Enhanced Storage Capacity via Anion Substitution for Advanced Delayed X-ray Detection.

X-ray radiation information storage, characterized by its ability to detect radiation with delayed readings, shows great promise in enabling reliable and readily accessible X-ray imaging and dosimetry in situations where conventional detectors may not be feasible. However, the lack of specific strategies to enhance the memory capability dramatically hampers its further development. Here, we present an effective anion substitution strategy to enhance the storage capability of NaLuF4:Tb3+ nanocrystals attributed to the increased concentration of trapping centers under X-ray irradiation. The stored radiation information can be read out as optical brightness via thermal, 980 nm laser, or mechanical stimulation, avoiding real-time measurement under ionizing radiation. Moreover, the radiation information can be maintained for more than 13 days, and the imaging resolution reaches 14.3 lp mm-1. These results demonstrate that anion substitution methods can effectively achieve high storage capability and broaden the application scope of X-ray information storage.

Strategy of Charge Compensation for High-Performance Ni2+-Activated MgAl2O4 Spinel Near-Infrared Phosphor Synthesis via the Sol-Gel Combustion Method.

Near-infrared (NIR) phosphor conversion light-emitting diodes (pc-LEDs) have great application potential as NIR light sources in many fields such as food analysis, night vision illumination, and bioimaging for noninvasive medical diagnosis. In general, phosphors synthesized by a high-temperature solid-phase method have large particle sizes and have to be processed to fine powders by a grinding process, which may introduce surface defects and lower the luminous efficiency. Here, we report a sol-gel sintering method with ammonium nitrate and citric acid as the sacrificing agents to synthesize high purity, nanosized (less than 50 nm) Zr4+/Ni2+ codoped MgAl2O4 spinel NIR phosphors, in which MgAl2O4 spinel is the matrix, Ni2+ is the luminous center, and Zr4+ acts as the charge compensator. We systematically characterized the crystal structures and NIR luminescence properties of the Ni2+-doped MgAl2O4 and the Zr4+/Ni2+ codoped MgAl2O4. Under 390 nm light excitation, the emission spectrum of the Ni2+-doped MgAl2O4 phosphor covers 900-1600 nm, the half-peak width is 251 nm, and the peak position is located at 1230 nm. We demonstrated that by incorporating small amounts of Zr4+ as the charge compensator, the NIR emission intensity of the Zr4+/Ni2+ codoped MgAl2O4 nanosized phosphor was doubled over that of the Ni2+-doped MgAl2O4 phosphor. The optimal content of the charge compensator was 2 mol %. More importantly, the inclusion of Zr4+ led to a NIR phosphor with improved thermal stability in luminous properties, and the luminous intensity measured at 100 °C was 33.83% of that measured at room temperature (20 °C). This study demonstrates that NIR phosphor nanomaterials with high-purity and enhanced optical properties can be designed and synthesized through the charge compensation strategy by a sol-gel sintering method.

Visualized X-ray Dosimetry for Multienvironment Applications.

X-ray dose detection plays a critical role in various scientific fields, including chemistry, materials, and medicine. However, the current materials used for this purpose face challenges in both immediate and delayed radiation detections. Here, we present a visual X-ray dosimetry method for multienvironment applications, utilizing NaLuF4 nanocrystals (NCs) that undergo a color change from green to red upon X-ray irradiation. By adjustment of the concentrations of Ho3+, the emission color of the NCs can be tuned thanks to the cross-relaxation effects. Furthermore, X-ray irradiation induces generation of trapping centers in NaLuF4:Ho3+ NCs, endowing the generation of mechanoluminescence (ML) behavior upon mechanical stimulation after X-ray irradiation ceases. The ML intensity shows a linear correlation with the X-ray dose, facilitating the detection of delayed radiation. This breakthrough facilitates X-ray dose inspection in flaw detection, nuclear medicine, customs, and civil protection, thereby enhancing opportunities for radiation monitoring and control.

Core-Shell Tandem Catalysis Coupled with Interface Engineering For High-Performance Room-Temperature Na-S Batteries.

The sluggish redox kinetics and shuttle effect seriously impede the large application of room-temperature sodium-sulfur (RT Na-S) batteries. Designing effective catalysts into cathode material is a promising approach to overcome the above issues. However, considering the multistep and multiphase transformations of sulfur redox process, it is impractical to achieve the effective catalysis of the entire S8 →Na2 Sx →Na2 S conversion through applying a single catalyst. Herein, this work fabricates a nitrogen-doped core-shell carbon nanosphere integrated with two different catalysts (ZnS-NC@Ni-N4 ), where isolated Ni-N4 sites and ZnS nanocrystals are distributed in the shell and core, respectively. ZnS nanocrystals ensure the rapid reduction of S8 into Na2 Sx (4 < x ≤ 8), while Ni-N4 sites realize the efficient conversion of Na2 Sx into Na2 S, bridged by the diffusion of Na2 Sx from the core to shell. Besides, Ni-N4 sites on the shell can also induce an inorganic-rich cathode-electrolyte interface (CEI) on ZnS-NC@Ni-N4 to further inhibit the shuttle effect. As a result, ZnS-NC@Ni-N4 /S cathode exhibits an excellent rate-performance (650 mAh g-1 at 5 A g-1 ) and ultralong cycling stability for 2000 cycles with a low capacity-decay rate of 0.011% per cycle. This work will guide the rational design of multicatalysts for high-performance RT Na-S batteries.

Synthesis and Photoluminescence Modulation of Cs4Cd1-xMnxBi2Cl12-Based Two-Dimensional Layered Double Perovskites.

Two-dimensional (2D) layered double perovskites have attracted much attention because of their excellent photoelectric properties. However, few reports have been published on the synthesis of 2D layered double perovskites from halide perovskites as precursors. Here, we report that CsCdCl3 and Cs3Bi2Cl9 were synthesized by the coprecipitation method, and a two-dimensional layered double perovskite Cs4CdBi2Cl12 was readily synthesized by mixing the two halide perovskites. We doped different amounts of Mn2+ into CsCdCl3 to form CsCd1-xMnxCl3, which introduced impurity states into the energy level and exhibited an orange-red light emission that is characteristic of Mn2+. A series of 2D layered double perovskites Cs4Cd1-xMnxBi2Cl12 were synthesized from CsCd1-xMnxCl3 and Cs3Bi2Cl9, which showed a bright orange-yellow luminescence under ultraviolet excitation. The presence of high concentrations of Cd2+ in the two-dimensional layered double perovskites weakened the strong Mn-Mn coupling and suppressed the energy transfer to defects, thus minimizing nonradiative decay and promoting efficient energy transfer. Our work provides a new concept for the synthesis of low-dimensional metal halide perovskites with unique optical properties.

Tailor Traps in Bi3+-Doped NaGdGeO4 Phosphors by Introducing Eu3+ Ions to Switch Multimodal Phosphorescence Emission.

Featured with a tunable excitation/emission wavelength and excellent physicochemical stability, inorganic fluorescent materials are widely used in the fields of anti-counterfeiting. Here, we design a multi-stimuli-responsive dynamic fluorescence and phosphorescence anti-counterfeiting material by introducing Eu3+ ions in NaGdGeO4: Bi3+ to tailor the trap structure. The photoluminescence (PL), long persistent luminescence (LPL), and photo-stimulated luminescence (PSL) colors of NaGdGeO4: Bi3+, Eu3+ can be switched by varying the excitation modes (ultraviolet, near infrared, and X-ray light). Especially, the LPL and PSL colors of NaGdGeO4: Bi3+, Eu3+ vary with increasing decay and stimulation times. In addition, X-ray excitation ensures the specificity of the luminescence of NaGdGeO4: Bi3+, Eu3+ compared with ultraviolet excitation. This rapidly-changing-color fluorescent material offers the possibility of sophisticated anti-counterfeiting applications in the future.

A Temporal and Space Anti-counterfeiting Based on the Four-Modal Luminescent Ba2Zr2Si3O12 Phosphors.

Fluorescent anti-counterfeiting materials have been widely studied due to their high resolution and convenient identification by direct visualization of the color output. To date, the anti-counterfeiting technology of single ultraviolet excitation mode still has security problems because the single mode could be imitated easily. Here, we have successfully developed four modes of anti-counterfeiting from Eu2+ and Er3+ co-doped Ba2Zr2Si3O12 phosphors with photo, long persistent, photo-stimulated, and up-conversion luminescence behavior. The as-fabricated phosphors can emit an intense blue-green luminescence originating from the characteristic transition of Eu2+ ions and exhibit a blue-green long persistent luminescence phenomenon. Moreover, the enhancement of photo-stimulated luminescence that contributed to the effectively increased trap concentration is observed, along with the produced up-conversion phenomenon thanks to the introduction of Er3+ ions. Notably, the fluorescence rapidly changes from blue-green to stable green luminescence with the delay of excitation time under the excitation of a 980 nm laser diode. Herein, this work realizes the fast down- to up-conversion luminescence output over time, which provides the basis for its possible application in advanced multi-mode anti-counterfeiting.

Enhancement of solar-driven photocatalytic activity of oxygen vacancy-rich Bi/BiOBr/Sr2LaF7:Yb3+,Er3+ composites through synergetic strategy of upconversion function and plasmonic effect.

For better use of solar energy, the development of efficient broadband photocatalyst has attracted extraordinary attention. In this study, a ternary composite consisting of Sr2LaF7:Yb3+,Er3+ upconversion (UC) nanocrystals and Bi nanoparticles loaded BiOBr nanosheets with oxygen vacancies (OVs, SLFBB) was designed and synthesized by multistep solvent-thermal method. Mechanisms of in-situ formation of Bi nanoparticles and OVs in BiOBr/Sr2LaF7:Yb3+,Er3+ composites (SFLB) are clarified. The Bi metal and OVs enhanced the light-harvesting capacity in the region of visible-near-infrared (Vis-NIR), and promoted the separation of electron-hole (e-/h+) pairs. Furthermore, the surface plasmon resonance (SPR) effect of Bi metal can improve the energy transfer from Sr2LaF7:Yb3+,Er3+ to BiOBr via nonradiative energy transfer process, resulting in enhancing the light utilization from upconverting NIR into Vis light. Due to the synergistic effects of UC function, SPR and OVs, the SFLBB exhibited obviously enhanced photocatalytic ability for the degradation of BPA with a rate of 8.9 × 10-3 min-1, which is about 2.78 times higher than 3.2 × 10-3 min-1 of BiOBr (BOB) under UV-Vis-NIR light irradiation. This work provides a novel strategy for the project of high-efficiency Bismuth-based broadband photocatalysts, which is helpful to further understand the mechanism of enhanced photocatalysis by UC function and plasmonic effect.

Tailored Luminescence Output of Bi3+-Doped BaGa2O4 Phosphors with the Assistance of the Introduction of Sr2+ Ions as Secondary Cations.

In this work, a tunable luminescence color from yellow to orange of photoluminescence (PL), long persistent luminescence (LPL), and photostimulated luminescence (PSL) is successfully achieved in BaGa2O4:Bi3+ phosphors with the introduction of Sr2+ ions as secondary cations. It is confirmed that broad-band emissions located at 500 and 600 nm originate from the occupation of Bi3+ ions at different lattice sites in the BaGa2O4 host matrix. The replacement of Sr2+ for Ba2+ ions makes the emission red-shift from 600 to 650 nm; moreover, two additional emissions appeare at 743 and 810 nm due to the occupational preference of Bi3+ ions at Ga3+ sites. Furthermore, the doped Sr2+ ions promote the reconstruction of the trapping centers, which conduces to the fundamental improvement of the optical storage capacity behavior of Bi3+-doped phosphors. Our results clarify the dependence of the luminescence performance on the crystal sites of Bi3+ ions with fascinating broad-band emissions in the BaGa2O4:0.01Bi3+ host matrix and will benefit the design and exploration of Bi3+-doped solid solutions for optical storage applications.

Variation from Zero to Negative Thermal Quenching of Phosphor with Assistance of Defect States.

Proper defect states are demonstrated to be beneficial to overcome thermal quenching of the corresponding phosphors. In this work, a cyan-emitting KGaGeO4/Bi3+ phosphor with abundant defect states is reported, the emission intensity of which exhibits an abnormal thermal quenching performance under excitation with different photon energies. A 100% emission intensity is achieved at 393 K under 325 nm excitation compared with that at room temperature, while significantly enhanced intensities of 207% at 393 K and even 351% at 513 K under 365 nm excitation are recorded. The excellent thermal stability performance is confirmed to be not only related to the direct energy transfer from the defect states but also depended on the efficiency of capturing carriers for the trap centers, which is clarified in this work. In addition, the mechanism of the double tunneling process of carriers from trap centers to luminescence centers and luminescence centers to trap centers is studied. These results are believed to provide new insights into the thermal stability of the corresponding fluorescent materials and could inspire studies to further explore novel fluorescent materials with high thermal stability based on defect state engineering.

Broadband, Enhanced, and Antithermally Quenched Near-Infrared Phosphors via a Cosubstitution Approach.

Wearable biosensing and food safety inspection devices with high thermal stability, high brightness, and broad near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) could accelerate the next-generation NIR light applications. In this work, NIR La3-xGdxGa5GeO14:Cr3+ (x = 0 to 1.5) phosphors were successfully fabricated by a high-temperature solid-state method. Here, by doping Gd3+ ions into the La3+ sites in the La3Ga5GeO14 matrix, a 7.9-fold increase in the photoluminescence (PL) intensity of the Cr3+ ions, as well as a remarkably broadened full width at half-maximum (FWHM) of the corresponding PL spectra, is achieved. The enhancements in the PL, PLE intensity, and FWHM are attributed to the suppression of the nonradiative transition process of Cr3+ when Gd3+ ions are doped into the host, which can be demonstrated by the decay curves. Moreover, the La1.5Gd1.5Ga5GeO14:Cr3+ phosphor displays an abnormally negative thermal phenomenon that the integral PL intensity reaches 131% of the initial intensity when the ambient temperature increases to 160 °C. Finally, the broadband NIR pc-LED was fabricated based on the as-explored La1.5Gd1.5Ga5GeO14:Cr3+ phosphors combined with a 460 nm chip, and the potential applications for the broadband NIR pc-LEDs were discussed in detail.

Deep UV random lasing from NaGdF4:Yb3+,Tm3+ upconversion nanocrystals in amorphous borosilicate glass.

The realization of lanthanide-doped upconversion nanocrystals embedded in a robust and transparent solid medium is highly desired to achieve deep UV (<300nm) lasing. Here, we fabricate NaGdF4:Yb3+,Tm3+ upconversion nanocrystals inside amorphous borosilicate glass to support ∼290nm random lasing emission under 980 nm excitation. We found that with careful control of the growth process, which is the key to achieve high-crystallinity nanocrystals, the nanocrystals can suppress defect-related quenching and enhance 1I6→3H6(6IJ→8S7/2) transition of Tm3+ (Gd3+) ions under five-photon absorption excitation so that high optical gain (>45cm-1) at ∼290nm can be obtained.

Ultraviolet C lasing at 263 nm from Ba2LaF7:Yb3+,Tm3+ upconversion nanocrystal microcavities.

It is a daunting challenge to realize ultraviolet C (UVC) lasing (i.e., has a wavelength range from 200 to 275 nm) from upconversion nanocrystals due to their low upconversion efficiency. Here, we fabricate Ba2LaF7:Yb3+(90mol%), Tm3+(5mol%) upconversion nanocrystals from amorphous borosilicate glass to support emission at ∼263nm under 980 nm ns laser excitation. The excitation threshold can be further reduced from ∼130 to ∼26.5mJ/cm2 by using a cylindrical microcavity. We also found that the growth of defect-free Ba2LaF7 nanocrystals with a high concentration of codoping Yb3+ and Tm3+ ions inside high optical damage threshold borosilicate glass is the key to achieving room-temperature UVC upconversion lasing under high-intensity excitation.

Achieving high thermal stability of different rare-earth ions in a single matrix host via the manipulation of the local structure by a solid solution.

Thermal quenching seriously restricts the practical application of phosphors, particularly under high temperature and long-term working conditions. Here, we demonstrate that the as-obtained series of solid solutions of Ca2-xYxAl2Si1-xAlxO7:Tb3+ (x = 0-1, Ca2Al2SiO7 → CaYAl3O7) phosphors exhibit an adjustable optical performance, where CaYAl3O7:Tb3+ exhibits a greatly improved thermal stability with a shortened bond distance of the related polyhedron compared with Ca2Al2SiO7:Tb3+. The shrunken bond distance strengthens the pressure of the local structure and suppresses the non-radiative transition effectively, contributing to the prevention of the thermal degradation. The formed phosphor with excellent structural stability could be effectively incorporated with various lanthanide ions (Eu3+, Tb3+, Sm3+, Dy3+, and Pr3+) to address a pleochroism output.

Extrinsic photoluminescence properties of individual micro-particle of Cs4PbBr6 perovskite with "defect" structure.

Optical performance of the lead halide perovskites with zero-dimension (0D) structure has been in a hot debate for optoelectronic applications. Here, Cs4PbBr6 hexagonal micro-particles with a remarkable green emission are first fabricated via a low-temperature solution-process employed ethanol as solvent. Our results underline that the existence of bromine vacancies and the introduction of hydroxyl induce a narrowed band gap with the formation of a defect level, which contributes to the extrinsic photoluminescence (PL) properties synergistically. Thanks to the high exciton binding energy and the unique morphology with a regular geometric structure of the as-obtained micro-particles, two-photon pumped amplified spontaneous emission (ASE) and single mode lasing from an individual Cs4PbBr6 particle are realized. Our results not only provide an insight into the origin of optical emission from Cs4PbBr6, but also demonstrate that the versatile Cs4PbBr6 offers a new opportunity for novel nonlinear photonics applications as an up-conversion laser.

Study of Crystallization and Coalescence of Nanocrystals in Amorphous Glass at High Temperature.

Amorphous fluoride glass is used as the reaction chamber (i.e., solid cell) to grow Ba2LaF7 (BLF) nanocrystals at elevation temperatures (i.e., 300-500 °C) so that in situ real-time crystallization and coalescence of BLF nanocrystals can be observed. Due to the inherent advantages of the liquid-like solid medium, high temporal and spatial resolution transmission electron microscopy images can be obtained. Hence, we reveal that the twinned and quadruplet BLF nanocrystals are formed at low temperature (≤430 °C) and the unification of two nanocrystals via the two pathways (i.e., migration with and without rotation) to a single defect-free BLF nanocrystal is favored at high temperature (≥470 °C).

Reversible Modulated Upconversion Luminescence of MoO3:Yb3+,Er3+ Thermochromic Phosphor for Switching Devices.

Reversible modulation of upconversion luminescence induced by the external field stimuli exhibits potential applications in various fields, such as photoswitches, optical sensing, and optical memory devices. Herein, a new MoO3:Yb3+,Er3+ thermochromic phosphor was synthesized via a high-temperature solid-state method, and the reversible color modification of the MoO3:Yb3+,Er3+ phosphor was obtained by alternating the sintering conditions either in a reducing atmosphere or in air. The color of the MoO3:Yb3+,Er3+ phosphor changed from light-yellow to blue under sintering in the reducing atmosphere and returned back after sintering again in air. The influence of reversible thermochromism on the upconversion luminescence of MoO3:Yb3+,Er3+ phosphor was investigated. The MoO3:Yb3+,Er3+ phosphor prepared in air exhibited visible upconversion luminescence, while the MoO3:Yb3+,Er3+ phosphor has no upconversion luminescence after sintering in the reducing atmosphere. This up-conversion luminescence modulation shows excellent reproducibility after several cycles. The thermochromic MoO3:Yb3+,Er3+ phosphor with reversible modulated upconversion luminescence shows great potential for practical applications in optical switches and optoelectronic multifunctional devices.

Phase transformation induced reversible modulation of upconversion luminescence of WO3:Yb3+, Er3+ phosphor for switching devices.

The upconverting luminescence properties of phosphors are dependent on the hosts. In this work, the WO3:Yb3+, Er3+ phosphor was prepared, and the reversible phase transformation from the WO3 to the WO2 was obtained by alternating the sintering in a reducing atmosphere or in air. The influence of reversible phase transformation on the upconversion luminescence was investigated first. The WO3:Yb3+, Er3+ phosphor exhibits the visible upconversion luminescence, while no upconversion luminescence was observed in the WO2:Yb3+, Er3+ phosphor. The reversible modulation of upconversion luminescence of the WO3:Yb3+, Er3+ phosphor retains the excellent reproducibility, exhibiting the potential applications in data storage and optical switches.

Comprehensive investigations of near infrared downshift and upconversion luminescence mechanisms in Yb3+ single-doped and Er3+,Yb3+ co-doped SiO2 inverse opals.

Comprehensive investigations of near infrared (NIR) downshift and visible upconversion luminescence (UCL) mechanisms were carried out for Yb3+ single-doped and Er3+,Yb3+ co-doped SiO2 inverse opals under excitation at 256, 378, 520 and 980 nm. NIR emission at 976 nm from the Yb3+-O2- charge transfer state and UCL emission at 500 nm due to the cooperative emission of two Yb3+ ions were observed in SiO2:Yb3+ inverse opal upon excitation at 256 and 980 nm, respectively. The cooperative UCL of two Yb3+ ions was suppressed due to the photon trap created by the photonic band gap. For the SiO2:Er3+,Yb3+ inverse opals, NIR emission of Yb3+ at 976 nm and of Er3+ at 1534 nm were observed upon excitation at 256, 378 and 520 nm, respectively. Upon excitation at 378 and 520 nm, the 976 nm NIR emission of Yb3+ does not arise from (2H11/2/4S3/2) + 2Yb3+(2F7/2) → Er3+(4I15/2) + 2Yb3+(2F5/2) traditional quantum cutting. The NIR emission of Yb3+ at 976 nm may be due to the Er3+(2H11/2) + Yb3+(2F7/2) → Yb3+(2F5/2) + Er3+(4I11/2) cross-relaxation energy transfer process upon excitation at 520 nm. The NIR emission of Yb3+ at 976 nm may arise from the cross-relaxation energy transfer of Er3+(4G11/2) + Yb3+(2F7/2) → Yb3+(2F5/2) + Er3+(4F9/2) and Er3+(4F9/2) + Yb3+(2F7/2) → Yb3+(2F5/2) + Er3+(4I13/2) upon excitation at 378 nm.

Effect of Defect Distribution on the Optical Storage Properties of Strontium Gallates with a Low-Dimensional Chain Structure.

The low-dimensional structure of the SrGa2O4 host exhibits a self-activated long persistent luminescence related to the creation of the oxygen vacancies. Because of the unique structure of the SrGa2O4 with a chain of cations along the a crystal direction, the emission and trapping centers could be introduced easily when the metal ions of Bi(3+) are doped. Both the photoluminescence and long persistent luminescence are related to two efficient emission centers of Bi(3+) in the two different crystallographic Sr sites, while the photostimulated luminescence spectra exhibit only one emission center of Bi1 ions under excitation at 980 or 808 nm. The results indicate that the distribution of defects in the low-chain structure of the SrGa2O4 host plays a vital role in the capture and transfer processes of carriers, which has a profound influence on the luminescence performance of SrGa2O4:Bi(3+) as one of the electron-trapping materials.