Persistent Luminescence Materials Research Articles

Full‐Spectrum Persistent Luminescence Tuning Using All‐Inorganic Perovskite Quantum Dots

AbstractApplications of persistent luminescence phosphors as night or dark‐light vision materials in many technological fields have fueled up a growing demand for rational control over the emission profiles of the phosphors. This, however, remains a daunting challenge. Now a unique strategy is reported to fine‐tune the persistent luminescence by using all‐inorganic CsPbX3 (X=Cl, Br, and I) perovskite quantum dots (PeQDs) as efficient light‐conversion materials. Full‐spectrum persistent luminescence with wavelengths covering the entire visible spectral region is achieved through tailoring of the PeQD band gap, in parallel with narrow bandwidth of PeQDs and highly synchronized afterglow decay owing to the single energy storage source. These findings break through the limitations of traditional afterglow phosphors, thereby opening up opportunities for persistent luminescence materials for applications such as a white‐emitting persistent light source and dark‐light multicolor displays.

Full-Spectrum Persistent Luminescence Tuning Using All-Inorganic Perovskite Quantum Dots.

Applications of persistent luminescence phosphors as night or dark-light vision materials in many technological fields have fueled up a growing demand for rational control over the emission profiles of the phosphors. This, however, remains a daunting challenge. Now a unique strategy is reported to fine-tune the persistent luminescence by using all-inorganic CsPbX3 (X=Cl, Br, and I) perovskite quantum dots (PeQDs) as efficient light-conversion materials. Full-spectrum persistent luminescence with wavelengths covering the entire visible spectral region is achieved through tailoring of the PeQD band gap, in parallel with narrow bandwidth of PeQDs and highly synchronized afterglow decay owing to the single energy storage source. These findings break through the limitations of traditional afterglow phosphors, thereby opening up opportunities for persistent luminescence materials for applications such as a white-emitting persistent light source and dark-light multicolor displays.

A Metal–Organic Supramolecular Box as a Universal Reservoir of UV, WL, and NIR Light for Long‐Persistent Luminescence

AbstractLong persistent luminescence (LPL) materials have a unique photophysical mechanism to store light radiation energy for subsequent release. However, in comparison to the common UV source, white‐light (WL) and near‐infrared (NIR) excited LPL is scarce. Herein we report a metal–organic supramolecular box based on a D–π–A‐type ligand. Owing to the integrated one‐photon absorption (OPA) and two‐photon absorption (TPA) attributes of the ligand, the heavy‐atom effect of the metal center, as well as π‐stacking and J‐aggregation states in the supramolecular assembly, LPL can be triggered by all wavebands from the UV to the NIR region. This novel designed supramolecular kit to afford LPL by both OPA and TPA pathways provides potential applications in anti‐counterfeiting, camouflaging, decorating, and displaying, among others.

A Metal-Organic Supramolecular Box as a Universal Reservoir of UV, WL, and NIR Light for Long-Persistent Luminescence.

Long persistent luminescence (LPL) materials have a unique photophysical mechanism to store light radiation energy for subsequent release. However, in comparison to the common UV source, white-light (WL) and near-infrared (NIR) excited LPL is scarce. Herein we report a metal-organic supramolecular box based on a D-π-A-type ligand. Owing to the integrated one-photon absorption (OPA) and two-photon absorption (TPA) attributes of the ligand, the heavy-atom effect of the metal center, as well as π-stacking and J-aggregation states in the supramolecular assembly, LPL can be triggered by all wavebands from the UV to the NIR region. This novel designed supramolecular kit to afford LPL by both OPA and TPA pathways provides potential applications in anti-counterfeiting, camouflaging, decorating, and displaying, among others.

A new path to design near-infrared persistent luminescence materials using Yb3+-doped rare earth oxysulfides

RE2O2S:Yb3+ and RE2O2S:Yb3+,Ti,Mg2+ near-infrared persistent luminescence materials (RE3+: La, Gd, Y) were designed based on the efficient red-emitting RE2O2S:Eu3+,Ti,Mg2+, due to the similar ground state level positions between Eu3+ and Yb3+. The Y2O2S:Yb3+,Ti,Mg2+ showed the longest near-infrared (~983 nm) persistent luminescence time (~1 h) when excited at the charge transfer transition, demonstrating that Ti,Mg2+ co-doping enhances the persistent luminescence only for the Y2O2S host. The unprecedented relationship between Eu3+ and Yb3+ persistent luminescence opens a new path in the systematic design of efficient Yb3+-activated persistent luminescence materials e.g. Y2O2S:Yb3+,Ti,Mg2+, which present potential for photonic applications such as bioimaging probes.

The red persistent luminescence of (Sr,Ca)AlSiN3:Eu2+ and mechanism different to SrAl2O4:Eu2+,Dy3+

(Sr,Ca)AlSiN3:Eu2+ phosphors have been widely used in phosphor-converted white light emitting diodes. Herein, we reported the strong red persistent luminescence in (Sr,Ca)AlSiN3:Eu2+ under UV light excitation. The Sr0.8Ca0.2AlSiN3:0.15% Eu2+ shows the strongest red persistent luminescence with a peak emission wavelength at ~628 nm and a persistent time of ~9600 s at the 0.32 mcd/m2 threshold value. A new persistent luminescence mechanism, which is different to that of SrAl2O4:Eu2+,Dy3+, was proposed by comparing the thermoluminescence excitation spectrum (TLES) and the photoluminescence excitation spectrum (PLES) of Sr0.8Ca0.2AlSiN3:0.15% Eu2+. The electrons are directly excited from 4f ground states to the conduction band or from valence band to conduction band in (Sr,Ca)AlSiN3:Eu2+; while, in SrAl2O4:Eu2+,Dy3+, they are first excited to 5d level and then stimulated thermal process to the conduction band. The effect of Eu2+ concentration on red persistent luminescence in (Sr,Ca)AlSiN3:Eu2+ were discussed. The proposed mechanism of persistent luminescence can help us to design and find new persistent luminescence materials.

Enantiomer-selective sensing and the light response of chiral molecules coated with a persistent luminescent material.

Pr3+:CaTiO3, a robust persistent luminescent material, was coupled with chiral molecules and Ag nanoparticles (NPs) to construct a Pr3+:CaTiO3@Ag@l-cysteine ternary material that can realize rapid enantiomer selective sensing of l- and d-arginine by making use of the chiral induced spin selectivity (CISS) effect. In addition, long-lifetime photoelectrons excited in the Pr3+:CaTiO3 matrix were effectively transported through a Ag NP "bridge" into the l-cysteine chiral monolayer, due to cooperation between each component in the ternary material.

A comprehensive study of the red persistent luminescence mechanism of Y2O2S:Eu,Ti,Mg.

Y2O2S:Eu,Ti,Mg, a persistent luminescence (PersL) material that exhibits eye-sensitive red emission for longer than 4-5 h, has attracted much attention and has been intensively researched over the past decade. If it is figured out how to prolong its decay time for longer than 8 h, the amazing candle-like red PersL performance, once lit, can illuminate a room all night without electricity. However, the PersL mechanism is still confusing, since different investigators have their own unique understanding about it based on their personal experimental observations. In this work, a more comprehensive and detailed investigation of the PersL mechanism is carried out, based on the defect levels induced by Eu, Ti, and Mg impurities and anion vacancies, using first-principles calculations. Our calculated results suggest that the empty spin-down 4f levels of Eu3+ appear in the band gap, while the occupied spin-up 4f levels are just below the valence band maximum (VBM). The 3d levels of Ti4+ are located in the band gap, with the highest levels around 1.4 eV below the conduction band minimum (CBM). Positively charged anion vacancies were found to induce empty defect levels just below the CBM and so could serve as electron trap centers, which prolong the lifetimes of excited electrons and lead to the PersL of the Ti4+ ion. When Eu3+ is co-doped with Ti4+, the energy of the excited Ti4+ ions is transferred to Eu3+. This mechanism can explain well most of the experimental observations that have appeared in the literature over the past decade. The obtained PersL mechanism is very clear in terms of the roles played by most types of defect, so we hope it can provide physical understanding and create intrigue around the idea of practical guidelines for the design of new red PersL materials in the future.

Cluster-Based Metal-Organic Frameworks: Modulated Singlet-Triplet Excited States and Temperature-Responsive Phosphorescent Switch.

Luminescent metal-organic frameworks (MOFs) have received much attention due to their applications in color displays, sensors, and smart materials. However, how to balance the energy distribution between singlet and triplet excited states for a new generation of persistent luminescent MOFs is still a challenging goal. In this work, we report that the construction of cluster-based MOFs can supply an effective way to modulate the fluorescence and room-temperature phosphorescence (RTP) emission based on adjustable π-π stacking, halogen-bonding interaction, and metal-cluster units. Compared to the pristine ligand (5-bromoisophthalic acid) with obvious spin-orbit coupling, Zn5 and Zn3 cluster-based MOFs exhibit tunable photoluminescence (such as fluorescence and RTP wavelength, lifetime, and quantum yield). The ultralong-lived RTP visualization and temperature-dependent luminescence also provide the Zn5 cluster-based MOF as a new type of anticounterfeiting and temperature-responsive phosphorescent switch material. Therefore, this work highlights the first example of cluster-based MOFs as ultralong-lived persistent luminescent materials for tuning singlet and triplet excited states, which may be extended to other similar systems for developing ultralong RTP and delayed fluorescence materials.

Tailoring Trap Depth and Emission Wavelength in Y3Al5- xGa xO12:Ce3+,V3+ Phosphor-in-Glass Films for Optical Information Storage.

Deep-trap persistent luminescent materials, due to their exceptional ability of energy storage and controllable photon release under external stimulation, have attracted considerable attention in the field of optical information storage. Currently, the lack of suitable materials is still the bottleneck that restrains their practical applications. Herein, we successfully synthesized a series of deep-trap persistent luminescent materials Y3Al5- xGa xO12:Ce3+,V3+ ( x = 0-3) with a garnet structure and developed novel phosphor-in-glass (PiG) films containing these phosphors. The synthesized PiG films exhibited sufficiently deep traps, narrow trap depth distributions, high trap density, high quantum efficiency, and excellent chemical stability, which solved the problem of chemical stability at high temperatures in the reported phosphor-in-silicone films. Moreover, the trap depth in the phosphors and PiG films could be tailored from 1.2 to 1.6 eV, thanks to the bandgap engineering effect, and the emission color was simultaneously changed from green to yellow due to the variation of crystal field strength. Image information was recorded on the PiG films by using a 450 nm blue-light laser in a laser direct writing mode and the recorded information was retrieved under high-temperature thermal stimulation or photostimulation. The Y3Al5- xGa xO12:Ce3+,V3+ PiG films as presented in this work are very promising in the applications of multidimensional and rewritable optical information storage.

Long persistent and photo‐stimulated luminescence in Pr3+‐doped layered perovskite phosphor for optical data storage

AbstractAs the time for big data is coming, the demand for data's storage density and capacity exerts explosive growth. However, traditional optical storage is hard to get rid of the bottleneck of optical diffraction limit. The persistent luminescence materials could be used for optical data storage based on the photon trapping and de‐trapping mode. Herein the performance of thermoluminescence (TL), photo‐stimulated luminescence, and photoluminescence of Pr3+‐doped Ca4Ti3O10 were studied in order to explore the optical storage property of this material. The TL glow curves show that the deep‐trap in Ca4Ti3O10:0.01Pr3+, Y3+ has a narrow distribution from 0.9 to 0.98 eV, which is qualified for maintaining the recorded data at RT for a long duration time. NIR photo‐stimulated red persistent luminescence (NIR‐to‐red mode) as presented in the Y‐containing Ca4Ti3O10:Pr3+ phosphor could be a promising technique for optical data storage.

Investigation of the long afterglow mechanism in SrAl2O4:Eu2+/Dy3+ by optically stimulated luminescence and thermoluminescence

After the discovery of new-generation persistent luminescence materials based on Eu2+, there are many debates on their long-lasting mechanism. In this work, SrAl2O4:Eu2+/Dy3+ codoped and single doped samples were analyzed by optically stimulated luminescence and thermoluminescence to clarify the long afterglow mechanism involved. The phenomenon that persistent luminescence can be realized by the excitation of 475 nm laser in SrAl2O4:Eu2+, Dy3+ evidenced that the energy of Dy3+ can transfer to Eu2+ eventually in SrAl2O4:Eu2+, Dy3+. And the optically stimulated luminescence under the excitation of 980 nm both in SrAl2O4:Eu2+, Dy3+ and SrAl2O4:Eu2+ indicated that the electron traps caused by oxygen vacancies were significant for the long-lasting luminescence. The distribution of trap depth was precisely discussed as well by analyzing a series of thermoluminescence results with varying excitation temperature, and it showed the dysprosium doping introduced a shallow trap type with depth less than 0.65 eV. This work presents a clear view of the mechanism of the persistent luminescence in SrAl2O4:Eu2+, Dy3+, and could be generalized to the other analogous long afterglow materials based on Eu2+.

Gaussian approximation of thermoluminescence (TL) peaks: A common misconception for analysis of TL of persistent luminescent materials

Whenever one over simplifies a physical phenomenon or even any concept, misconceptions are bound to occur. This seems to be true in the case of use of thermoluminescence (TL) in the study of materials by non-specialists. The fact that most semiconducting/insulating materials exhibit TL has led to many publications that ignore the basic rules of use of TL in determining the two key intrinsic trapping parameters, the trap-depth (E) and the frequency factor (s) that control the phenomenon. Manipulation of the value of E and s in a system by suitable activator and co-activator leads to the optimization for specific use of materials. In this work we discuss a common misconception that has been continuously propagated. It is the deconvolution of complex glow curves using Gaussian function and using the component of TL peaks to calculate trap depth (E) by peak shape method. This assumption is questionable and can yield parameters that are physically unrealistic. To prove our point, we consider as many as four phosphors namely ZnS:Cu+ Co2+, CaxSr1-xS:Eu, Sr2MgSi2O7;Eu2+Dy3+ and BaZrSi3O9:Eu2+.

Near-infrared rechargeable “optical battery” implant for irradiation-free photodynamic therapy

As a minimal or noninvasive therapeutic method for tumors, photodynamic therapy (PDT) induced by the external laser irradiations has attracted great attentions. However, the UV–visible responsive property with low tissue penetration and photothermal effect from the prolonged irradiation impedes their further applications. Herein, a near-infrared (NIR) rechargeable “optical battery” for irradiation-free PDT is fabricated by embedding upconversion materials, persistent luminescence materials, photosensitizer into biocompatible polydimethylsiloxane. After 5 s quickly charged by 980-nm NIR laser, the PDT “optical battery” can generate green persistent luminescence and produce cytotoxic singlet oxygen for continuous irradiation-free PDT (∼30 min) without external irradiation. Due to deep tissue penetration and discontinuous short exposure of NIR light charging source, the “optical battery” can still be charged to continuously generate singlet oxygen in deep tissue (∼4 mm) with low photothermal effect. The PDT implant can be easily optimized in size and shape aiming at different nidus sites and achieved different functions by adding other functional components (e.g. CaO2 for oxygen envolving to overcome hypoxia tumor). The effective tumor proliferation inhibiting capability of this NIR rechargeable “optical battery” may give rise to next generation of intelligent stimuli-responsive nanomedicine and noninvasive photo bio-stimulation research for future clinical applications.

The World Needs New Colors: Cutting Edge Mobility Focusing on Long Persistent Luminescence Materials

AbstractThe front cover artwork is provided by the authors and the Karlsruhe Institute of Technology (KIT; Germany). This article highlights how long persistent luminescent materials may be used as road markings to illuminate the route ahead for vehicles, such as the autonomous research car of the KIT shown in the cover image. Read the full text of the Minireview at 10.1002/cptc.201700215.

The World Needs New Colors: Cutting Edge Mobility Focusing on Long Persistent Luminescence Materials

AbstractThe increasing number of “self‐driving vehicles” produced by the automotive and non‐automotive industries and the increased use of driver assistance systems requires ultimately an adaption of appropriate road markings. For this purpose, carefully designed near‐infrared (NIR) and short‐wave infrared (SWIR) emitters will play an emerging role in the future. Correspondingly this Minireview will present new trends for the application of long persistent luminescence materials for future developments in the field of NIR and SWIR emitters, respectively.

Trap Depth Engineering of SrSi2O2N2:Ln2+,Ln3+ (Ln2+ = Yb, Eu; Ln3+ = Dy, Ho, Er) Persistent Luminescence Materials for Information Storage Applications.

Deep-trap persistent luminescence materials exhibit unique properties of energy storage and controllable photon release under additional stimulation, allowing for both wavelength and intensity multiplexing to realize high-capacity storage in the next-generation information storage system. However, the lack of suitable persistent luminescence materials with deep traps is the bottleneck of such storage technologies. In this study, we successfully developed a series of novel deep-trap persistent luminescence materials in the Ln2+/Ln3+-doped SrSi2O2N2 system (Ln2+ = Yb, Eu; Ln3+ = Dy, Ho, Er) by applying the strategy of trap depth engineering. Interestingly, the trap depth can be tailored by selecting different codopants, and it monotonically increases from 0.90 to 1.18 eV in the order of Er, Ho, and Dy. This is well explained by the energy levels indicated in the host-referred binding energy scheme. The orange-red-emitting SrSi2O2N2:Yb,Dy and green-emitting SrSi2O2N2:Eu,Dy phosphors are demonstrated to be good candidates of information storage materials, which are attributed to their deep traps, narrow thermoluminescence glow bands, high emission efficiency, and excellent chemical stability. This work not only validates the suitability of deep-trap persistent luminescence materials in the information storage applications, but also broadens the avenue to explore such kinds of new materials for applications in anticounterfeiting and advanced displays.

Photocatalysis in Darkness: Optimization of Sol-Gel Synthesis of NP-TiO2 Supported on a Persistent Luminescence Material and its Application for the Removal of Ofloxacin from Water

In the present work, a new photocatalyst based on a new persistent luminescence phosphor, PeLM, and NPs- TiO2 was synthesized and the synthesis was optimized using a chemometric approach. A solid-state synthesis was used to obtain the persistent luminescence material while a sol-gel synthesis was used to obtain anatase NPs-TiO2. Each sample was then characterized by means of XRD, SEM and BET analysis, while the photocatalytic activity was evaluated testing the percent degradation of a methylene blue aqueous solution. Two different kinds of experiments were performed on the optimized sample, using a continuous irradiation or halving it with darkness cycles. It’s been demonstrated that the PeLM acts as an internal source for TiO2, providing the excitation required for the photocatalysis and so allowing to continue photon absorption even in darkness conditions. The two materials were coupled by means of a solid-state synthesis, varying the ratio between the reagents (1, 6), the heating temperature (350, 550°C) and time (1, 6 hours) through a chemometric approach, in order to find the optimized values. Validating the model led to the conclusion that the parameters affecting the synthesis have no significant interactions among them. The obtained results demonstrated the real applicability of this coupled system in the removal of Ofloxacin from water solution as probe of emerging organic pollutants.

Unveiling the role of the hexagonal polymorph on SrAl2O4-based phosphors.

In persistent luminescence materials, the SrO–Al2O3 system has been mainly studied due to its chemical stability, higher photoluminescence response and longest green-afterglow times. Specifically, the research has focused on SrAl2O4 doped with europium and dysprosium. SrAl2O4 has two polymorphs: monoclinic polymorph (space group P21) and hexagonal polymorph (space group P6322). Besides, the coexistence of these two phases, monoclinic and hexagonal, appears in almost all the results. However, it is not clear how this coexistence influences optical response. Some authors have reported that only the monoclinic structure exhibits luminescence properties, while another suggests that the hexagonal SrAl2O4 polymorph has a higher emission efficiency than the monoclinic polymorph. Here we report a systematic evaluation of the effects of the stabilization of the hexagonal SrAl2O4 polymorph. We show that an interrelationship between the hexagonal polymorph and phosphorescent properties is the linchpin for the development of good luminescence properties. Remarkably, the stabilization of the hexagonal SrAl2O4 polymorph on the monoclinic–hexagonal polymorphic coexistence appears to be related to the preservation of the nanometric nature of the SrAl2O4-based system. Our results will help to understand the role of the hexagonal polymorph in the polymorphic coexistence on SrAl2O4-based systems and may facilitate the development of luminescent nanometric particles for the design and preparation of new light emitting materials.

Persistent luminescence warm-light LEDs based on Ti-doped RE2O2S materials prepared by rapid and energy-saving microwave-assisted synthesis

Persistent luminescence materials based on Ti-doped rare earth oxysulfides were obtained by a rapid, one-step process for application in self-sustained warm-light LEDs.