Carbon nanotube (CNT) cathode materials exhibit excellent electron emission performance and have become a key research focus in the field of vacuum electronics. However, their practical applications are still restricted by challenges, including emission instability and ambiguity in temporal resolution capability. This work investigated the thermal-assisted field emission characteristics of CNT and their application in pulsed X-ray imaging. Systematic characterization of the turn-on field strength, emission stability, pulse response characteristics, and pulsed X-ray imaging performance demonstrated that the thermal-assisted operating mode reduced current fluctuations to below 1%. Increasing the heating power further enhanced emission stability and lowered the turn-on field strength. In thermal-assisted pulsed emission mode, CNT cathodes exhibited reduced power consumption compared to conventional thermionic cathodes and achieved microsecond-scale pulse response. Further X-ray imaging experiments confirmed that the X-ray dose generated by CNT in this operational mode exhibited higher stability, enabling 100 μs pulsed imaging and clear visualization of rotating blades operating at 600 Hz. This study validated the feasibility of CNT cathodes for high-speed X-ray imaging and could provide a reference for the development of advanced pulsed X-ray sources and related technologies.

PEDOT:PSS is one of the most widely used hole transport materials in tin-based perovskite solar cells. However, the acid residues in PEDOT:PSS cause chemical/physical reactions with the ITO electrode. In this study, we utilized [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) and [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid (Me-4PACz) as buffer layers between PEDOT:PSS and ITO. The charge carrier transport ability of the SAM/PEDOT:PSS layer was significantly improved compared to that of the pure PEDOT:PSS layer. With SAM/PEDOT:PSS as the bottom layer, the tin-based perovskite films showed an improved morphology, suppressed Sn2+/Sn4+ oxidation, and a prolonged carrier lifetime; meanwhile, the perovskite film showed a reduced defect density, especially deep-level defect densities. Consequently, the champion tin-based devices achieved an increase in PCE from 5.7% (control device) to 7.3% (Me-4PACz/PEDOT:PSS device), while also retaining 80% of the initial PCE after 750 hours of storage in a N2 environment.

Conventional metal-tip-based laser-driven electron sources are normally constrained by a trade-off between energy spread and pulse width due to optical-field-induced free electron acceleration. This makes it challenging to surpass the current state-of-the-art, which exhibits energy spreads exceeding 1 eV and pulse durations of hundreds of femtoseconds. Here we report an unconventional delayed emission from a one-dimensional carbon-nanotube-based electron source. By utilizing a special pump-probe approach, we apply 7-fs laser pulses to the carbon-nanotube emitters and observe free electron emission tens of femtoseconds after the pulse. This delayed emission results in a substantially reduced energy spread of approximately 0.3 eV and an electron pulse width of about 13 fs. Through time-dependent density functional theory calculations, we find that the delayed emission is driven by the interplay of collective oscillations and electron-electron interactions. Our results may provide a promising technology for developing cutting-edge ultrafast electron sources.

Solution combustion-synthesized BaAl2O4: Eu2+, Nd3+, and Pr3+ blue–green long-afterglow phosphors are prepared and systematically investigated. First, XRD confirms the BaAl2O4 host and screens for trace residual features. SEM reveals the agglomerated granular morphology typical of combustion products. XPS verifies the valence states (Eu2+, Nd3+, Pr3+) and the chemical environment of the host lattice. UV-Vis diffuse reflectance spectra, transformed via the Kubelka–Munk function and analyzed using Tauc plots (indirect-allowed), indicate a wide band gap of the BaAl2O4 host with small, systematic shifts upon Nd3+/Pr3+ co-doping. PL measurements show Eu2+ 4f–5d emission and co-dopant-assisted excitation/defect pathways without altering the Eu2+ emission band shape. Afterglow lifetime and decay analyses correlate trap depth/distribution with the extended persistence. Finally, we demonstrate anti-counterfeiting by (i) snowflake printing and (ii) a binary 3 × 3 grid printed with two afterglow inks of different lifetimes to realize multi-level authentication. The sequential evidence links structure, chemistry, optical absorption, carrier trapping, and practical readout, providing a coherent basis for performance enhancement and application.

Tin-based perovskite solar cells are a new type of photovoltaic technology. Tin-based perovskite solar cells use tin instead of traditional lead for the sake of environmental friendliness. Currently, the key challenges lie in solving the problems of low filling factor, low short-circuit current density, and low open-circuit voltage, which together lead to the overall performance decline in the cells. In this context, we conducted a detailed comparative analysis of the defect state passivation on the surface and interface of tin-based perovskite using phenethylammonium salts (PEAX, X = Cl, I, Br). The results show that doping PEAX in perovskite can improve the morphology, and hydrophobicity of the thin film. At the same time, the carrier recombination lifetime of the device modified by PEAX increases, and the carrier transport lifetime decreases. This indicates that the passivated device has a lower recombination rate and an increased charge transfer rate after illumination, thus reducing carrier recombination. In addition, the embedded electric field and composite resistance of the devices doped with PEAX are increased, and the density of defect states is decreased, which promotes carrier transfer, inhibits dark-state recombination, thereby improving the filling factor, short-circuit current density and open-circuit voltage of the device, and further improving the power conversion efficiency of the device. It is worth noting that among the three PEAX materials used for passivation, PEACl has the best passivation effect, and the highest efficiency of the device after PEACl passivation is 5.74 %. The study provides useful information on passivation methods for tin-based perovskite solar cells.

Tin-based perovskite represents a highly promising alternative to lead-based perovskite, offering a number of significant advantages. These include non-toxicity, high absorbance, and excellent photovoltaic properties. The use of the toxic anti-solvent chlorobenzene (CBZ) in the preparation of tin-based perovskite thin films has the dual disadvantage of increasing the environmental hazards and the cost of subsequent treatment. The use of acetic acid (HAc) as a green anti-solvent has been demonstrated to effectively regulate the crystallization process of tin-based perovskite FASnI3, resulting in the preparation of perovskite films of superior quality. To further enhance the performance of tin-based perovskite, Zhao et al., organic cation mixing was used to add MAI to the FASnI3 system and optimize the ratio, resulting in an optimal ratio of FA (0.75) MA (0.25) (FA = NH2CH = NH2+, MA = CH3NH3+) (Zhao et al. Adv Sci 4(11):1700204, 2024). In this study, we choose the crystallization process during the preparation of binary FA0.75MA0.25SnI3 perovskite using a green anti-solvent HAc. The findings demonstrated that HAc was capable of influencing the crystallization of binary tin-based perovskite, facilitating the formation of perovskite films with minimal pinholes and enhanced uniformity and crystallinity. Additionally, the resulting perovskite exhibits a band gap of 1.35 eV, which is in close alignment with the predicted ideal band gap as postulated by Schottky's theory. Furthermore, it displays enhanced hydrophobic properties. In the binary perovskite photovoltaic device prepared using the anti-solvent HAc, the maximum device efficiency reached 3.62

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.

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 Eg 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.

Tin-based perovskite has been considered as one of the most potential candidates for lead-based perovskite. The solution proceed method was widely utilized in fabricating tin perovskite solar cells. So far, all fabrication processes for tin perovskite solar cells involved toxic organic solvents, which is contrary to the development of environmentally friendly perovskite solar cells. In this study, we report for the first time, by using a mixed green solvent N-diethyl formamide and green 1,3-dimethyl-3,4,5,6-Tetrahydro-2 (1H)-pyrimidinone as precursor solvent, and a green solvent dibutyl ether as antisolvent, a high-quality FA0.75MA0.25SnI3 film was achieved. The optical band gap of the prepared perovskite layer was 1.36 eV, which was close to the ideal band gap. The green-solution-proceed perovskite films showed reduced defect density. As a consequence, the champion green-solution-proceed photovoltaic device achieved a power conversion efficiency of 4.4%. Moreover, it still maintains 80% of the initial efficiency after 600 h of storage in a nitrogen atmosphere. This work would promote the perovskite solar cells from a 'new' technique to a 'new and green' technique.

Field emission is an important work mode for electron sources, and carbon nanotubes (CNTs) have been extensively studied for their good emission properties. It is well known that the parameters of the grid deeply influence the field emission performance of CNTs, a relationship that requires further elucidation. Therefore, in this study, the relationship between the grid aperture ratio and electron transmittance was studied through simulations and experiments. This study’s results indicate that the electron transmittance improved as the grid aperture ratio increased. Meanwhile, electron beam spot simulations and imaging experiments indicate that an increased grid aperture ratio will expand the cathode electron divergence, leading to a larger electron beam spot size. These results demonstrate that there is a trade-off in maintaining the grid aperture ratio between high electron transmittance and relatively small electron beam spot size, and the optimum grid aperture ratio is between 75% and 85%. These results will provide a reference for the design and optimization of X-ray tubes and other electron sources.

Herein, a series of novel long afterglow nanophosphors BaYAl3O7:Eu2+, Nd3+ was synthesized by the combustion method. The investigation encompassed the characterization of X-ray diffraction, morphology, chemical valence, elemental composition, and photoluminescence behavior of BaYAl3O7:Eu2+ and BaYAl3O7:Eu2+, Nd3+ nanoparticles. Under 365 nm excitation, BaYAl3O7:Eu2+ and BaYAl3O7:Eu2+, Nd3+ show emission bands centered at 497 nm and 492 nm, which are attributed to the 4f65d→4f7 transition of Eu2+ ions. The optimal samples of BaYAl3O7:0.03Eu2+ and BaYAl3O7:0.03Eu2+, 0.02Nd3+ have average fluorescence lifetimes of 850 ns and 1149 ns, respectively. The co-doping of Nd3+ ions as the trap centers produced long afterglow luminescence properties, and the afterglow time could reach up to 8 min. Furthermore, the fluorescent powder can be mixed with polyacrylic acid to prepare anti-counterfeiting inks; a clover pattern and snowflake pattern have been successfully printed using screen printing technology, proving its potential application in the field of anti-counterfeiting.

Herein, a series of Ba0.5Sr0.5Al2O4: xEu2+ (x = 0.01, 0.02, 0.03, 0.04, 0.06) nanophosphors were synthesized by a combustion method. The investigation encompassed the characterization of the phase purity, morphology, elemental composition, and photoluminescence behavior of Ba0.5Sr0.5Al2O4: xEu2+ nanoparticles. Under excitation by 303 nm and 365 nm ultraviolet light, the nanoparticles exhibited blue-green emission arising from the 4f65d→4f7 transition of Eu2+ ions. The optimal doping concentration was determined to be 2%. Notably, the nanoparticles demonstrated fluorescence lifetimes and quantum yields of 1010 ns (λex = 303 nm), 112 ns (λex = 365 nm), 10.5%, and 10.3%, respectively. Additionally, a comprehensive analysis of the band structure and electronic density of states was conducted, revealing a theoretical direct band gap of 4.05 eV for the Ba0.5Sr0.5Al2O4 host. In addition, the prepared fluorescent powder can be used to prepare fluorescent flexible films. This film does not change the characteristic emission of Eu2+ ions and has more stable physicochemical properties, which may be more suitable for use in harsh environments. Also, the fluorescent powder can be blended with polyacrylic acid to form colorless anti-counterfeiting ink that can be applied to banknotes as an anti-counterfeiting mark. A clover pattern was successfully printed using screen-printing technology, proving its potential application in the field of anti-counterfeiting.

Green emitting long afterglow phosphor SrAl2O4: Eu2+, Dy3+ was synthesized via the combustion method. The physical phase analysis was carried out by X-ray diffraction, the results show that the introduction of Eu2+ into the lattice of the matrix resulted in a broad green emission centered at 508 nm, which is ascribed to the characteristic 4f(6)5d(1) to 4f(7) electronic dipole allowed transition of Eu2+ ions. The doping of Eu2+ and Dy3+ did not change the physical phase of the crystals. Dy3+, as a coactivator, does not emit light itself, but can generate holes to form a trap energy level, which acts as an electron trap center to capture some of the electrons generated by the excitation of Eu2+. After excitation has ceased, let them gradually to transfer to the ground state for long afterglow luminescence. Then, we investigate the optical characterizations of different samples excited by X-ray. We found that SrAl2O4: Eu2+, 0.5% Dy3+ has this higher luminous intensity and afterglow. Its fluorescence lifetime is about 720 ns, and its quantum yield can reach 15.18%. Through search engine marketing (SEM) and energy dispersive X-ray spectroscopy (EDX), it has been proved that the sample has been successfully synthesized and its component content has been confirmed. The Eg value calculated from the diffuse reflectance spectrum is 4.61eV. The prepared SrAl2O4: Eu2+, Dy3+ luminescent powder is combined with Polydimethylsiloxane substrate for anticounterfeiting application, which provides a novel idea and method for the development of the anticounterfeiting field.

A single‐electron emitter, based on a single quantized energy level, can potentially achieve ultimate temporal and spatial coherence with a large emission current, which is desirable for atomic‐resolution electron probes. This is first developed by constructing a nano‐object on a metal tip to form a quantized double barrier structure. However, the single‐electron‐emission current can only achieve a picoampere level due to the low electron tunneling rate of the heterojunction with large barrier width, which limits the practical applications. In this study, carbon nanotubes (CNTs) serve as a single‐electron emitter and a current up to 1.5 nA is demonstrated. The double barrier structure formed on the CNT tip enables a high tunneling rate (≈10 12 s −1 ) due to the smaller barrier width. The emitter also shows high temporal coherence (energy dispersion of ≈10 meV) and spatial coherence (effective source radius of ≈0.85 nm). This work represents a highly coherent electron source to simplify the electron optics system of atomic‐resolution electron microscopy and sub‐10 nm electron beam lithography.

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 4f(6)5d(1) to 4f(7) 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.

Correction for ‘Enhanced field emission stability of vertically aligned carbon nanotubes through anchoring for X-ray imaging applications’ by Xinchuan Liu et al., J. Mater. Chem. C, 2023, 11, 2505–2513, https://doi.org/10.1039/d2tc04363g.

Carbon nanotubes (CNTs) show significant advantages in the development of cold cathode X-ray tubes due to their excellent field emission performance; however, there are still some problems, such as short lifetime and the low emission current of large-area CNTs. In this paper, a front-grid carbon nanotube array model was established, and the electric field intensity near the tip of the CNTs' electric field enhancement factor was analytically calculated. A simulation model of a CNT three-dimensional field emission electron gun was established by using computer simulation technology (CST). The effects of grid wire diameter, grid aperture shape, and the distribution of grid projection on the cathode surface on the cathode current, anode current, and electron transmission efficiency were analyzed. The aperture ratio was used to evaluate the grid performance, and the simulation results show that the ideal aperture ratio should be between 65% and 85%. A grid structure combining a coarse grid and a fine grid was designed, which can make the electric field intensity around the grid evenly distributed, and effectively increased the cathode emission current by 24.2% compared with the structure without the fine grid. The effect of grid aperture ratio on the electron transmission efficiency was tested. The simulation results and optimized structure can provide a reference for the grid design of cold cathode emission X-ray tubes.

We reported the anchored carbon nanotube emitters shows enhanced field emission stability.

Femtosecond laser–driven photoemission source provides an unprecedented femtosecond-resolved electron probe not only for atomic-scale ultrafast characterization but also for free-electron radiation sources. However, for conventional metallic electron source, intense lasers may induce a considerable broadening of emitting energy level, which results in large energy spread (>600 milli–electron volts) and thus limits the spatiotemporal resolution of electron probe. Here, we demonstrate the coherent ultrafast photoemission from a single quantized energy level of a carbon nanotube. Its one-dimensional body can provide a sharp quantized electronic excited state, while its zero-dimensional tip can provide a quantized energy level act as a narrow photoemission channel. Coherent resonant tunneling electron emission is evidenced by a negative differential resistance effect and a field-driven Stark splitting effect. The estimated energy spread is ~57 milli–electron volts, which suggests that the proposed carbon nanotube electron source may promote electron probe simultaneously with subangstrom spatial resolution and femtosecond temporal resolution.