Search

Red phosphors play an important role in improving the light quality and color rendering index of white light-emitting diodes (WLEDs) for lighting. In this paper, we report the transition ion Mn4+-activated deep red phosphor GdGeSbO6:x%Mn4+ and analyze its crystal structure, composition and luminescence behavior in detail. Its optimal doping concentration of Mn4+ is 0.3%. Under ultraviolet (UV) excitation, GdGeSbO6:0.3%Mn4+ produces a narrow emission peak centred at 682 nm in the range of 650–800 nm with a full width at half maximum (FWHM) of 25 nm, which is attributed to the spin-prohibited 2Eg → 4A2g transition of Mn4+ ions. Notably, the optimal phosphor GdGeSbO6:0.3%Mn4+ has a high internal quantum efficiency (IQE ≈ 65%) and excellent thermal stability performance (I423 K/I303 K ≈ 62%). The synthesis of high-performance warm WLEDs and full-spectrum WLEDs was achieved by combining and coating GdGeSbO6:0.3%Mn4+ phosphors with commercial phosphors on the surface of a 365 nm UV chip. [ABSTRACT FROM AUTHOR]

Mn ions in different valence states can emit light of different colors in an octahedral coordination environment, which is conducive to the development of a single matrix with multi-color luminescence and applications in the field of anti-counterfeiting. The dual mode multi-color luminescent material CaSb 2 O 6 : Mn has been successfully synthesized using a single Mn source in the atmosphere. The CaSb 2 O 6 matrix itself can also absorb 285 nm UV light, emit blue light, and show a long afterglow phenomenon. Both Mn4+ and Mn2+ ions will appear in the [SbO 6 ] octahedra, whether the Mn source adopts MnCO 3 or MnO 2. The Mn4+ ion exhibits red emission upon UV excitation at 347 nm. The Mn2+ ion can emit a bright green light at 285 nm excitation while exhibiting a long afterglow phenomenon. In this study, the Mn2+ doped octahedron showed unique green emission and broadens the range of its photoluminescence (PL) wavelength. The performance of the material's long afterglow properties on the digital codes demonstrates its potential for dynamic anti-counterfeiting. [ABSTRACT FROM AUTHOR]

The optical properties of Mn4+-activated phosphors are heavily affected by the host and the related data are difficult to obtain, which makes quantitative design of novel phosphors with required wavelength particularly challenging. In the era of big data, computation is emerging as a vital complement to materials development. Compared with traditional calculation routes, machine learning (ML) models provide better solutions for the problems wherein understanding the underlying physics is complicated with sparse data. In this study, we developed six ML models based on a sparse and small data set to rapidly predict the peak emission wavelength of novel phosphors and use Recursive Feature Elimination (RFE) to select the best features. Among them, the K-nearest neighbors regression (KNN.r) algorithm using non-parametric regression technology can predict the value of the target variable based on the similarity between the target value and its spatial neighbors, which can tackle sparse data sets with no obvious linear relationship well and has the best prediction accuracy. These models were then used to predict 278 potential Mn4+-activated phosphor hosts extracted from the inorganic crystal structure database (ICSD), and 19 samples were selected to validate these methods. In order to overcome the lack of physical and chemical insight of KNN, a visual data analysis was carried out based on hierarchical clustering analysis (HCA), and the rule between the peak emission wavelength and the structure of host was proposed. Guided by the results of KNN and HCA, six samples were selected for the synthesis and characterization to verify our conclusions. The measured values of all these phosphors exhibit good agreement with the predicted results, suggesting the success of our methodology. Thus, the model established and the rule proposed in this paper provide a new pathway for the rapid discovery of novel phosphors. [ABSTRACT FROM AUTHOR]

At present, tuning the luminescence characteristics of phosphors by external physical stimuli such as temperature and pressure has attracted the interest of researchers. However, the emission-tunable luminescence processes by temperature or pressure in lead-free perovskite with ordered vacancy materials have not been systematically studied. In this study, Bi3+-doped Rb2SnCl6 crystals were successfully synthesized using a simple precipitation method, and these crystals demonstrated a remarkable enhancement of luminescence intensity compared with the unannealed ones at 140–200 °C, and with a red-shift in the emission peak from 450 to 500 nm. It was found that the annealing treatment increased the Bi–Cl bond length leading to emission red-shift and achieved the change in the emission intensity due to the band gap modulation of the material. Furthermore, a candidate material for the color-changing optical security strategies was obtained by combining the Bi3+-doped Rb2SnCl6 phosphor and printing ink. This work is a valuable reference for the rational design of luminescent perovskites with promising new functionalities and stimulates the great potential of luminescent perovskites in developing promising phosphors for advanced anticounterfeiting. [ABSTRACT FROM AUTHOR]

Far-red phosphors with higher thermal stability and exhibit excellent spectral compatibility with the far-red light phytochrome (P FR) absorption spectrum. They are currently a research hotspot and widely applied in plant growth lamps. In this study, we have prepared a Mn4+-activated Sr 2 ScNbO 6 far-red phosphor by using the high temperature solid phase method in air. The strongest excitation center of the Sr 2 ScNbO 6 : Mn4+ phosphor was located at 365 nm. Due to the 2E g →4A 2 g transition, this phosphor generates strong deep-red light at 703 nm, which significantly overlaps with the absorption spectrum of plant phytochrome P FR. The variable temperature photoluminescence (PL) emission spectra from 303 K to 503 K confirmed this phosphor possesses relatively good thermal stability. In addition, the concentration quenching effect and the thermal quenching mechanism are studied in detail. The results demonstrate that Sr 2 ScNbO 6 : 0.4 % Mn4+ phosphor provides a novel choice for the far-red phosphor required for short-day plant cultivation. • A double perovskite phosphor Sr 2 ScNbO 6 : Mn4+ was synthesized. • Sr 2 ScNbO 6 : Mn4+phosphor shows relatively good thermal stability, I 423 K /I 303 K ≈ 44 %. • The Mn4+ far-red emission matches well with the absorption spectral of P FR. • The materials show promising application in the field of short-day plant cultivation. [ABSTRACT FROM AUTHOR]

Te4+-doped Cs2ZrCl6 vacancy-ordered perovskites with excitation wavelength-dependent tunable color have been synthesised by a simple precipitation method at room temperature, with two luminescent centres originating from the Te4+ and the STE (self-trapping exciton) of the Cs2ZrCl6 itself, respectively. They exhibit two different emission characteristics at 254 nm and 365 nm excitation wavelengths. At an excitation wavelength of 254 nm, the emission characteristics allow Te4+-doped Cs2ZrCl6 to exhibit tunable emission from blue to white to yellow under the control of Te4+ doping. And the excitation wavelength of 365 nm shows yellow emission. Te4+ doped Cs2ZrCl6 phosphors were used for optical anti-counterfeiting, and the anti-counterfeiting patterns were well distinguished under 254 nm and 365 nm UV lamps, demonstrating the potential of this excitation wavelength-dependent tunable color material for optical anti-counterfeiting applications. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) are a unique class of multifunctional hybrid crystals that have been successfully utilized in diverse ranges of applications. However, since MOFs are prone to aqueous degradation, the development of stable luminescent MOF platforms in aqueous media is still a huge challenge. Here, a novel dual-ligand Eu3+/DUT-52-COOH composite is prepared based on the luminescent DUT-52 prototype structure via a dual-ligand strategy and a post-synthetic modification (PSM) method. The functionalized Eu3+/DUT-52-COOH material exhibits dual emission and good photothermal stability in aqueous media. Thus, Eu3+/DUT-52-COOH is developed as a ratiometric luminescent sensor to achieve highly selective and sensitive detection of Cu2+ and Cr2O72− in aqueous solutions and has a low detection limit of 3.43 μM and 25.7 nM, respectively. This work is one of the few cases of detecting Cu2+ and Cr2O72− in aqueous media based on a DUT-52, and the detection signals can be observed by the bare eye without using sophisticated analytical instruments. The possible sensing mechanism is discussed in detail. The results obtained in this project may provide broad prospects for developing smart sensing systems to accomplish highly efficient, easily operable and quantitative intelligent recognition of Cu2+ and Cr2O72−. [ABSTRACT FROM AUTHOR]

Here we have developed a facile and rapid colorimetric method for the sensitive and selective detection of Ag+ based on the non-aggregation of gold nanoparticles (Au NPs) capped with hyperbranched polyethylenimine derivatives. In the detection process, an unusual colour change from red to brown was observed due to the formation of Au–Ag core–shell nanoparticles, which was more sensitive than that of the usual colorimetric assays (red to blue) based on the aggregation of Au NPs. After the colour changed, the non-aggregation-based Au–Ag core–shell nanomaterials did not aggregate further and could remain stable for a long time, which was convenient to record, detect and observe. The sensing probe exhibited a drastically long observing time for detecting Ag+ owing to the stability of the Au–Ag core–shell non-aggregates, high sensitivity with a low detection limit of 8.76 nM by the naked eye and 1.09 nM by using a UV-vis spectrophotometer and a good linear relationship within the range from 1.09 to 109 nM. The colour change of the system is very fast, occurring within 1 to 2 minutes. Moreover, the proposed method also showed a remarkably high selectivity toward Ag+ and was successfully used in tap water and drinking water samples. Therefore, this unusual colorimetric assay based on the non-aggregation of Au NPs has a great potential as a simple, rapid, sensitive and selective detection method for the detection of Ag+. [ABSTRACT FROM AUTHOR]

Red LEDs excited by blue light have a wide range of applications in plant growth due to their simple structure. The preparation of efficient red phosphors has attracted much attention from researchers. In this paper, Cs 2 NaGdCl 6 :Ho3+ Sb3+ phosphors were synthesized by the solvothermal method, which produced the characteristic emission of Ho3+ 5 F5→ 5 I8 at 655 nm under 460 nm excitation. The red light at 655 nm is further enhanced after the introduction of Sb3+, and the quantum efficiency can reach 39.85 %. The luminescence mechanism and energy transfer of Sb3+ and Ho3+ were further investigated. The produced phosphor was encapsulated with a 460 nm blue chip into an LED to realize red and blue dual emission, which meets the demand for blue and red light for plant growth. • A double perovskites phosphor Cs 2 NaGdCl 6 :Ho3+ Sb3+ was synthesized. • The emission spectrum excited by the blue light chip matches well with the plant absorption spectrum. • Synthesis of a halide double perovskites with good thermal stability. • The materials show promising application in the field of plant cultivation. [ABSTRACT FROM AUTHOR]

• Amino acid modified wood solves the disadvantage of high cost and difficult separation of chiral catalysis. • Wood natural tertiary channels are fully utilized to enhance mass flow and promote catalytic reactions. • The stable bonding of amino acids not only improves performance, but also prolongs the lifetime of the catalyst. Molecular sieve catalysts have been adopted in chiral catalytic reactions due to their high specific surface area, nano-scaled pores and effective separation, however, the problems like low utilization ratio of channels, difficult modification, long period and complex preparation, and no economic benefits reduce its widely application. In this paper, natural wood was employed as raw material to preserve the cellulose skeleton rich in poly‑hydroxyl and the multistage porous channels of nanometer, micron and millimeter by simple treatment. A low-cost, high-yield and high-selectivity chiral catalyst could be obtained from wood with chiral catalytic sites. The in situ grafting method retains the well-developed multistage pore structure of wood, enhances the mass transfer and possesses universal applicability to different aldol condensation reactions. The asymmetric reaction of cyclohexanone and p-nitrobenzaldehyde is catalyzed by grafting readily available amino acids such as threonine, with a yield of 82% and selectivity of 57%. Molecular sieve-like wood possesses the advantages of low economic cost and good catalytic performance, which provides a potential possibility to replace traditional molecular sieve catalyst. [Display omitted] [ABSTRACT FROM AUTHOR]

Luminescent dye molecules have attracted enormous research interest, whereas, there are inherent drawbacks that limit their utilization across a broad variety of fields. Herein, a novel dual-luminescent carboxylic acid functionalization Eu3+/Hoc@UIO-66(H 3 BTC) (Hoc = 7-hydroxycoumarin) was prepared by introducing luminescent dye molecules (Hoc) into the UiO-66-type dual-ligand metal−organic frameworks (MOFs) utilize the encapsulation approach and postsynthetic modification (PSM). UIO-66(H 3 BTC) was constructed using 1,4-dicarboxybenzene (TPA) as the first ligand, which can restrict the aggregation-induced quenching of Hoc dyes and maintains the Hoc dyes stably included after preparation. 1,3,5-benzenetricar boxylic acid (H 3 BTC) was used as a second ligand to sensitize Eu3+ ions for the antenna effect emission and provide detection sites. Eu3+/Hoc@UIO-66(H 3 BTC) material possesses blue luminescence from Hoc molecules as well as red luminescence from Eu3+ when irradiated by UV lamp, which can be used for ratiometric luminescence detection of Cu2+/Fe3+ through reference to the intensity ratios of two emitting peaks. Eu3+/Hoc@MOFs(H 3 BTC) as a luminescence sensor, displays an ultrahigh sensitivity (Cu2+:4.58 μM, Fe3+:18 μM), strong ant-interference ability, and fast response for detecting analytes. This project demonstrates that the dual-ligand Zr-based MOFs and luminescence dyes offers a novel ratiometric luminescence detection platform for heavy metal ions visible identification. • MOFs includes free –COOH groups that can sensitize Eu3+ ions to realize luminescence and provide site-specific assays. • Eu3+/Hoc@UIO-66(H 3 BTC) overcome (ACQ) effects to encapsulate Hoc dye molecule luminescence. • The advantages of dye encapsulation for detection are proven, with dual emission improving sensitivity. • The ratiometric sensor possess a wide linear concentration range, low LOD and visible detection. [ABSTRACT FROM AUTHOR]

The crystal phase and energy band adjustment of halide perovskites have become the focus of research. Sb3+ doped lead-free indium-based perovskites A 2 InX 5 ·H 2 O:Sb3+ (A=Cs+, Rb+; X = Cl-, Br-) are synthesized at room temperature. Through changing the crystal phase structure, an intelligent anti-counterfeiting material is used to monitor water vapor and high temperature. Moreover, the Rb 2 InBr 5 ·H 2 O:Sb3+ achieves broadband near-infrared (NIR) emission with a high photoluminescence quantum efficiency (PLQY) of 54.3%. The NIR light-emitting diode shows that the device can effectively achieve NIR imaging. Theoretical calculations further clarified that the regular changes in luminescence originate from energy band modulation. This work provides a broader sight for the synthesis, luminescence mechanism and application of indium-based perovskite. • Indium-based perovskite with controllable luminescence properties was synthesized at room temperature. • The reversible change of crystal phase is used for smart anti-counterfeiting. • High-efficiency quantum yield of Rb 2 InBr 5 ·H 2 O:Sb3+ is used in near-infrared light-emitting diodes. • Theoretical calculation combined with experiments prove that broadband emission originate from band gap adjustment. [ABSTRACT FROM AUTHOR]

Three-dimensional CuCo 2 O 4 @MnMoO 4 core/shell nanosheet arrays grown on nickel foam were designed and prepared through two-step hydrothermal processes followed by a low-temperature thermal treatment. The interconnected CuCo 2 O 4 nanosheets are uniformly decorated by ultrathin MnMoO 4 nanoflakes, forming highly porous hierarchical networks. The electrochemical results reveal that the binder-free CuCo 2 O 4 @MnMoO 4 electrode exhibits a superb specific capacitance of 1327.5 F g−1 at 1 A g−1 and remarkable cycling stability (maintaining 92.8% of initial capacitance over 6000 cycles). The superior supercapacitive properties can be ascribed to the high mechanical stability, large surface area, high electron/ion transfer rate, and the strong synergistic contribution from CuCo 2 O 4 and MnMoO 4. Additionally, the assembled CuCo 2 O 4 @MnMoO 4 //graphene hybrid supercapacitor device delivers a maximum specific energy of 58.9 Wh kg−1 at a specific power of 670 W kg−1, manifesting the great potential of the CuCo 2 O 4 @MnMoO 4 core/shell nanosheet arrays as advanced electrode materials for energy storage systems. [ABSTRACT FROM AUTHOR]