Search Results (23)

Achieving long-lived room-temperature phosphorescence (RTP) with high quantum efficiency is of significant interest for applications in anti-counterfeiting, flexible optoelectronic displays, and multi-level information encryption. Here, we presented a hydrogen-bond engineering strategy to enhance RTP performance by progressively increasing the number of hydrogen-bonding sites within a polyvinyl alcohol (PVA) matrix. A series of carbazole-based chromophores (Cz, ICz and 2ICz) were embedded into the PVA network, and their photophysical properties were systematically characterized using steady-state photoluminescence spectra, time-decay spectra, Fourier-transform infrared (FTIR), and Raman and X-ray photoelectron spectroscopy (XPS). Spectroscopic analysis revealed that the increased number of N-H groups significantly strengthened hydrogen-bonding interactions, effectively suppressing non-radiative decay pathways and stabilizing triplet excitons. As a result, the phosphorescence lifetime was prolonged up to 1.68 s with a quantum yield of 38.63%. Furthermore, leveraging the spectral overlap integral between the phosphorescent emission and dye absorption, efficient Förster resonance energy transfer (FRET) was realized, enabling tunable multi-color afterglow emissions. This study establishes a design strategy validated by spectroscopy for high-performance RTP materials and highlights their promising potential in advanced optical encryption and flexible photonic applications. Full article

A novel long-lasting luminescent composite material based on the (Ca,Sr)-Al-O system was synthesized using a solution combustion method. (Ca,Sr)₃Al₂O₆ is the primary phase, with SrAl₂O₄ as a controllable secondary phase. Compared to conventional single-phase SrAl₂O₄ phosphors, the introduction of a calcium-rich hexaaluminate matrix creates additional defects and a specific trap distribution at the composite interface, significantly improving carrier storage and release efficiency. Eu²⁺ + Nd³⁺ synergistic doping enables precise control of the trap depth and number. Under 365 nm excitation, Eu²⁺ emission is located at ~515 nm, with Nd³⁺ acting as an effective trap center. Under optimal firing conditions at 700 °C (Eu²⁺ = 0.02, Nd³⁺ = 0.003), the afterglow lifetime exceeds 30 s. Furthermore, The (Ca,Sr)₃Al₂O₆ host stabilizes the lattice and optimizes defect states, while synergizing with the SrAl₂O₄ secondary phase to improve the afterglow performance. This composite phosphor exhibits excellent dual-mode anti-counterfeiting properties: long-lasting green emission under 365 nm excitation and transient blue-violet emission under 254 nm excitation. Based on this, a screen-printing ink was prepared using the phosphor and ethanol + PVB, enabling high-resolution QR code printing. Pattern recognition and code verification can be performed both in the UV on and off states, demonstrating its great potential in high-security anti-counterfeiting applications. Compared to traditional single-phase SrAl₂O₄ systems, this study for the first time constructed a composite trap engineering of the (Ca,Sr)₃Al₂O₆ primary phase and the SrAl₂O₄ secondary phase, achieving the integration of dual-mode anti-counterfeiting functionality with a high-resolution QR code fluorescent ink. Full article

Host/guest doping is an effective approach to achieving room-temperature phosphorescence (RTP). However, the influence of the host matrix on doping systems is still unclear, and it is difficult to select the suitable host species for a certain guest emitter. This study prepared a series of host/guest RTP materials with dynamically adjustable time and color by doping a non-RTP guest material in various host materials that were easy to crystallize. The varying afterglow color originated from the difference in Förster energy transfer between the host and guest. Specifically, the change from yellow to green afterglow was realized by varying the host’s molecular structure. This study further revealed the importance of proper host energy levels, the ability to generate long-aging triplet excitons, and the Förster energy transfer from host to guest. Additionally, multiple information encryption anti-counterfeiting materials were developed by leveraging the different afterglow colors and durations, reflecting the unique performance advantages of the prepared long-afterglow materials in various RTP applications. Full article

Solution-processable hole-transporting materials (HTMs) that form highly soluble films and thermally stable amorphous states are essential for advancing optoelectronic devices. However, the currently commercialized HTM, N,N-bis(3-methylphenyl)-N,N0-bis(phenyl)benzidine (TPD), exhibits poor solubility and limited carrier transport when spin-coated into thin films. Herein, to address these issues, a fluorenyl group was ingeniously incorporated into a series of molecules structurally similar to TPD. The resulting compounds, namely, 2,7-di-(N,N-diphenylamino)-9,9-dimethyl-9H-fluorene (DDF), 2,7-di-p-tolyl-(N,N-diphenylamino)-9,9-dimethyl-9H-fluorene (2M-DDF), and 2,7-di-tetra-p-tolyl-(N,N-diphenylamino)-9,9-dimethyl-9H-fluorene (4M-DDF), offered tunable energy levels, carrier transport, crystallinity, and steric configuration via adjustment of the number of terminal methyl groups. Owing to its satisfactory performance, 2M-DDF can serve as an effective alternative to TPD in OLED devices as well as a guest molecule in host–guest systems for long-afterglow materials. Devices incorporating 2M-DDF as the HTM, with an Alq₃ emitter, achieved a maximum CE of 4.78 cd/A and a maximum L (L_max) of 21,412 cd m⁻², with a turn-on voltage (V_on) of 3.8 V. The luminous efficiency of 2M-DDF was approximately five times that of TPD (4106 cd m⁻²). Furthermore, when 2M-DDF and TPD were utilized as guest molecules in afterglow materials, the afterglow duration of 2M-DDF (10 s) was 2.5 times that of TPD (4 s). This study provides a theoretical basis for the development of high-performance HTMs and long-afterglow materials, establishing a framework for the application of fluorene-based compounds in emerging fields such as long-afterglow materials. Full article

The measurement and description of the charge-carrier lifetime (${\tau }_{\mathrm{c}}$) is crucial for the wide-ranging applications of lead-halide perovskites. We present time-resolved microwave-detected photoconductivity decay (TRMCD) measurements and a detailed analysis of the possible recombination mechanisms including trap-assisted, radiative, and Auger recombination. We prove that performing injection-dependent measurement is crucial in identifying the recombination mechanism. We present temperature and injection level dependent measurements in CsPbBr₃, which is the most common inorganic lead-halide perovskite. In this material, we observe the dominance of charge-carrier trapping, which results in ultra-long charge-carrier lifetimes. Although charge trapping can limit the effectiveness of materials in photovoltaic applications, it also offers significant advantages for various alternative uses, including delayed and persistent photodetection, charge-trap memory, afterglow light-emitting diodes, quantum information storage, and photocatalytic activity. Full article

Due to their low cost, good biocompatibility, and ease of structural modification, organic long-persistent luminescence (LPL) materials have garnered significant attention in organic light-emitting diodes, biological imaging, information encryption, and chemical sensing. Efficient charge separation and carrier migration by the host–guest structure or using polymers and crystal to build rigid environments are effective ways of preparing high-performance materials with long-lasting afterglow. In this study, four types of crystalline materials (MODPA: DDF-O, MODPA: DDF-CHO, MODPA: DDF-Br, and MODPA: DDF-TRC) were prepared by a convenient host–guest doping method at room temperature under ambient conditions, i.e., in the presence of oxygen. The first three types exhibited long-lived charge-separated (CS) states and achieved visible LPL emissions with durations over 7, 4, and 2 s, respectively. More surprisingly, for the DDF-O material prepared with PMMA as the polymer substrate, the afterglow time of DDF-O: PMMA was longer than 10 s. The persistent room-temperature phosphorescence effect caused by different CS state generation efficiencies and rigid environment were the main reason for the difference in LPL duration. The fourth crystalline material was without charge separation and exhibited no LPL because it was not a D-A system. The research results indicate that the CS state generation efficiency and a rigid environment are the key factors affecting the LPL properties. This work provides new understandings in designing organic LPL materials. Full article

This manuscript describes the synthesis of green long afterglow nanophosphors SrAl₂O₄:Eu²⁺, Nd³⁺ using the combustion process. The study encompassed the photoluminescence behavior, elemental composition, chemical valence, morphology, and phase purity of SrAl₂O₄:Eu²⁺, Nd³⁺ nanoparticles. The results demonstrate that after introducing Eu²⁺ into the matrix lattice, it exhibits an emission band centered at 508 nm when excited by 365 nm ultraviolet light, which is induced by the 4f⁶5d¹→4f⁷ transition of Eu²⁺ ions. The optimal doping concentrations of Eu²⁺ and Nd³⁺ were determined to be 2% and 1%, respectively. Based on X-ray diffraction (XRD) analysis, we have found that the physical phase was not altered by the doping of Eu²⁺ and Nd³⁺. Then, we analyzed and compared the quantum yield, fluorescence lifetime, and afterglow decay time of the samples; the co-doped ion Nd³⁺ itself does not emit light, but it can serve as an electron trap center to collect a portion of the electrons produced by the excitation of Eu²⁺, which gradually returns to the ground state after the excitation stops, generating an afterglow luminescence of about 15 s. The quantum yields of SrAl₂O₄:Eu²⁺ and SrAl₂O₄:Eu²⁺, Nd³⁺ phosphors were 41.59% and 10.10% and the fluorescence lifetimes were 404 ns and 76 ns, respectively. In addition, the E_g value of 4.98 eV was determined based on the diffuse reflectance spectra of the material, which closely matches the calculated bandgap value of SrAl₂O₄. The material can be combined with polyacrylic acid to create optical anti-counterfeiting ink, and the butterfly and ladybug patterns were effectively printed through screen printing; this demonstrates the potential use of phosphor in the realm of anti-counterfeiting printing. Full article

This paper reviews the research progress and development of aluminate long afterglow luminescent materials in the field of road marking, especially the study of rare earth ion-activated strontium aluminate (SrAl₂O₄: Eu²⁺, Dy³⁺)-based long afterglow powders. This article begins by describing the importance of road markings and the need to improve their visibility and durability at night and in adverse weather conditions. Subsequently, the current passive and active methods for improving the visibility of marking materials are discussed in detail, focusing on the advantages of aluminate long afterglow materials and challenges related to their hydrolysis and thermal stability. Through the application of organic–inorganic composite coating technology, the water resistance and thermal stability of the materials can be improved, thus enhancing the performance of road markings. This article also summarizes the current research status of different types of long afterglow road marking coatings. It analyzes the luminescence mechanism of aluminate long afterglow materials. Additionally, this article discusses future research directions and application prospects. The aim is to provide technical references and support for the wide application of long afterglow self-luminous road marking coatings. Full article

Long-afterglow materials have a broad of applications in optoelectronic devices, sensors, medicine and other fields due to their excellent luminescent properties. The host-guest long-afterglow MOFs material combines the advantages of multi-component characteristics and the stability of MOFs, which improves its luminous performance and expands its other properties. This review introduces the classification, synthesis and application of host-guest MOFs materials with long afterglow. Due to their rigid frames and multi-channel characteristics, MOFs can load common guest materials including rare earth metals, organic dyes, carbon dots, etc. The synthesis methods of loading guest materials into MOFs include solvothermal synthesis, post-encapsulation, post-modification, etc. Those long-afterglow host-guest MOFs have a wide range of applications in the fields of sensors, information security and biological imaging. Full article

This study examines the use of SrAl₂O₄: Eu²⁺, Dy³⁺ long-afterglow materials doped into g-C₃N₄/TiO₂ coatings for photodegradation. The prepared sample was tested for the purification of automotive exhaust fumes, with the optimal mass ratio of g-C₃N₄/TiO₂ and SrAl₂O₄: Eu²⁺, Dy³⁺ determined to be 1:1. Characterization tests, including XRD, FT-IR, XPS, and TG-DSC, were conducted to evaluate the microstructure and properties of the samples. Under poor lighting conditions, g-C₃N₄/TiO₂ reduced CH and NO_x by 59 ppm and 13 ppm within 4 h, respectively, while g-C₃N₄/TiO₂/SrAl₂O₄: Eu²⁺, Dy³⁺ decreased CH and NO_x by 98ppm and 34ppm, respectively, resulting in a significant improvement in degradation efficiency. The addition of long-afterglow materials significantly improves the efficiency of photocatalysts in purifying exhaust fumes in low-light environments, providing potential value for all-weather exhaust treatment in the future. Full article

Narrowband afterglow materials display interesting functions in high-quality anti-counterfeiting and multiplexed bioimaging. However, there is still a limited exploration of these afterglow materials, especially for those with a full width at half maxima (FWHM) around 30 nm. Here, we report the fabrication of narrowband organic/inorganic hybrid afterglow materials via energy transfer technology. Coronene (Cor) with a long phosphorescence feature and broad phosphorescence band is selected as the donor for energy transfer, and inorganic quantum dots (QDs) of CdSe/ZnS with a narrowband emission are used as acceptors. Upon doping into the organic matrix, the resultant three-component materials exhibit a narrowband afterglow with an afterglow lifetime of approximately 3.4 s and an FWHM of 31 nm. The afterglow wavelength of the afterglow materials can be controlled by the QDs. This work based on organic/inorganic hybrids provides a facile approach for developing multicolor and narrowband afterglow materials, as well as opens a new way for expanding the features of organic afterglow for multifunctional applications. It is expected to rely on narrowband afterglow emitters to solve the “spectrum congestion” problem of high-density information storage in optical anti-counterfeiting and information encryption. Full article

Preparing submicron and nanoscale phosphors with good optical properties for practical applications is a challenging task for current inorganic long afterglow luminescent materials. This study utilized commercialized SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors (SAOED) as raw materials and employed solvents with lower polarity or non-polar solvents for dynamic solvothermal treatment. The commercialized phosphor’s overall average particle size was reduced from 42.3 μm to 23.6 μm while maintaining the fluorescence intensity at 91.39% of the original sample. Additionally, the study demonstrated the applicability of the dynamic solvothermal method to most other commercialized inorganic phosphors. The experiment produced a high-brightness nano-sized phosphor with a yield of 5.64%. The average diameter of the phosphor was 85 nm, with an average thickness of 16 nm. The quantum efficiency of the phosphor was 74.46% of the original sample. The fingerprint imaging results suggest that the nano-sized phosphors have potential for practical applications. Full article

A series of long-afterglow luminescent materials (SrAl₂O₄: Eu²⁺ (SAOE), SrAl₂O₄: Eu²⁺, Dy³⁺ (SAOED) and SrAl₂O₄: Eu²⁺, Dy³⁺, Gd³⁺ (SAOEDG)) was synthesized via the combustion method. Temperature and concentration control experiments were conducted on these materials to determine the optimal reaction temperature and ion doping concentration for each sample. The crystal structure and luminescent properties were analyzed via X-ray diffraction (XRD), photoluminescence (PL), and afterglow attenuation curves. The outcomes demonstrate that the kind of crystal structure and the location of the emission peak were unaffected by the addition of ions. The addition of Eu²⁺ to the matrix’s lattice caused a broad green emission with a central wavelength of 508 nm, which was attributed to the characteristic 4f⁶5d¹ to 4f⁷ electronic dipole, which allowed the transition of Eu²⁺ ions. While acting as sensitizers, Dy³⁺ and Gd³⁺ could produce holes to create a trap energy level, which served as an electron trap center to catch some of the electrons produced by the excitation of Eu²⁺ but did not itself emit light. After excitation ceased, this allowed them to gently transition to the ground state to produce long-afterglow luminescence. It was observed that with the addition of sensitizer ions, the luminous intensity of the sample increased, and the afterglow duration lengthened. The elemental structure and valence states of the doped ions were determined with an X-ray photoelectron spectrometer (XPS). Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to characterize the samples. The results show that the sample was synthesized successfully, and the type and content of ions in the fluorescent powder could be determined. The fluorescence lifetime, quantum yield, bandgap value, afterglow decay time, and coordinate position in the coherent infrared energy (CIE) diagram of the three best sample groups were then analyzed and compared. Combining the prepared phosphor with ink provides a new idea and method for the field of anti-counterfeiting through screen printing. Full article

With the whole society’s demand for intelligence, the smart highway has become the inevitable trend of road development. Luminescent road marking made of long persistent luminescent coating is a new type of functional marking that is designed with long afterglow luminescent material as the raw material and has many features such as safety, beauty and energy saving. Here, SrA1₂O₄:Eu²⁺,Dy³⁺ green long afterglow phosphors were prepared using a high-temperature solid state method. The green phosphors obtained at 1350 °C have two traps with a shallow trap depth of 0.66 eV and a deep trap depth of 0.8 eV. The green afterglow can be seen in the dark for more than 8 h after sunlight excitation for 2 h. The green long persistent luminescent coatings were synthesized using the blending method. The uniformity of each component can be improved by adding 1.25% SiO₂ into the luminescent coatings. The addition of 3.5% CaCO₃ will improve the compactness of the coatings and reduce water absorption. After soaking in water for 120 h, the afterglow intensity of the coating decreases to 76% of the original, showing good water resistance. After daylight excitation in different weather conditions (cloudy, sunny, rainy), the afterglow can reach more than 5 h; therefore, it can be applied to a smart highway. Full article

In this study, we utilized a simple and efficient microwave heating method with polyethyleneimine (PEI) and phosphate as raw materials to synthesize room temperature persistent luminescence (RTPL) materials that emit phosphorescent light for up to 10 s. Our investigation revealed that the optimal synthesis conditions were a microwave radiation power of 560 W and a heating time of 5 min. The synthesized RTPL materials had an average particle size of 2 nm and exhibited excellent RTPL performance, with optimal excitation and emission wavelengths of 360 nm and 544 nm, respectively. Additionally, these materials displayed good water solubility. We conducted mapping experiments and in situ phosphorescent imaging of plants to showcase the potential applications of RTPL materials in the fields of biological imaging and anti-counterfeiting. Overall, our findings demonstrate the promising potential of these RTPL materials as versatile tools for various practical applications. Full article