Persistent Luminescence Materials Research Articles

Development of a red persistent luminescent composite: Electrospun nanofiber polymer coating prevents emission quenching by water

Sulfide persistent luminescent materials are known for their efficient luminescence, although a limitation in application of these materials is their susceptibility to hydrolysis. In this work, the electrospinning technique was used to encapsulate polycrystalline SrS:Eu2+,Sm3+ within PVDF-co-HFP nanofibers, after which thermostimulated luminescence could be observed with the naked eye following treatment with boiling water, confirming that the storage capacity of the powder was maintained after encapsulation. The composite material presented high levels of flexibility, hydrophobicity, and thermal and chemical stability. The structural characteristics of the synthesized SrS:Eu2+,Sm3+ were elucidated using X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The morphologies of the SrS:Eu2+,Sm3+ grains and the electrospun nanofibers were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray fluorescence (XRF) mapping, and scanning transmission X-ray microscopy (STXM). Mechanical properties including elastic modulus and deformation degree were evaluated by PeakForce quantitative nanomechanical mapping (PF-QNM). The luminescent properties were investigated using photoluminescence spectroscopy (PLS), diffuse reflectance spectroscopy (DRS), and X-ray excited optical luminescence (XEOL), which showed that the photonic functionality of the material in the nanofibers was preserved, even after severe treatment with boiling water.

Dehydration-Triggered Afterglow Transition in a Mellitate-Based Coordination Polymer

Stimulus-responsive long persistent luminescence (LPL) materials have attracted wide attention due to their potential applications in information storage, anti-counterfeiting, optoelectronic devices, etc. However, LPL coordination polymers with room temperature afterglow transition characteristics have not been explored. Herein, mellitic acid and zinc ions were utilized to synthesize an acid–base stable coordination polymer (1) by an organic solvent-free hydrothermal method. 1 possesses a tightly stacked structure and exhibits dual-emission peaks with blue luminescence and blue-green afterglow. Upon exposure to heating, DMSO immersion, or vacuum, 1h, 1s, and 1v were obtained. The original blue luminescence changes to blue-green, while the afterglow turns yellow-green due to the loss of water molecules from the inner cavity. This is the first example of an LPL coordination polymer that can realize room temperature afterglow transition by dehydration operation. Moreover, the emission spectra of 1 can be recovered by exposing 1h, 1s, or 1v to water vapor, suggesting a reversible dehydration/hydration process. Experimental and density functional theory (DFT) results suggest that the fluorescence of 1 originates from the mixing of intra-ligand and ligand-to-metal charge transfer excited states. The triplet state from intersystem crossing is responsible for the long persistent luminescence of phosphorescence emission. The rational structural design along with the conceptual model of anti-counterfeiting and information encryption based on afterglow transition display the unique advantages of the LPL coordination polymer in realizing convenient multiple stimuli-responsive devices.

X-ray-activated Bi3+/Pr3+ co-doped LiYGeO4 phosphor with UV and NIR dual-emissive persistent luminescence

X-ray-activated luminescence materials have broad application prospects in photodynamic therapy of deep tissue. Among them, X-ray-activated persistent luminescence materials (PLMs) exhibiting multiple emission peaks have drawn extensive attention for their capacity to achieve a combination of bioimaging and therapeutic functions. Here, we developed a novel PLM, LiYGeO4:Bi3+,Pr3+, that simultaneously exhibits UV and NIR dual persistent luminescence (PersL) emissions after irradiation by X-ray. The material can be repeatedly excited by X-ray and emits similar luminescence intensity every time, which shows good PersL stability. In addition, LiYGeO4:Bi3+,Pr3+ exhibits photostimulated PersL properties by stimulation with a red light-emitting diode (LED) or NIR laser after long-term decay. This work provides a new choice of X-ray-excited PLMs with UV and NIR dual emission and the novel phosphor shows promise as a potential candidate for the integration of treatment and diagnosis of deep tumors.

Highly transparent Ce3+,Cr3+ co-doped GYAGG single crystals with enhanced persistent luminescence

Despite significant interest in persistent luminescence materials, the focus of all recent works remains on the exploitation of materials in powder form. Here, a new point of view based on persistent luminescence in single crystals is presented. The garnet crystals [(Gd0.67Y0.33)3-xCex)](Al2-yCry)Ga3O12 and [(Gd0.33Y0.67)3-xCex](Al2-yCry)Ga3O12 (GYAGG) codoped with Ce3+ and different concentrations of Cr3+ have been elaborated and their persistent luminescence properties are fully characterized within this work. The persistent luminescence of Ce3+, Cr3+-codoped GYAGG single crystals is optimized due to their high optical quality, very good crystallinity and a volume effect where the whole material can be excited and charged by the excitation light. Furthermore, thanks to their transparency, robustness and homogeneity; in-depth optical spectroscopy characterization is possible, shedding light on the mechanism responsible for the afterglow.

High-Efficiency and Stable Long-Persistent Luminescence from Undoped Cesium Cadmium Chlorine Crystals Induced by Intrinsic Point Defects.

Application of long-persistent luminescence (LPL) materials in many technological fields is in the spotlight. However, the exploration of undoped persistent luminescent materials with high emission efficiency, robust stability, and long persistent duration remains challenging. Here, inorganic cesium cadmium chlorine (CsCdCl3 ) is developed, featuring remarkable LPL characteristics at room temperature, which is synthesized by a facile hydrothermal method. Excited by ultraviolet light, the CsCdCl3 crystals exhibit an intense yellow emission with a large photoluminescence quantum yield of ≈90%. Different from the reported systems with lanthanides or transition metals doping, the CsCdCl3 crystals without dopants perform yellow LPL with a long duration of 6000 s. Joint experiment-theory characterizations reveal the intrinsic point defects of CsCdCl3 act as the trap centers of excited electrons and the carrier de-trapping process from such trap sites to localized emission centers contributes to the LPL. Encouraged by the attractive fluorescence and persistent luminescence as well as good stability of CsCdCl3 against environment oxygen/moisture (75%), heat (100°C for 10h), and ultraviolet light irradiation, an effective dual-mode information storage-reading application is demonstrated. The results open up a new frontier for exploring LPL materials without dopants and provide an opportunity for advanced information storage compatible for practical applications.

Thermally Activated Long Persistent Luminescence of Organic Inorganic Metal Halides

AbstractLong persistent luminescence (LPL) materials of SrAl2O4 doped with Eu2+ or Dy3+ can maintain emission over hours after ceasing the excitation but suffer from insolubility, high cost, and harsh preparation. Recently, organic LPL of guest‐host exciplex systems has been demonstrated via an intermediate charge‐separated state with flexible design but poor air‐stability. Here, we synthesized a nontoxic two‐dimensional organic–inorganic metal hybrid halides (OIMHs), called PBA2[ZnX4] with X=Br or Cl and PBA=4‐phenylbenzylamine. These materials exhibit stable LPL emission over minutes at room‐temperature, which is two orders of magnitude longer than those of previously reported OIMHs. The mechanism study shows that the LPL emission comes from thermally activated charge separation state rather than room‐temperature phosphorescence. Moreover, the LPL of PBA2[ZnX4] can be excited by low power sources, representing an effective strategy for developing low‐cost and high‐stability LPL systems.

Thermally Activated Long Persistent Luminescence of Organic Inorganic Metal Halides.

Long persistent luminescence (LPL) materials of SrAl2 O4 doped with Eu2+ or Dy3+ can maintain emission over hours after ceasing the excitation but suffer from insolubility, high cost, and harsh preparation. Recently, organic LPL of guest-host exciplex systems has been demonstrated via an intermediate charge-separated state with flexible design but poor air-stability. Here, we synthesized a nontoxic two-dimensional organic-inorganic metal hybrid halides (OIMHs), called PBA2 [ZnX4 ] with X=Br or Cl and PBA=4-phenylbenzylamine. These materials exhibit stable LPL emission over minutes at room-temperature, which is two orders of magnitude longer than those of previously reported OIMHs. The mechanism study shows that the LPL emission comes from thermally activated charge separation state rather than room-temperature phosphorescence. Moreover, the LPL of PBA2 [ZnX4 ] can be excited by low power sources, representing an effective strategy for developing low-cost and high-stability LPL systems.

Recyclable Time–Temperature Indicator Enabled by Light Storage in Particles

AbstractTime–temperature indicator (TTI) technologies allow for nondestructive and real‐time quality management of perishable products during the entire transport–storage process, which provides an important guarantee for the product safety of end users. However, the existing TTI technologies still have shortcomings in recyclability, sensitivity, and environmental tolerance, limiting their widespread applications. Herein, a new TTI route based on the light storage effect in persistent luminescent (PersL) materials is proposed. Such TTI is designed on account of the principle that the release rate of light‐induced trapped carriers in PersL materials is closely dependent on the storage time and temperature, enabling to establish a correlation between the number of residual carriers and the freshness of perishable products. Taking KZnF3:Mn2+ as a model material, the light‐storage‐based TTI technology shows excellent recyclability, reliability, and environmental stability. This work reveals great potentials of PersL phosphors as information recording materials in advanced TTI application and next‐generation biological detection technology.

Manipulation of the ratio of Li+/Zn2+ on the structure and persistent luminescence property of Li2Zn0.9992Ge3O8:0.08%Cr3+

AbstractLong persistent luminescence (LPL) materials have been widely applied and investigated in the fields of night‐safe, bio‐fluorescent labeling, and optical anti‐counterfeiting because of their unique properties of delayed luminescence. In this work, the focus of this research is to significantly improve the LPL properties of Li2Zn0.9992Ge3O8:0.08%Cr3+ by adjusting the ratio of Li+/Zn2+. On the one hand, when Li+:Zn2+ < 2:1 (Li1.97Zn1.0292Ge3O8:0.08%Cr3+), a deep‐red LPL is produced in the 650–900 nm band for more than 50 h, which is 2.5 times longer than that without regulation. From another perspective, when Li+:Zn2+ > 2:1 (Li2.01Zn0.9892Ge3O8:0.08%Cr3+), the intensity of LPL is enhanced about four times compared to unregulated. The relationship between traps and LPL was comprehensively investigated by analyzing thermoluminescence spectra. Biological tissue penetration experiments were performed and a set of anti‐counterfeit labels was designed. This research will provide guidance for the design of a novel persistent phosphor for the desired trap depth.

X-ray excited Mn2+-doped persistent luminescence materials with biological window emission for in vivo bioimaging

In recent years, persistent luminescence materials (PLMs) excited by X-rays and emitting in biological windows have received extensive attention in the field of high-sensitivity bioimaging. Transition metal Mn2+ is an ideal emission center, but few studies focus on Mn2+-doped PLMs with X-ray excitation and biological window emission. Here, we report a Mn2+-doped PLM, LiYGeO4:Mn2+ (LYGM), with excellent biological window persistent luminescence emission. After excitation by UV, LYGM produces a durable biological window of persistent luminescence emission at 660 nm for up to 20 h. More importantly, LYGM can be repeatedly excited by X-rays, resulting in long-term biological window persistent luminescence emission. In addition, we obtain LYGM around 200 nm in diameter by ball milling and centrifugation and improve its biocompatibility by surface modification to apply it to in vivo imaging in mice. After LYGM are injected into mice through the tail vein, in situ excitation of X-rays can be achieved. After the persistent luminescence decays, LYGM can be re-excited for repeated imaging. Therefore, LYGM shows potential prospects for in vivo deep tissue and long-term bioimaging.

Oxygen-vacancy rich in melilite to modulate the persistent luminescence for multi-functional applications

Due to the simplicity of vacancy creation, Eu2+-doped melilite is an outstanding persistent luminescence (PersL) material with a continuing glow lifetime of more than several hours.

Colour evolution of dynamic persistent luminescence of Zn3Ga2Ge2O10:Cr3+,Mn2+ phosphors for advanced anti-counterfeiting

The ZGGO:Cr,Mn phosphors exhibit color-changeable photoluminescence and persistent luminescence via excitation wavelength and temperature management, showing the enormous potential for anti-counterfeiting and information storage applications.

Toward color variation of long persistent luminescence in Pr3+-doped garnet transparent ceramic phosphors

Pr3+-doped garnet transparent ceramics for night-vision illumination applications, exhibiting distinct persistent luminescence colors via various relaxation processes, have been successfully prepared for the first time.

Recent advances in the anti-counterfeiting applications of long persistent phosphors.

Counterfeit products have infiltrated numerous regions worldwide, causing substantial damage to the financial interests of individuals, businesses, and countries. Moreover, counterfeit goods can pose a severe risk to human health. Therefore, it is crucial to develop effective anti-counterfeiting methods and authentication technologies. Persistent luminescence (PersL) materials show great potential for anti-counterfeiting applications due to their distinctive spatial and temporal dynamic spectrum performance. The unique luminescence properties of PersL materials enable the creation of optical codes with high capacity. In this perspective, we provide a summary of the latest advancements in anti-counterfeiting technology using long persistent phosphors. We discuss the various construction strategies of optical codes for anti-counterfeiting, which include multicolor luminescence, orthogonal luminescence, dynamic luminescence, and stimulus-response luminescence. In addition, we explore the mechanisms of PersL-based anti-counterfeiting materials and consider potential areas for future development to expand the applications of persistent phosphors.

Co-doped long persistent luminescence materials LiSr3SiO4Cl3:Eu2+,Ln3+ (Ln = Dy, Ho, Er): construction and verification of VRBE and HRBE scheme and their multifunctional applications

The construction and verification of the VRBE and HRBE scheme and the applications of novel long persistent luminescence materials LiSr3SiO4Cl3:Eu2+,Ln3+ (Ln = Dy, Ho, Er).

Insights into blue-light activated red-emitting persistent luminescence from Pr3+-doped phosphors.

In recent years, a series of persistent luminescence materials excitable by blue light have been developed and widely used in many fields such as optical information storage, AC-LEDs, anti-counterfeiting and bio-imaging. However, it is still a long-standing challenge to develop a superior red-emitting persistent phosphor that can be efficiently excited by blue light. In this work, a novel blue-light excited red-emitting persistent phosphor CaCd2Ga2Ge3O12:Pr3+ was successfully synthesized by using a solid-state method, showing excellent luminescence properties. Moreover, the phase purity, crystal structure, photoluminescence spectra, afterglow emission spectra, and three-dimensional thermoluminescence spectrum were successfully investigated. Under 294 nm excitation, photoluminescence spectra show a single orange emission and a series of peaks centered at 492, 537, 568, 614 and 664 nm, which correspond to the 3P0 → 3H4, 3P0 → 3H5, 3P2 → 3H6, 1D2 → 3H4, and 3P0 → 3F2 transitions of Pr3+, respectively. Interestingly, after blue light excitation, the afterglow luminescence exhibits red long emission, which is attributed to the 1D2 → 3H4 transition of Pr3+. Through thermoluminescence spectra and three-dimensional thermoluminescence spectra, we analyze the reasons for the different colors of photoluminescence and afterglow luminescence. The results imply that there are two types of traps, and the depth of shallow traps and deep traps is calculated to be 0.684 and 0.776 eV, respectively. It is worth noting that the photoluminescence is attributed to the 4f2 → 4f5d and f → f transitions of Pr3+, and the afterglow luminescence is ascribed to a tunneling-related process and the transition of electrons from the valence band to the conduction band. The obtained red-emitting persistent phosphors provide a promising pathway toward AC-LEDs, multi-cycle bio-imaging and other fields.

UV-A,B,C Emitting Persistent Luminescent Materials

The nearly dormant field of persistent luminescence has gained fresh impetus after the discovery of strontium aluminate persistent luminescence phosphor in 1996. Several efforts have been put in to prepare efficient, long decay, persistent luminescent materials which can be used for different applications. The most explored among all are the materials which emit in the visible wavelength region, 400-650 nm, of the electromagnetic spectrum. However, since 2014, the wavelength range is extended further above 650 nm for biological applications due to easily distinguishable signal between luminescent probe and the auto-fluorescence. Recently, UV-emitting persistent materials have gained interest among researchers' due to their possible application in information storage, phototherapy and photocatalysis. In the present review, we summarize these recent developments on the UV-emitting persistent luminescent materials to motivate young minds working in the field of luminescent materials.

Achieving Persistent Luminescence Performance Based on the Cation-Tunable Trap Distribution.

Deep-red persistent luminescence (PersL) materials have promising applications in fluorescence labeling and tracking. PersL spectral range and PersL duration are considered to be the key factors driving the development of high-performance deep-red PersL materials. To address these two key issues, the performance of PersL materials was continually optimized by doping with cations (Si4+ and Al3+ ions), relying on the material of Li2ZnGe3O8:Cr3+ from the previous work of our group, and a 4.8-fold increase in PersL radiation spectrum intensity and more than twice the PersL duration was achieved (PersL duration up to 47 h). Ultimately, the obtained PersL materials are used to demonstrate their potential use in multi-level anti-counterfeiting, tracking and localization, respectively. This study provides a unique and novel entry point for achieving high-performance PersL materials by optimizing the PersL material host to modulate the electronic structure.

UV-light activated blue-emitting persistent luminescence of CaYGaO4:Bi3+ suitable for high-temperature environment

The persistent luminescence (PersL) materials suitable for high-temperature environments have attracted extensive attention in recent years. Herein, we have reported a novel long-persistent luminescent material of CaYGaO4:Bi3+, with a peak wavelength of 430 nm and a duration of more than 40 min at room temperature at the 0.32 mcd/m2 threshold value after UV irradiation. A series of thermoluminescence measurements reveal that the CaYGaO4:Bi3+ phosphor has abundant shallow and deep traps with a wide range of distribution. In addition, we utilize the ion substitution strategy of Sr2+ partially replacing Ca2+ ions to increase the shallow trap concentration, so as to improve the performance of PersL at room temperature. More importantly, we investigate the PersL performance of CaYGaO4:Bi3+ phosphor at high-temperature environment. As the result demonstrates, when the ambient temperature is in the high-temperature range (450 K–600 K), the phosphor has more obvious brightness. Finally, we take advantage of the phosphor to carry out a demonstration experiment and obtain a set of temperature-related color conversion images, which unequivocally signifies that the phosphor has broad application prospects in anti-counterfeit fields and emergency indicator marks in high-temperature and harsh environments.

Organic persistent luminescence imaging for biomedical applications

Persistent luminescence is a unique visual phenomenon that occurs after cessation of excitation light irradiation or following oxidization of luminescent molecules. The energy stored within the molecule is released in a delayed manner, resulting in luminescence that can be maintained for seconds, minutes, hours, or even days. Organic persistent luminescence materials (OPLMs) are highly robust and their facile modification and assembly into biocompatible nanostructures makes them attractive tools for in vivo bioimaging, whilst offering an alternative to conventional fluorescence imaging materials for biomedical applications. In this review, we give attention to the existing limitations of each class of OPLM-based molecular bioimaging probes based on their luminescence mechanisms, and how recent research progress has driven efforts to circumvent their shortcomings. We discuss the multifunctionality-focused design strategies, and the broad biological application prospects of these molecular probes. Furthermore, we provide insights into the next generation of OPLMs being developed for bioimaging techniques.