Solar-blind ultraviolet-C persistent luminescence phosphors

Smart windows based on ultraviolet-B persistent luminescence phosphors for bacterial inhibition and food preservation

Herein, ultraviolet B (UVB) persistent luminescence phosphors containing SrAl12O19: Ce3+, Sc3+ nanoparticles were reported. Thermoluminescence (TL) spectrum analysis reveals that the shallow trap induced by Sc3+ co-doping plays an important role in photoluminescence persistent luminescence (PersL) development, while the deep trap dominates the generation of optical stimulated luminescence (OSL). Owing the appearance of deep trap, the OSL is observed under light (700 nm - 900 nm) excitation. UVB luminescence exerts good bactericidal effects on pathogenic bacteria involved in the process of food spoilage. Thus, the smart window with SrAl12O19: Ce3+, Sc3+/PDMS produces UVB PersL to efficiently inactivate Escherichia coli and Staphylococcus aureus. In addition, the presence of the smart window delays the critical point of pork decay, and greatly reduces the time of pork spoilage. It maximizes the convenience of eradicating bacteria and preserving food, thus offering a fresh perspective on the use of UV light for food sterilization and preservation.

Pushing Trap-Controlled Persistent Luminescence Materials toward Multi-Responsive Smart Platforms: Recent Advances, Mechanism, and Frontier Applications

Smart stimuli-responsive persistent luminescence materials, combining the various advantages and frontier applications prospects, have gained booming progress in recent years. The trap-controlled property and energy storage capability to respond to external multi-stimulations through diverse luminescence pathways make them attractive in emerging multi-responsive smart platforms. This review aims at the recent advances in trap-controlled luminescence materials for advanced multi-stimuli-responsive smart platforms. The design principles, luminescence mechanisms, and representative stimulations, i.e., thermo-, photo-, mechano-, and X-rays responsiveness, are comprehensively summarized. Various emerging multi-responsive hybrid systems containing trap-controlled luminescence materials are highlighted. Specifically, temperature dependent trapping and de-trapping performance is discussed, from extreme-low temperature to ultra-high temperature conditions. Emerging applications and future perspectives are briefly presented. It is hoped that this review would provide new insights and guidelines for the rational design and performance manipulation of multi-responsive materials for advanced smart platforms.

Enabling Broadband Solar-Blind UV Photodetection by a Rare-Earth Doped Oxyfluoride Transparent Glass-Ceramic

Oxyfluoride transparent glass-ceramics (GC) are widely used as the matrix for rare-earth (RE) ions due to their unique properties such as low phonon energy, high transmittance, and high solubility for RE ions. Tb3+ doped oxyfluoride glasses exhibit a large absorption cross section for ultraviolet (UV) excitation, high stability, high photoluminescence quantum efficiency, and sensitive spectral conversion characteristics, making them promising candidate materials for use as the spectral converter in UV photodetectors. Herein, a Tb3+ doped oxyfluoride GC is developed by using the melt-quenching method, and the microstructure and optical properties of the GC sample are carefully investigated. By combining with a Si-based photo-resistor,a solar-blind UV detector is fabricated, which exhibits a significant photoelectric response with a broad detection range from 188 to 400 nm. The results indicate that the designed UV photodetector is of great significance for the development of solar-blind UV detectors.

Molten Salt Synthesized CaTa4O11:Er3+/Yb3+ with Superior Upconversion Luminescence

Low phonon tantalate-based phosphors with a layer structure are considered to have excellent upconversion luminescence (UCL) intensity, which could be reduced due to the existence of impure phase defects and inappropriate doped rare earth ions. To improve their UCL performance, we have prepared single-phase CaTa4O11:Er3+/Yb3+ samples by a molten salt synthesis (MSS) using KCl as the reaction medium and compared its UCL properties with counterparts made by a conventional solid-state reaction (SSR) in this study. We have demonstrated that the MSS samples have a much higher UCL intensity under 980 nm laser excitation than the SSR ones due to accurate replacement of Ca2+ sites by Er3+/Yb3+ in high-purity single-phase MSS samples. We have further enhanced the green UCL intensity of the MSS samples by 1.57 times via acid picking (AP). Under 980 nm laser excitation at a high powder density of 61.3 W/cm2, the green UCL intensity of the MSS-AP samples can reach 3.72 times that of the SSR-AP samples. For potential luminescence thermometry applications, the maximum absolute sensitivity (SA) of the MSS-AP samples reaches 0.01316 K-1 at 501 K based on the luminescence intensity ratio. This study shows that CaTa4O11:Er3+/Yb3+ phosphors prepared by the MSS method are single-phase samples with excellent pure green UCL as a suitable temperature sensing material.

High-Confidentiality X-Ray Imaging Encryption Using Prolonged Imperceptible Radioluminescence Memory Scintillators

X-ray imaging plays an increasingly crucial role in clinical radiography, industrial inspection, and military applications. However, current X-ray imaging technologies have difficulty in protecting against information leakage caused by brute force attacks via trial-and-error. Here high-confidentiality X-ray imaging encryption by fabricating ultralong radioluminescence memory films composed of lanthanide-activated nanoscintillators (NaLuF4 : Gd3+ or Ce3+ ) with imperceptible purely-ultraviolet (UV) emission is reported. Mechanistic investigations unveil that ultralong X-ray memory is attributed to the long-lived trapping of thermalized charge carriers within Frenkel defect states and subsequent slow release in the form of imperceptible radioluminescence. The encrypted X-ray imaging can be securely stored in the memory film for more than 7 days and optically decoded by perovskite nanocrystal. Importantly, this encryption strategy can protect X-ray imaging information against brute force trial-and-error attacks through the perception of lifetime change in the persistent radioluminescence. It is further demonstrated that the as-fabricated flexible memory film enables achieving of 3D X-ray imaging encryption of curved objects with a high spatial resolution of 20 lp/mm and excellent recyclability. This study provides valuable insights into the fundamental understanding of X-ray-to-UV conversion in nanocrystal lattices and opens up a new avenue toward the development of high-confidential 3D X-ray imaging encryption technologies.

Persistent luminescent nanophosphors for applications in cancer theranostics, biomedical, imaging and security

The extraordinary and unique properties of persistent luminescent (PerLum) nanostructures like storage of charge carriers, extended afterglow, and some other fascinating characteristics like no need for in-situ excitation, and rechargeable luminescence make such materials a primary candidate in the fields of bio-imaging and therapeutics. Apart from this, due to their extraordinary properties they have also found their place in the fields of anti-counterfeiting, latent fingerprinting (LPF), luminescent markings, photocatalysis, solid-state lighting devices, glow-in-dark toys, etc. Over the past few years, persistent luminescent nanoparticles (PLNPs) have been extensively used for targeted drug delivery, bio-imaging guided photodynamic and photo-thermal therapy, biosensing for cancer detection and subsequent treatment, latent fingerprinting, and anti-counterfeiting owing to their enhanced charge storage ability, in-vitro excitation, increased duration of time between excitation and emission, low tissue absorption, high signal-to-noise ratio, etc. In this review, we have focused on most of the key aspects related to PLNPs, including the different mechanisms leading to such phenomena, key fabrication techniques, properties of hosts and different activators, emission, and excitation characteristics, and important properties of trap states. This review article focuses on recent advances in cancer theranostics with the help of PLNPs. Recent advances in using PLNPs for anti-counterfeiting and latent fingerprinting are also discussed in this review.

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.

Narrowband Ultraviolet-B Persistent Luminescence in an Indoor-Lighting Environment through Energy Transfer from Host Excitons to Gd3+ Emitters in ScPO4

Narrowband ultraviolet-B (NB-UVB) luminescent materials are characterized by high photon energy, narrow spectral width, and visible-blind emission, thus holding great promise for photochemistry and photomedicine. However, most NB-UVB phosphors developed so far are photoluminescent, where continuous external excitation is needed. Herein, we realize NB-UVB persistent luminescence (PersL) in an indoor-lighting environment by exploiting the interaction between self-trapped/defect-trapped excitons and Gd3+ emitters in ScPO4. The phosphor shows a self-luminescing feature with a peak maximum at 313 nm with a time duration of >24 h after ceasing X-ray irradiation, which can be clearly imaged by an UVB camera in a bright environment. Spectroscopic and theoretical approaches reveal that thermo- and photo-stimulations of energies trapped at intrinsic lattice defects followed by energy transfer to Gd3+ emitters account for the emergence of the afterglow. The present results can initiate more exploration of NB-UVB PersL phosphors for emerging applications in secret optical tagging and phototherapy.

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 10 h), 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.

Dynamic anti-counterfeiting and information encryption of Sr3Y2Ge3O12: Tb3+, Er3+ phosphor via carriers filling and release processes

Complex and high-security-level anti-counterfeiting strategies with multiple luminescent modes are extremely critical for meeting the requirement of constantly developing information storage and information security. In this work, Tb³⁺ ions doped Sr₃Y₂Ge₃O₁₂ (SYGO) and Tb³⁺/Er³⁺ co-doped SYGO phosphors are successfully fabricated and are unitized for anti-counterfeiting and information encoding under distinct stimuli sources. The green photoluminescence (PL), long persistent luminescence (LPL), mechano-luminescence (ML), and photo-stimulated luminescence (PSL) behaviors are respectively observed under the stimuli of ultraviolet (UV), thermal disturbance, stress, and 980 nm diode laser. Based on the time-dependence of the filling and releasing rate of the carriers from the shallow traps, the dynamic information encryption strategy is proposed by simply changing the UV pre-irradiation time or shut-off time. Moreover, a tunable color from green to red is realized by prolonging the 980 nm laser irradiation time, which is attributed to the elaborate cooperation of the PSL and upconversion (UC) behaviors. The anti-counterfeiting method based on SYGO: Tb³⁺ and SYGO: Tb³⁺, Er³⁺ phosphors herein possess an extremely high-security level with attractive performance for designing advanced anti-counterfeiting technology.

Shortwave Ultraviolet Persistent Luminescence of Sr2MgSi2O7: Pr3

Currently, extensive research activities are devoted to developing persistent phosphors which extend beyond the visible range. In some emerging applications, long-lasting emission of high-energy photons is required; however, suitable materials for the shortwave ultraviolet (UV-C) band are extremely limited. This study reports a novel Sr₂MgSi₂O₇ phosphor doped with Pr³⁺ ions, which exhibits UV-C persistent luminescence with maximum intensity at 243 nm. The solubility of Pr³⁺ in the matrix is analysed by X-ray diffraction (XRD) and optimal activator concentration is determined. Optical and structural properties are characterised by photoluminescence (PL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) spectroscopy techniques. The obtained results expand the class of UV-C persistent phosphors and provide novel insights into the mechanisms of persistent luminescence.

Recent Developments of Microscopic Study for Lanthanide and Manganese Doped Luminescent Materials

Luminescent materials are indispensable for applications in lighting, displays and photovoltaics, which can transfer, absorb, store and utilize light energy. Their performance is closely related with their size and morphologies, exact atomic arrangement, and local configuration about photofunctional centers. Advanced electron microscopy-based techniques have enabled the possibility to study nanostructures with atomic resolution. Especially, with the advanced micro-electro-mechanical systems, it is able to characterize the luminescent materials at the atomic scale under various environments, providing a deep understanding of the luminescent mechanism. Accordingly, this review summarizes the recent achievements of microscopic study to directly image the microstructure and local environment of activators in lanthanide and manganese (Ln/Mn²⁺ )-doped luminescent materials, including: 1) bulk materials, the typical systems are nitride/oxynitride phosphors; and 2) nanomaterials, such as nanocrystals (hexagonal-phase NaLnF₄ and perovskite) and 2D nanosheets (Ca₂ Ta₃ O₁₀ and MoS₂ ). Finally, the challenges and limitations are highlighted, and some possible solutions to facilitate the developments of advanced luminescent materials are provided.

Multichannel Control of PersL/Upconversion/Down-Shifting Luminescence in a Single Core-Shell Nanoparticle for Information Encryption

Persistent luminescence (PersL) has been attracting substantial attention in diverse frontier applications such as optical information security and in vivo bioimaging. However, most of the reported PersL emissions are based on the dopants instead of the host matrix, which also plays an important role. In addition, there are few works on the PersL-based multifunctional nanoplatform in nanosized materials. Here, we report a class of novel nanostructure designs with PersL, upconversion, and down-shifting luminescence to realize the fine-tuning of emission colors under different excitation modes including steady-state irradiation, time-gating, and PersL generation. Blue, orange, and green emissions were easily achieved in such a single nanoparticle under suitable excitation modes. Moreover, the physical origin of the PersL of the CaF₂ matrix was discussed by simulating the energy band structure with Ca_xF_y defects. Our results provide new opportunities for the design of a new class of multifunctional materials, showing great promise in the field of information encryption security and multilevel anticounterfeiting.

Multiple Coordination of Chromium Ion Luminescence: A Strategy for Designing Ultra-broadband NIR Long Persistent Luminescent Materials

Near-infrared (NIR) long persistent luminescent (LPL) materials have attracted the interest of many researchers as they have potential applications in many aspects. However, majority of studies on Cr³⁺ ion-doped LPL materials have focused on Cr³⁺ in an octahedral site, and the luminescence is limited to the short-wavelength NIR-I region (700-900 nm), which is detrimental to fully explore Cr³⁺ ion-doped LPL materials with potential applications. In this work, a novel ultra-broadband NIR LPL material, Na₂CaGe₆O₁₄ (NCGO):x%Cr³⁺, was successfully designed and synthesized, covering the luminescence range of 600-1200 nm and having the best afterglow duration of more than 10 h. Combining the luminescence lifetime with the low-temperature spectrum, it was concluded that the luminescence of NCGO:Cr³⁺ consists of the co-emission of Cr³⁺ in octahedra and tetrahedra. And it was confirmed by electron paramagnetic resonance (EPR) spectrum and X-ray absorption near-edge spectrum (XANES). The application prospects of NCGO:x%Cr³⁺ in many aspects were investigated in detail. This work could not only give a reference for researchers to study Cr³⁺ luminescence in multiple coordination but also provide a new strategy for obtaining new ultra-broadband NIR LPL materials.

Bright UV-C Phosphors with Excellent Thermal Stability-Y1-xScxPO4 Solid Solutions

The structural and luminescence properties of undoped Y_1-xSc_xPO₄ solid solutions have been studied. An intense thermally stable emission with fast decay (τ_1/e ~ 10^-7 s) and a band position varying from 5.21 to 5.94 eV depending on the Sc/Y ratio is detected and ascribed to the 2p O-3d Sc self-trapped excitons. The quantum yield of the UV-C emission, also depending on the Sc/Y ratio, reaches 34% for the solid solution with x = 0.5 at 300 K. It is shown by a combined analysis of theoretical and experimental data that the formation of Sc clusters occurs in the solid solutions studied. The clusters facilitate the creation of energy wells at the conduction band bottom, which enables deep localization of electronic excitations and the creation of luminescence centers characterized by high quantum yield and thermal stability of the UV-C emission.

Design of need-based phosphors and scintillators by compositional modulation in the ZnGa2-xAlxO4:Cr3+ spinel: pure compound versus solid solutions

Materials that can depict persistent deep red light under both ultraviolet (UV) and X-ray illumination can be a boon to sustainable economy, particularly for optical imaging, solid state lighting, and anticounterfeiting applications. Herein, we have made a series of compounds starting from ZnGa₂O₄:Cr³⁺ to ZnAl₂O₄:Cr³⁺ (individual spinel) by substituting the varied concentration of Al³⁺ in place of Ga³⁺ in ZnGa_2-xAl_xO₄:Cr³⁺ (solid solution). By virtue of the structural and defect engineering doping strategy, the photo and radioluminescence are expected to be improved. Both Cr and Al doping was found to be energetically favorable in ZnGa₂O₄, where the same does not hold true for Ga doping in ZnAl₂O₄, as indicated by the DFT-calculated defect formation energies. There seems to be ordering around the dopant ion in the solid solutions compared to either ZnGa₂O₄ or ZnAl₂O₄ and is also reflected to as lower persistent luminescence (PerL) lifetimes. PerL under UV, in general. was found to be lower with the enhancement in the Al³⁺ content endowed by the formation of Cr-Cr ion pair, lower probability of antisite formation, and widening band gap. On the other hand, X-ray excited emission enhances in the solid solution due to the decrease in cation inversion and associated defects. Confocal Microscopy showed that larger particles depicted much brighter deep red emission but failed to percolate to the human cells to a detectable limit; hence, future work is needed for the functionalization of the ZnGa_2-xAl_xO₄:Cr³⁺ spinel. This work could be of great implication in designing need-based materials, where UV and X-ray excitation is required, for deep red emission with persistent characteristics from chromium-doped spinels.

Visible-to-ultraviolet-C upconverted photon for multifunction via Ca2SiO4:Pr3

The ultraviolet C (UVC) photon plays a key role in a broad spectrum of fields. With the implementation of the Minamata Convention, searching for a new way to achieve UVC light is highly desired. Here we develop a material of Ca₂SiO₄:Pr³⁺ that can emit UVC light upon excitation of a 450-nm laser or even a very cheap 450-nm LED, a fact confirmed by using a solar blind camera to capture UVC emission from Ca₂SiO₄:Pr³⁺. In addition, smart anti-counterfeiting and inactivation of Bacillus subtilis applications using Ca₂SiO₄:Pr³⁺ are also confirmed.

Portable visual assay of Bacillus anthracis biomarker based on ligand-functionalized dual-emission lanthanide metal-organic frameworks and smartphone-integrated mini-device

A single-functionalized ligand single-Ln³⁺ based dual-emission Ln-MOF fluorescent sensor was established for portable and visual dipicolinic acid (DPA, Bacillus anthracis biomarker) detection. First, a theory calculation-based prediction model was developed for designing single-functionalized ligand single-Ln³⁺ dual-emission Ln-MOFs. The model consisted of three calculation modules: intramolecular hydrogen bonds, excited state energy levels, and coordination stability with Ln³⁺ of ligands. Tb³⁺ and Eu³⁺ were selected as metal luminescence centers, PTA-X (PTA: p-phthalic acid, X = NH₂, CH₃, H, OH) with different functional groups as one-step functionalization ligands, and the luminescent feature of four Tb-MOFs and four Eu-MOFs was predicted with the model. Coupled with prediction results and experimental verification results, Tb-PTA-OH was rapidly determined to be the sole dual-emission Ln-MOF. Then, Tb-PTA-OH was applied to DPA detection by ratiometric fluorescence, and an ultra-low limit of detection (13.4 nM) was obtained, which is much lower than the lowest anthrax infectious dose (60 μM). A portable visual assay method based on paper-microchip and smartphone integrated mini-device was further established (limit of qualification 0.48 μM). A new sensing mechanism and a "triple gates" selectivity mechanism to DPA were proposed. This work reveals guidelines for material design and mini-device customization in detecting hazardous substances.

Nonvolatile modulation of luminescence in perovskite oxide thin films by ferroelectric gating

Nonvolatile and giant modulation of luminescence can be realized by the ferroelectric gating effect in a Ga³⁺/Pr³⁺ co-doped BaTiO₃ ultra-thin film epitaxially grown on a [Pb(Mg_1/3Nb_2/3)O₃]_0.7-[PbTiO₃]_0.3 single-crystallized substrate. The change behavior of the emission intensity matches that of the ferroelectric polarization hysteresis loop with a giant enhancement of over 13 times with negative polarization orientation. The interaction of O^2- at the O2p orbital in the valence band and Pr³⁺ with injected holes by the ferroelectric gating effect promotes the formation of excited state O^-, Pr⁴⁺, or Pr^3+q. This ferroelectric gating method can promote the development of controllable photo-, electroluminescent, and other optoelectronic devices for display, sensing, communication, and so on.

Mechanism of the trivalent lanthanides' persistent luminescence in wide bandgap materials

The trivalent lanthanides have been broadly utilized as emitting centers in persistent luminescence (PersL) materials due to their wide emitting spectral range, which thus attract considerable attention over decades. However, the origin of the trivalent lanthanides' PersL is still an open question, hindering the development of excellent PersL phosphors and their broad applications. Here, the PersL of 12 kinds of the trivalent lanthanides with the exception of La³⁺, Lu³⁺, and Pm³⁺ is reported, and a mechanism of the PersL of the trivalent lanthanides in wide bandgap hosts is proposed. According to the mechanism, the excitons in wide bandgap materials transfer their recombination energy to the trivalent lanthanides that bind the excitons, followed by the generation of PersL. During the PersL process, the trivalent lanthanides as isoelectronic traps bind excitons, and the binding ability is not only related to the inherent arrangement of the 4f electrons of the trivalent lanthanides, but also to the extrinsic ligand field including anion coordination and cation substitution. Our work is believed to be a guidance for designing high-performance PersL phosphors.

Persistent phosphors for luminous paints: A review

The paper briefly reports the fundamental scientific principles and landmarks in the field of luminescence and further enlightens the importance of persistent phosphor that is now widely used in luminous paints. Its main focus is on phosphorescence that makes use of lanthanides that have gained paramount importance in various cross-sections of luminescent applications.. Both inorganic and organic afterglow materials, synthesis and characterization along with skilled researchers' essential updates on emerging trends and efforts are elucidated at length. It exclusively reviews the red/green/blue organic/inorganic/hybrid phosphorescent materials and the latest advances in the development of novel long afterglow materials that can accelerate the green technology in the world of luminescence.

Recent Advances on Host-Guest Material Systems toward Organic Room Temperature Phosphorescence

The design and characterization of purely organic room-temperature phosphorescent (RTP) materials for optoelectronic applications is currently the focus of research in the field of organic electronics. Particularly, with the merits of preparation controllability and modulation flexibility, host-guest material systems are encouraging candidates that can prepare high-performance RTP materials. By regulating the interaction between host and guest molecules, it can effectively control the quantum efficiency, luminescent lifetime, and color of host-guest RTP materials, and even produce RTP emission with stimuli-responsive features, holding tremendous potential in diverse applications such as encryption and anti-counterfeiting, organic light-emitting diodes, sensing, optical recording, etc. Here a roundup of rapid achievement in construction strategies, molecule systems, and diversity of applications of host-guest material systems is outlined. Intrinsic correlations between the molecular properties and a survey of recent significant advances in the development of host-guest RTP materials divided into three systems including rigid matrix, exciplex, and sensitization are presented. Providing an insightful understanding of host-guest RTP materials and offering a promising platform for high throughput screening of RTP systems with inherent advantages of simple material preparation, low-cost, versatile resource, and controllably modulated properties for a wide range of applications is intended.

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

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

X-ray-activated persistent luminescence nanomaterials for NIR-II imaging

Persistent luminescence is not affected by background autofluorescence, and thus holds the promise of high-contrast bioimaging. However, at present, persistent luminescent materials for in vivo imaging are mainly bulk crystals characterized by a non-uniform size and morphology, inaccessible core-shell structures and short emission wavelengths. Here we report a series of X-ray-activated, lanthanide-doped nanoparticles with an extended emission lifetime in the second near-infrared window (NIR-II, 1,000-1,700 nm). Core-shell engineering enables a tunable NIR-II persistent luminescence, which outperforms NIR-II fluorescence in signal-to-noise ratios and the accuracy of in vivo multiplexed encoding and multilevel encryption, as well as in resolving mouse abdominal vessels, tumours and ureters in deep tissue (~2-4 mm), with up to fourfold higher signal-to-noise ratios and a threefold greater sharpness. These rationally designed nanoparticles also allow the high-contrast multiplexed imaging of viscera and multimodal NIR-II persistent luminescence-magnetic resonance-positron emission tomography imaging of murine tumours.

Ultraviolet-C persistent luminescence from the Lu2SiO5:Pr3+ persistent phosphor for solar-blind optical tagging

Visible and infrared persistent phosphors have gained considerable attention in recent years and are being widely used as glow-in-the-dark materials in dark environments. In contrast, the progress in persistent phosphors emitting at the other end of the spectrum, i.e., the shorter-wavelength ultraviolet-C (UVC; 200-280 nm), is rather slow. Here we report the design and synthesis of a well-performing Pr3+-doped UVC emissive persistent phosphor, Lu2SiO5:Pr3+, which exhibits intense UVC persistent luminescence peaking at 270 nm and a long persistence time of more than 12 h after excitation with a 254 nm UV lamp. Besides, the UVC persistent luminescence of a UV pre-irradiated sample can be repeatedly revived after repeated short-illumination with low-energy white light via a process called photostimulated persistent luminescence. Owing to the distinct spectral features of UVC light and the self-sustained luminescence properties, the UVC persistent luminescence of the Lu2SiO5:Pr3+ persistent phosphor can be clearly monitored and imaged using a corona camera in bright environments including direct sunlight and indoor light. The Lu2SiO5:Pr3+ persistent phosphor is expected to find promising applications in the covert optical tagging field.

Insights into the Microstructures and Energy Levels of Pr3+-Doped YAlO3 Scintillating Crystals

Trivalent praseodymium (Pr3+)-doped materials have been extensively used in high-resolution laser spectroscopy, owing to their outstanding conversion efficiencies of plentiful transitions in the visible laser region. However, to clarify the microstructure and energy transfer mechanism of Pr3+-doped host crystals is a challenging topic. In this work, the stable structures of Pr3+-doped yttrium orthoaluminate (YAlO3) have been widely searched based on the CALYPSO method. A novel monoclinic structure with the Pm group symmetry is successfully identified. The Pr3+ impurity can precisely occupy the Y3+ position and get incorporated into the YAlO3 (YAP) host crystal with a Pr3+ concentration of 6.25%. The result of the electronic band structure reveals a 3.62 eV band gap, which suggests a semiconductor character of YAP:Pr. Using our developed well-established parametrization matrix diagonalization (WEPMD) method, we have systematically analyzed the energy level scheme and proposed a set of newly improved parameters. Additionally, the energy transfer mechanism of YAP:Pr is clarified by deciphering the numerical electric dipole and magnetic dipole transitions. The popular red emission at 653 nm is assigned to the transition 3P0 → 3F2, while the transition 3P0 → 3H4 with a large branching ratio is predicted to be a good laser channel. Many promising emission lines for laser actions are also obtained in the visible light region. Our results not only provide important insights into the energy transfer mechanisms of rare-earth ion-doped materials but also pave the way for the implementation of new types of laser devices.

Gd3+-activated narrowband ultraviolet-B persistent luminescence through persistent energy transfer

This work reports the realization of Gd3+ persistent luminescence in the narrowband ultraviolet-B (NB-UVB; 310-313 nm) through persistent energy transfer from a sensitizer of Pr3+, Pb2+ or Bi3+. We propose a general design concept to develop Gd3+-activated NB-UVB persistent phosphors from Pr3+-, Pb2+- or Bi3+-activated ultraviolet-C (200-280 nm) or ultraviolet-B (280-315 nm) persistent phosphors, leading to the discovery of ten Gd3+ NB-UVB persistent phosphors such as Sr3Gd2Si6O18:Pr3+, Sr3Gd2Si6O18:Pb2+ and Y2GdAl2Ga3O12:Bi3+ as well as five ultraviolet-B persistent phosphors such as Y3Al2Ga3O12:Pr3+, Sr3Y2Si6O18:Pb2+ and Y3Al2Ga3O12:Bi3+. The persistent energy transfer from the sensitizers to Gd3+ is very efficient and the Gd3+ NB-UVB afterglow can last for more than 10 hours. This study expands the persistent luminescence research to the NB-UVB as well as the broader ultraviolet-B spectral regions. The NB-UVB persistent phosphors may act as self-sustained glowing NB-UVB radiation sources for dermatological therapy.

Particle size-related limitations of persistent phosphors based on the doped Y3Al2Ga3O12 system

Co-doped Ce³⁺, Cr³⁺ and Pr³⁺ yttrium-aluminium-gallium garnet powders of various sizes were obtained by co-precipitation method. The microstructure and morphology were investigated by XRPD, TEM and gas porosimetry. The luminescence properties were studied by excitation and emission spectra, quantum yield and decay times. Thermoluminescence measurements were performed to evaluate the activation energy, traps redistribution and frequency factor. Limitation in the energy transfer between dopant ions in the small particles, traps depth and surface defects were considered and investigated as responsible for the quenching of persistent luminescence. The phosphors annealed at 1100 °C show the optimal persistent luminescence and nano-particle size.

Ultraviolet-A Persistent Luminescence of a Bi3+-Activated LiScGeO4 Material

Long persistent phosphors (LPPs) with ultraviolet (UV) luminescence have great potential for application in the fields of biomedicine, environmental, and catalysis. However, it is currently limited by the design and development of remarkable UV LPPs with a suitable spectral region and an ultralong afterglow decay time. Herein, we develop a new type of Bi³⁺-activated LiScGeO₄ LPP, which exhibits bright ultraviolet-A (UVA) persistent luminescence (PersL). Because of the existence of numerous stabilized effective traps, the as-synthesized phosphors can undergo an ultralong PersL decay time far longer than 12 h. The PersL properties, effective trap depths, distributions, and types, as well as the possible mechanism for the PersL behavior of LiScGeO₄:Bi³⁺, are comprehensively surveyed utilizing PersL excitation spectra, PersL decay analyses, thermoluminescence experiments, and X-ray photoelectron spectroscopy. This work can cover the shortage of LPPs in the UV region and also can lay the foundation for the development of more excellent UV LPPs toward versatile novel applications.

Long-lasting ultraviolet-A persistent luminescence and photostimulated persistent luminescence in Bi3+-doped LiScGeO4phosphor

A UVA emissive LiScGeO₄:Bi³⁺persistent phosphor is developed, which exhibits single-band, long-lasting persistent luminescence and a photostimulated persistent luminescence capability.