Persistent Luminescence Research Articles

Cation Occupation Engineering Realizes Valence Modulation of Manganese-Activated ZnGa2O4.

Herein, a series of Mn-activated ZnGa2O4 (ZGO) phosphors have been developed for multifunctional applications. The characteristic green and red emission at 503 and 668 nm of Mn-activated ZGO phosphors can be observed under excitation of 247 and 375 nm, respectively, attributed to the partial oxidation of Mn2+ ions resulting in the coexistence of Mn2+ and Mn4+ ions in the host lattice. The valence modulation of Mn content not only realizes the adjustment of red and green luminescence intensity but also achieves the management of persistent luminescence time and thermo-luminescence time. Further, the codoping of Mg2+ could transform the position occupancy preference of Mn and effectively facilitate the conversion of Mn2+ to Mn4+, leading to the regulation of the valence state of manganese ions. Surprisingly, the existence of Mg2+ ions broadens the emission band of Mn4+ and enhances the photoluminescence intensity to 3.8 times, which can be ascribed to the weakened crystal field leading to the downward shift of the 4T2 energy level and the increase of Mn4+ concentration. For this valence modulation behavior, two different hypotheses about the occupancy of Mg2+ have been proposed to explain the corresponding phenomenon. Finally, the potential applications of the synthesized phosphors have been explored in advanced anticounterfeiting strategies, information storage, and plant lighting field.

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.

Full-color, time-valve controllable and Janus-type long-persistent luminescence from all-inorganic halide perovskites

Long persistent luminescence (LPL) has gained considerable attention for the applications in decoration, emergency signage, information encryption and biomedicine. However, recently developed LPL materials – encompassing inorganics, organics and inorganic-organic hybrids – often display monochromatic afterglow with limited functionality. Furthermore, triplet exciton-based phosphors are prone to thermal quenching, significantly restricting their high emission efficiency. Here, we show a straightforward wet-chemistry approach for fabricating multimode LPL materials by introducing both anion (Br−) and cation (Sn2+) doping into hexagonal CsCdCl3 all-inorganic perovskites. This process involves establishing new trapping centers from [CdCl6-nBrn]4− and/or [Sn2-nCdnCl9]5− linker units, disrupting the local symmetry in the host framework. These halide perovskites demonstrate afterglow duration time ( > 2,000 s), nearly full-color coverage, high photoluminescence quantum yield ( ~ 84.47%), and the anti-thermal quenching temperature up to 377 K. Particularly, CsCdCl3:x%Br display temperature-dependent LPL and time-valve controllable time-dependent luminescence, while CsCdCl3:x%Sn exhibit forward and reverse excitation-dependent Janus-type luminescence. Combining both experimental and computational studies, this finding not only introduces a local-symmetry breaking strategy for simultaneously enhancing afterglow lifetime and efficiency, but also provides new insights into the multimode LPL materials with dynamic tunability for applications in luminescence, photonics, high-security anti-counterfeiting and information storage.

Multi-Mode Luminescence in Smart Near-Infrared Cr3+/Pr3+ Codoped SrGa12O19 Phosphors Induced by Three Distinct Excitation Mechanisms.

Near-infrared (NIR) phosphors have emerged as novel luminescent materials across various fields due to their unique advantages of high penetration and invisibility. However, there is currently a lack of intelligent NIR phosphors that can achieve multimode stimuli responsive for sensing applications. In this study, we employed a high-temperature solid-phase reaction to incorporate Pr3+ into Cr3+-doped gallate magnetite SrGa12O19 phosphor, yielding a multimode luminescent intelligent NIR phosphor. Also, due to the inherent cation vacancies and defects in the matrix, the material not only exhibits brighter photoluminescence but also exhibits distinct NIR mechanoluminescence at a lower load. Notably, Pr3+-doped SrGa12O19:Cr3+ also demonstrates extended persistent luminescence and thermoluminescence effects. Finally, we combined the phosphor with the blue LED chip to develop a new multifunctional NIR pc-LED. Leveraging NIR's unique penetrating ability, it can persist in biological tissues for prolonged periods, enabling optical inspection and offering a novel approach to password protection for anticounterfeiting measures. This intelligent NIR phosphor solution significantly expands the application potential of NIR light in food quality assessment and analysis.

Persistent Luminescence Nanoplatform for Autofluorescence-Free Tracking of Submicrometer Plastic Particles in Plant.

The uptake of plastic particles by plants and their transport through the food chain make great risks to biota and human health. Therefore, it is important to trace plastic particles in the plant. Traditional fluorescence imaging in plants usually suffers significant autofluorescence background. Here, we report a persistent luminescence nanoplatform for autofluorescence-free imaging and quantitation of submicrometer plastic particles in plant. The nanoplatform was fabricated by doping persistent luminescence nanoparticles (PLNPs) onto polystyrene (PS) nanoparticles. Cr3+-doped zinc gallate PLNP was employed as the dopant for autofluorescence-free imaging due to its persistent luminescence nature. In addition, the Ga element in PLNP was used as a proxy to quantify the PS in the plant by inductively coupled plasma mass spectrometry (ICP-MS). Thus, the developed nanoplatform allows not only dual-mode autofluorescence-free imaging (persistent luminescence and laser-ablation ICP-MS) but also ICP-MS quantitation for tracking PS in plant. Application of this nanoplatform in a typical plant model Arabidopsis thaliana revealed that PS mainly distributed in the root (>99.45%) and translocated very limited (<0.55%) to the shoot. The developed nanoplatform has great potential for quantitative tracing of submicrometer plastic particles to investigate the environmental process and impact of plastic particles.

Nonstoichiometry-Induced Self-Activated Phosphors for Dynamic Anti-counterfeiting Applications.

Optical signals with distinctive properties, such as contactless, fast response, and high identification, are harnessed to realize advanced anti-counterfeiting. However, the simultaneous attainment of multi-color, -temporal, and -modal luminescence performance remains a compelling and imperative pursuit. In our work, a temperature/photon-responded dynamic self-activated luminescence originating from nonstoichiometric Zn2GeO4 is developed with the modulation of intrinsic defects. The increased concentration of oxygen vacancies (VO••) contributes to an enhanced recombination of ZnGe″-VO••, ultimately improving the self-activated luminescence performance. Additionally, the photoluminescence (PL) color of the representative Zn2.2GeO4 sample changes from green to blue-white with the increased ultraviolet (UV) irradiation time. Concurrently, the emission color undergoes a variation from blue to green as the ambient temperature raises from 280 to 420 K. Remarkably, green long persistent luminescence (LPL) and photostimulated luminescence (PSL) behaviors are observed. Herein, this study elucidates a sophisticated anti-counterfeiting approach grounded in the dynamic luminescent attributes of nonstoichiometric Zn2GeO4, presenting a promising frontier for the evolution of anti-counterfeiting technologies.

Amorphous to Crystalline Phase Transformation Enables Tunable Persistent Luminescence for Multi‐Mode Optical Information Storage

AbstractMulti‐mode luminescence tuning through in situ crystallization of topological glass holds significance for photonics applications. Here, NaAlSiO4:Eu2+‐based glass ceramics are presented as stable persistent luminescence (PersL) materials by controlling the phase transformation in Eu2+ doped Na2O‐Al2O3‐SiO2 from amorphous glass to crystalline nepheline phase. X‐ray and UV excited PersL colors from blue to yellow are realized by adjusting the crystallization duration time, and trap statuses reveal the dynamic PersL process with a trap redeployment from 0.83 to 1.09 eV during the transformation. Optical information storage model is constructed with a structure of stacked emitting layers to enhance storage capacity. X‐ray excited luminescence time‐lapse imaging is further demonstrated with optical memory longer than 5 days. These findings advance the development of superior stable PersL glass ceramics and offer optical manipulation tactics for multi‐mode optical information storage applications.

Stepwise Charge/Energy Transfer in MR-TADF Molecule-Doped Exciplex for Ultralong Persistent Luminescence Activated with Visible Light.

Organic long-persistent luminescence (OLPL), which relies on energy storage for delayed light emission by the charge separation state, has attracted intense attention in various optical applications. However, charge separation (CS) is efficient only under ultraviolet excitation in most OLPL systems because it requires a driving force from the large energy difference between the local excited (LE) and charge transfer (CT) states. In this study, a multiresonance thermally activated delayed fluorescence (MR-TADF) molecule is incorporated into an exciplex system to achieve efficient OLPL in a composite material activated by visible light via a stepwise charge/energy transfer process. The enhanced absorption of the composite material facilitated a tenfold increase in the duration of the OLPL, which can last for several hours under visible light excitation. The excited state of the MR-TADF molecule tends to charge transfer to the acceptor, followed by energy transfer to the exciplex, which benefits from the small difference between the LE and CT states owing to the inherent CS characteristics of the opposing resonance effect. Afterglow displays of these composite materials are fabricated to demonstrate their considerable potential in encryption patterns and emergency lights, which take advantage of their excellent processability, visible light activation, and tunable luminescence properties.

Mechanism and dynamic analysis of persistent luminescence in phosphors Sr2MgSi2O7: Eu2+, Dy3+

The persistent luminescent (PSL) phosphors Sr2-x-yMgSi2O7: xEu2+, yDy3+ (x = 0∼0.08, y = 0∼0.08) were synthesized by a solid-state reaction method in a weak reductive atmosphere of 5%-H2/N2. Comprehensive measurements were carried out to study the effects of Eu2+ and Dy3+ doping amount on the crystal phase, photoluminescence (PL), afterglow decay properties, and trap energy levels. The results indicated that the impurity phases decreased and disappeared, and crystalline grains tended to be larger and denser with the doping amount of Eu2+ and Dy3+ increasing. We shed light on the origination of asymmetric PL peak, concentration quenching of Eu2+ ions, time evolution of PSL specture and chromaticity of Eu2+, Dy3+ co-doped phosphors. Based on the deconvolutions of X-ray photoelectron spectroscopy (XPS) spectra and thermoluminescence (TL) spectra, the types and energy depth of traps in these phosphors were systematically studied. According to the data of PL, PLE, and TL, we deduced a schematic diagram of the energy level and discussed the mechanism of PSL of the phosphors. As Dy3+ dopant increases, the Eu2+, Dy3+ co-doped phosphors not only generate more defects of VO•• and VSrʺ, but also introduce DySr• defect with proper trap depth, meanwhile, a thermally assisted tunneling mechanism will gradually dominate during the persistent luminescence, which is responsible for that the phosphor with x = 0.02, y = 0.01 presents the best long afterglow property.

Enabling Visible-Light-Charged Near-Infrared Persistent Luminescence in Organics by Intermolecular Charge Transfer.

Visible light is a universal and user-friendly excitation source; however, its use to generate persistent luminescence (PersL) in materials remains a huge challenge. Herein, the concept of intermolecular charge transfer (xCT) is applied in typical host-guest molecular systems, which allows for a much lower energy requirement for charge separation, thus enabling efficient charging of near-infrared (NIR) PersL in organics by visible light (425-700nm). Importantly, NIR PersL in organics occurs via the trapping of electrons from charge-transfer aggregates (CTAs) into constructed trap states with trap depths of 0.63-1.17eV, followed by the detrapping of these electrons by thermal stimulation, resulting in a unique light-storage effect and long-lasting emission up to 4.6 h at room temperature. The xCT absorption range is modulated by changing the electron-donating ability of a series of acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile-based CTAs, and the organic PersL is tuned from 681 to 722nm. This study on xCT interaction-induced NIR PersL in organic materials provides a major step forward in understanding the underlying luminescence mechanism of organic semiconductors and these findings are expected to promote their applications in optoelectronics, energy storage, and medical diagnosis.

Differential response under X-ray/UV dual-mode excitation in single-component defect state phosphor X-ray imaging and Wavelength-Multiplexing information storage

Multimodal Excitation Response (MMER) phosphors are gaining rapid attention due to their outstanding performance and emerging applications. Herein, a Eu2+, Mn2+ co-doping CaAl2Si2O8 phosphor is reported. Unlike common MMER phosphors, this system exhibits blue photo-/persistent luminescence under 365 nm UV excitation, orange photo-/persistent luminescence under X-ray excitation, and X-ray-induced photochromism. These diverse optical properties enable it to exhibit advanced bright/dark dual-field X-ray imaging and wavelength-multiplexing information storage. Furthermore, the testing results indicate that the varying color response to UV and X-ray excitation benefits from different excitation properties between Eu2+ and Mn2+ as well as precise emitter/trap local units. Thus, this work not only provides an excellent candidate for versatile applications but also offers a design approach for such materials.

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.

Dynamic optical information encryption strategy based on rare earth ions doped BaSi2O5 phosphors with adjustable trap distribution

Multi-modal strategies for optical information storage have received a lot of attention to meet the increasing security requirements. In this case, long persistent luminescence (LPL) phosphors with different dopant ions were obtained by introducing Dy3+ and Ho3+ ions into the BaSi2O5:Eu2+ phosphor to adjust the distribution and depth of the trap centers. The generation of the pure phase BaSi2O5 was confirmed by X-ray diffraction (XRD) and XRD Rietveld refinement. The peak emission of BaSi2O5: Eu2+ phosphor is about 500 nm with 313 nm excitation. Both BaSi2O5: Eu2+, Dy3+, and BaSi2O5: Eu2+, Ho3+ phosphors exhibit emission characteristics of Eu2+ ions. The trap depths of the three phosphors are different by Gaussian fitting of thermoluminescence (TL) curves, and the depth of BaSi2O5: Eu2+, Dy3+ phosphor can reach 1.070 eV. Typically, the flexible luminescent film based on BaSi2O5: Eu2+ phosphor can be written optical pattern using 365 nm ultraviolet (UV) light, such as "DL" and "fireworks" patterns, and subsequently read out by thermal or infrared light stimulus. Further, a strategy for encryption and decryption of dynamic optical information in Morse code has been developed using BaSi2O5: Eu2+, BaSi2O5: Eu2+, Dy3+, and BaSi2O5: Eu2+, Ho3+ phosphors, indicating the prospective use in optical information security.

Persistent Luminescence Nanosensors: A Generalized Optode-Based Platform for Autofluorescence-Free Sensing in Biological Systems.

Fluorescent nanosensors have revolutionized diagnostics and our ability to monitor cellular dynamics. Yet, distinguishing sensor signals from autofluorescence remains a challenge. Here, we merged optode-based sensing with near-infrared-emitting ZnGa2O4:Cr3+ persistent luminescence nanoparticles (PLNPs) to create nanocomposites for autofluorescence-free "glow-in-the-dark" sensing. Hydrophobic modification and incorporation of the persistent luminescence nanoparticles into an optode-based nanoparticle core yielded persistent luminescence nanosensors (PLNs) for five analytes (K+, Na+, Ca2+, pH, and O2) via two distinct mechanisms. We demonstrated the viability of the PLNs by quantifying K+ in fetal bovine serum, calibrating the pH PLNs in the same, and ratiometrically monitoring O2 metabolism in cultures of Saccharomyces cerevisiae, all the while overcoming their respective autofluorescence signatures. This highly modular platform allows for facile tuning of the sensing functionality, optical properties, and surface chemistry and promises high signal-to-noise ratios in complex optical environments.

Relationship between photochromism and persistent luminescence in barium-magnesium silicates

Photochromism and persistent luminescence (PersL) are two fascinating light-responsive effects in phosphors, both of which have found widespread applications in optical switching, optical anticounterfeiting and information storage. However, the relationship between photochromism and PersL has not been clarified, thus greatly limiting the use and design of the light-responsive materials in multifunctional applications. Herein, taking BaMgSiO4:Eu2+, TM (TM = transition metal: Fe, Co and Cr) as model materials, we first reveal that photochromism and PersL could be two independent photophysical effects, although they are both related to the charge carrier trapping/detrapping processes. Notably, photochromism and PersL show have different responses to light wavelengths, and the depth of traps involved in the two effects is also quite different. Moreover, by codoping different transition metal elements, we obtain the largest reflectance difference of ∼71 % among inorganic photochromic materials reported thus far, and demonstrate interesting multicolor photochromism, including magenta, golden and pink. Based on their distinct response to light and temperature, a multi-functionalized optical anticounterfeiting technology is proposed, which may open up a new avenue for applying the light-responsive materials in flexible electronics and wearable devices.

Growth, structure and optical characterization of new Pr3+-doped LaGaGe2O7 and LaGa0.6Al0.4Ge2O7 single crystals

In this work, a new crystal belonging to the germanate family: LaGaGe2O7 (or LGGO) doped with trivalent Praseodymium (Pr) ion is studied. We report the first single crystal growth of this material using the Czochralski method. The spectroscopic properties including absorption and emission cross-sections of praseodymium in this new matrix are measured, as well as the refractive index along the dielectric axes. This material exhibits very high emission cross sections of 38, 20, and 16 10−20 cm2 at 746 nm, 646 nm and 620 nm, respectively. Some persistent luminescence is observed in Pr:LGGO after UV irradiation at 254 nm. To reduce the phenomenon, the solid solution LaGa1-xAlxGe2O7 (0 ≤ x ≤ 1) is considered. Thermoluminescence experiments show that a substitution of 40 % of gallium by aluminium in the crystal structure allows to suppress this persistent luminescence phenomenon.

LiGa5O8: Fe3+: A novel and super long near-infrared persistent material

The development of near-infrared persistent materials has become a popular research area owing to their diverse applications. However, the efficient emitters for these materials remains limited. Cr3+ is one of the strongest candidates, since it displays better performance with long duration. Fe3+ is a potential nontoxic alternative although its performance is not as good as Cr3+. In this study, a series of novel Fe3+-activated near-infrared long afterglow phosphors of LiGa5O8 have been prepared. Photoluminescence and persistence luminescence spectroscopy have been collected to investigate its optical properties. Furthermore, the trap characteristics of the samples were systematically analyzed by collecting thermoluminescence signals. The results indicate that there is an intense near-infrared emission centered at 675 nm and a long afterglow duration of more than 28 h for the optimized sample. Trap analysis indicates that oxygen vacancy defects are not the primary reasons for the extraordinarily long afterglow in these samples. Instead, the interaction of other trap types, such as antisite defects, probably contribute to the excellent afterglow properties of the material.

Multicolor tunable persistent luminescence mechanism in well-designed inorganic composites.

Herein, by ball milling CsPb(Br/I)3 quantum dot glass powder with Sr2MgSi2O7:Eu2+, Dy3+ phosphor, multicolor tunable long persistent luminescence (LPL) in inorganic composites with more than 700 min attenuation time can be obtained via a radiation photon reabsorption process. Attractively, the wide color gamut of LPL spectra overlaps the National Television System Committee space 74%. Notably, the luminescence intensity remains stable when the inorganic composites are composed with UV light for 100 h. Finally, practical anticounterfeiting application is successfully realized based on the prepared LPL inorganic composites. This work provides a new, to the best of our knowledge, perspective to achieve polychromatic adjustment of LPL.

Improvement of Hydrogen Peroxide and Glucose Detection in Serum using Persistent Luminescent Nanoparticles: Impact of Synthesis Parameters and Particle Size

AbstractPersistent Luminescent Nanoparticles (PLNPs) emit prolonged light after excitation, allowing getting images with high signal‐to‐noise ratio, making them particularly beneficial for in vitro biodetection. In this study, we report the preparation of a library of gallium and zinc‐based Persistent Luminescent Nanoparticles doped with chromium (ZnGa2O4:Cr3+) through two distinct syntheses conducted at 120 °C for 12 hours or 24 hours, followed by a calcination at 500 °C or 750 °C. Using centrifugation, and starting from polydisperse samples, we demonstrated the ability to achieve different sizes in a monodisperse manner. Furthermore, our research revealed that ZnGa2O4:Cr3+ (ZGO) nanoparticles react differently with hydrogen peroxide (H2O2) based on their size, synthesis duration, and calcination temperature. We observed the most significant amplification of persistent luminescence for ZGO particles prepared at 120 °C for 12 hours and calcinated at 500 °C, with a size of approximately 100 nm, in the presence of 100 mM H2O2 (later named ZGO‐2). This study enabled the detection of H2O2 in serum without autofluorescence using the developed PLNPs, with a detection limit of up to 2.1 μM and a recovery rate of around 99 %. Additionally, we designed a glucose test for based on the responsiveness of ZGO PLNPs to H2O2. Using glucose oxidase, the glucose detection limit in serum was established around 0.13 μM, with a detection range between 0–5 μM. These findings could open new avenues to further control the size, synthesis, calcination temperature, and persistent luminescence of PLNPs, thus enhancing their utility in the development of new in vitro biosensors.

Biological window excited up-conversion persistent luminescence nanoparticles for bioimaging and photodynamic therapy

Near-infrared (NIR) persistent luminescence nanoparticles (PLNPs) have inherent advantages for high-sensitivity bioimaging due to the separation of excitation and emission light. However, the single-wavelength emission of NIR PLNPs for bioimaging limits their use in photodynamic therapy (PDT). Herein, a biological window excited up-conversion (UC) PLNPs, Zn3Ga2SnO8:Cr3+,Yb3+,Ho3+ (ZGS), was reported for bioimaging and PDT. ZGS exhibits NIR persistent luminescence (PersL) after red LED excitation and visible UCL under 980 nm excitation. The NIR PersL is designed for in vivo bioimaging; the visible UCL is used to activate photosensitizer (PS) to generate reactive oxygen species (ROS) for PDT. The dual-functional ZGS with UCL and PersL provides an effective method for bioimaging and PDT, which is expected to further promote the application of PLNPs in the integration of efficient diagnosis and treatment.