the pRTP behavior were "turn on" due to the heavy atom effect of germylene. More importantly, the low-valent of oxidation state and structural traits propelled GeCz had a balance between the intersystem crossing and the shortening of lifetime caused by the heavy atoms, resulting the ultralong lifetime of 309 ms and phosphorescent quantum efficiency of 15.84 %, which is remarkable among heavy main group phosphors. This research provides valuable insights to the design of heavy atoms in phosphors and expand the applications of germylene chemistry.

Tailoring traps in Eu2+ activated persistent phosphors for multilevel information storage and encryption

Persistent luminescence (PersL) phosphors, identified as ideal candidates, hold immense promise for information storage and encryption. However, practical storage and encryption technology using these phosphors remains uncommon due to their weak luminescence intensity and the inconvenience of light sources used in encryption and decryption processes. Here, we have developed Sr2MgSiGeO7:Eu2+,Mn2+,Dy3+ phosphor with a super-long PersL beyond 100 h, the higher charge storage capacity and PersL efficiency (17 %) than commercial SrAl2O4:Eu,Dy phosphors by introduction of co-dopant Mn2+. This phosphor exhibits rapid and efficient charging capability when exposed to various light sources such as sunlight, light-emitting diode, mobile phone and computer screen. To explain the high charge storage capacity and super-long PersL, we propose a novel trap mechanism based on hole-electron defect pair trap structures. Notably, this phosphor as an anti-counterfeiting material demonstrates high-order encryption by the adding specific information writing process via temperature management. This study provides a new paradigm for future design of PersL phosphors and luminescent anti-counterfeiting.

Orange Emitting SrS: Eu2+, Dy3+ Afterglow Phosphor: Structural and Luminescence Properties

SrS:Eu is known as an attractive material for imaging, scintillator, or persistent phosphor applications, thanks to its effective photoluminescence (PL) and thermoluminescence (TL) capabilities, but there are still great mysteries of persistent phosphors and attract great interest. Hence, this work investigated the luminescence properties of well-known persistent phosphor based on SrS using various spectroscopic techniques for detailed characterization. Measurements using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were used to analyze the phase and elements of the phosphor. Belongs to the XRD data the microcrystalline phosphor is cubic, and the diameters ranged from 1 to 100 µm. The morphology of the phosphor was examined by scanning electron microscope (SEM). A time-resolved PL system recorded PL properties, namely the emission and excitation spectra of the phosphor. SrS emits around 626 nm with a broad excitation band peaking around 466 nm. A TLD reader system measured the TL glow curve of the phosphors after UVB radiation. The TL glow curve exhibited a broad peak around 160oC. The dose-response of this peak was obtained up to 600 seconds of exposure to UVB radiation, and it was observed that the dose-response curve exhibits a saturating exponential behavior.

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.

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.

Multi-color and multi-mode luminescence tuning in persistent phosphors by trap engineering

Conventional persistent luminescent phosphors face a significant challenge in developing a single material for multi-color anti-counterfeiting. In this study, a wide range of Cr3+ activated gallium germanate-based persistent phosphors are successfully synthesized using high-temperature solid phase approach. By incorporating Cr3+ and Er3+ as dual emitting centers, and utilizing Yb3+ as a sensitizer and electron traps, the resulting phosphors exhibit an exceptional combination of photoluminescence, up-conversion luminescence, persistent luminescence, photo/thermo-stimulated luminescence, followed by photo-stimulated persistent luminescence in a single material system. Beyond its multi-mode emissions, the luminescence color output can be conveniently controlled by adjusting annealing time, Yb3+ ion doping concentration, excitation wavelength, or excitation power. A systematic study of trap distribution related to PersL has been conducted by regulating annealing temperature, time, doping concentration and type. The responding multi-mode luminescent mechanisms are also proposed. Particularly, these phosphors demonstrated outstanding performance as security labels in advanced anti-counterfeiting applications. This research holds the potential to inspire the design and development of more intricate luminescence anti-counterfeiting materials and technologies.