Hydrothermal synthesis of ZnGa2O4 nanophosphors with high internal quantum efficiency for near-infrared pc-LEDs.

NIR luminescent materials have garnered widespread attention because of their exceptional properties, with high tissue penetration, low absorption and high signal-to-noise ratio in the field of optical imaging. However, producing nanophosphors with high quantum yields of emitting infrared light with wavelengths above 1000 nm remains a significant challenge. Here, we prepared a nanoscale ZnGa2O4:xCr3+,yNi2+ phosphor with good luminescence performance in near-infrared emission, which was synthesized via a hydrothermal method and subsequent calcination process. By co-doping with Cr3+ and Ni2+, the ZnGa2O4 phosphor shows a strong broadband emission of 1100-1600 nm in the second near-infrared (NIR-II) region, owing to the energy transfer from Cr3+ to Ni2+ with an efficiency up to 90%. Meanwhile, a near-infrared phosphor-conversion LED (NIR pc-LED) device is fabricated based on the ZnGa2O4:0.8%Cr3+,0.4%Ni2+ nanophosphor, which has under 100 mA input current, an output power of 23.99 mW, and a photoelectric conversion efficiency of 7.53%, and can be effectively applied in imaging and non-destructive testing. Additionally, the intensity ratio of INi/ICr of ZnGa2O4:0.8% Cr3+,0.4%Ni2+ with its high sensitivity value of 4.21% K-1 at 453 K under 410 nm excitation, indicates its potential for thermometry application.

Efficient and zero thermal quenching Sm3+-activated Li2LaTiTaO7 phosphor for white LEDs.

In this work, we prepared a new orange-red phosphor Li2La1-xTiTaO7:xSm3+ (abbreviated as LLTT:Sm3+) for white light-emitting diodes (w-LEDs). Its crystal structure, microstructure, photoluminescence characteristics, luminescence lifetime and thermal quenching properties were studied in depth. The LLTT:Sm3+ phosphor shows four intense emission peaks at 563, 597, 643, and 706 nm when excited at 407 nm. Thermal quenching is caused by the dipole-quadrupole (d-q) interaction of Sm3+ ions, and the optimum doping concentration of Sm3+ is x = 0.05. Meanwhile, the LLTT:0.05Sm3+ phosphor has a high overall quantum yield (QY = 59.65%) and almost no thermal quenching. The emission intensity at 423 K is 101.5% of the initial value at 298 K, while the CIE chromaticity coordinates barely change as the temperature rises. The fabricated white LED device exhibits excellent CRI and CCT values of 90.4 and 5043 K, respectively. These findings demonstrate that the LLTT:Sm3+ phosphor has promise in w-LED applications.

Lanthanide-doped Na2MgScF7 exhibiting downshifting and upconversion emissions for multicolor anti-counterfeiting.

Na2MgScF7 (NMSF) was experimentally obtained for the first time by combining hydrothermal and high-temperature solid-state reactions. X-ray powder diffraction (XRD) combined with Rietveld refinement confirms that NMSF is crystallized in the space group Imma with the cell parameters a = 10.40860(18), b = 7.32804(12) and c = 7.52879(11) Å, α = ß = γ = 90° and V = 574.256(24) Å3. Through doping with Tb3+ or Eu3+ ions, downshifting yellow-green or red emission could be achieved in NMSF-based phosphors, respectively. Upconversion emission could also be designed by doping with Yb3+-Er3+, Yb3+-Tm3+, Yb3+-Ho3+ or Er3+. Moreover, the NMSF:Er3+ phosphor exhibited green upconversion emission upon excitation at 980 nm, and it exhibited red emission upon excitation at 1532 nm. Finally, recognizable patterns were obtained under excitation at 254, 365 and 980 nm, indicating that the as-prepared phosphors can be applied to multicolor anti-counterfeiting. Moreover, our synthesis strategy opens up new avenues for the synthesis of novel fluorides.

Multiple site occupancy induced yellow-orange emission in an Eu2+-doped KSr6Sc(SiO4)4 phosphor towards optical temperature sensors.

Phosphors have attracted significant interest as potential optical temperature sensors in recent years. In our work, a new blue-light stimulated KSr6Sc(SiO4)4:Eu2+ phosphor with decorative kröhnkite-like octahedral tetrahedral chains was successfully synthesized. Multiple site occupancy occurred in KSr6Sc(SiO4)4:Eu2+ and induced a yellow-orange emission band with a peak at 571 nm and an FWHM of 91 nm. Gaussian fitting and time-resolved photoluminescence mapping were combined to analyze the occupation of Eu2+ in five Sr2+ sites. In the meantime, the site occupation preference, energy transfer process, and thermal quenching mechanism of Eu2+ emission centers have been comprehensively examined. Under 450 nm excitation, the optimal sample possesses an acceptable quantum efficiency (EQE = 17.3%) and a high sensitivity between luminescence properties and temperature variation ranging from 200 to 475 K. The optimal sample's relative sensor sensitivity achieves a maximum value of 3.53% K-1 at 475 K. The phosphor KSr6Sc(SiO4)4:0.07Eu2+ presents the potentiality as an optical thermometer.

Achieving High Quantum Efficiency Broadband NIR Mg4 Ta2 O9 :Cr3+ Phosphor Through Lithium-Ion Compensation.

Ultra-efficient broadband near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are urgently needed to improve the detection sensitivity and spatial resolution of current smart NIR spectroscopy-based techniques. Nonetheless, the performance of NIR pc-LED has severely limited owing to the external quantum efficiency (EQE) bottleneck of NIR light-emitting materials. Herein, a blue LED excitable Cr3+ -doped tetramagnesium ditantalate (Mg4 Ta2 O9 , MT) phosphor is advantageously modified through lithium ion as a key efficient broadband NIR emitter to achieve high optical output power of the NIR light source. The emission spectrum encompasses the 700-1300 nm electromagnetic spectrum of first biological window (λmax  = 842 nm) with a full-width at half-maximum (FWHM) of ≈2280 cm-1 (≈167 nm), and achieves a record EQE of 61.25% detected at 450 nm excitation through Li-ion compensation. A prototype NIR pc-LED is fabricated with MT:Cr3+ , Li+ to evaluate its potential practical application, which reveals an NIR output power of 53.22 mW at a driving current of 100 mA, and a photoelectric conversion efficiency of 25.09% at 10 mA. This work provides an ultra-efficient broadband NIR luminescent material, which shows great promise in practical applications and presents a novel option for the next-generation high-power compact NIR light sources.

Resolving the stacking fault structure of silver nanoplates.

The stacking fault structure (SFT) is the key to understanding the symmetry breaking of fcc nanocrystals and the origin of two-dimensional (2D) anisotropic growth of nanoplates. After resolving the SFT in Ag nanoplates under aberration-corrected transmission electron microscope (TEM) observations, it is found that there are three basic stacking faults, namely, twinned stacking fault (SF-t), a layer missed stacking fault (SF-m) and a layer inserted stacking fault (SF-i). The SFT is composed of one or a combination of two or all of the three kinds of stacking faults with a total number varying from 4 to 9. It has been demonstrated that the SFT could generate concave faces, step faces and (100) faces in the lateral directions, which provides sites for adding-atoms with a higher coordination number than on the top and bottom flat (111) faces, and results in the anisotropic growth along the 2D direction. Additionally, Ag nanoplates fall into either center symmetry or mirror symmetry when the corresponding number is even or odd. The center symmetry and mirror symmetry with different side face arrangements in turn manipulate the shape evolution to cubes and bipyramids, respectively. Our study provides a comprehensive understanding of the formation and growth of 2D metal nanomaterials.

Synthesis and ORR electrocatalytic activity of mixed Mn-Co oxides derived from divalent metal-based MIL-53 analogues.

The design of efficient mixed Mn-Co oxides as oxygen reduction reaction (ORR) electrocatalysts in alkaline media has been boosted nowadays. Recently, multivariant MOFs have been demonstrated as versatile precursors to construct these mixed metal oxides. Herein, we synthesized four mixed Mn-Co oxide samples via simply annealing their MIL-53 precursors with different Co/Mn molar ratios. These four samples were dominated by three kinds of Mn-Co spinel phases. The mixed Mn-Co oxides showed enhanced ORR performances compared with the single metal counterparts in alkaline media. In particular, the sample containing a pure MnCo2O4 phase exhibited the highest activity with a half-wave potential of 0.772 V (vs. RHE), only 40 mV negative compared with that of commercial Pt/C. The H2O2 yield was calculated to be below 12.1%, corresponding to the high diffusion-limited current density along with the high electron transfer number. The surface defects, active Mn4+/Mn3+ and electrochemically active surface area together affected the ORR performances of these mixed Mn-Co oxides. The present work highlights the facile controllability of divalent MIL-53 analogues for highly efficient mixed Mn-Co oxides in ORR electrocatalysis.

Precise Control of the Lateral and Vertical Growth of Two-Dimensional Ag Nanoplates.

Tuning localized surface plasmon resonance (LSPR) is crucial for practical applications of two-dimensional Ag nanoplates (AgNPs) and relies on the precise control of their lateral length or/and thickness. In the present seed-mediated synthetic method, by taking advantage of underpotential deposition (UPD) of Cu on the (111) surfaces of AgNPs, a solely lateral growth of AgNPs was achieved when Cu(NO3 )2 was employed, while a vertical growth of AgNPs could be attained by introducing CuCl2 into our growth solutions. The lateral length and the vertical thickness of the AgNPs could be tuned in the ranges of 115 to nearly 300 nm and 13.4 to around 200 nm, respectively. Along with control of the dimensional size of AgNPs, LSPR could also be tuned in the visible to near infrared range. Plausible growth mechanisms for the precise control of the lateral and vertical growth of AgNPs were proposed.

Cu2O-directed in situ growth of Au nanoparticles inside HKUST-1 nanocages.

Controllable integration of metal nanoparticles (MNPs) and metal-organic frameworks (MOFs) is attracting considerable attention as the obtained composite materials always show synergistic effects in applications of catalysis, delivery, as well as sensing. Herein, a Cu2O-directed in situ growth strategy was developed to integrate Au nanoparticles and HKUST-1. In this strategy, Cu2O@HKUST-1 core-shell heterostructures, HKUST-1 nanocages, Cu2O@Au@HKUST-1 sandwich core-shell heterostructures and Au@HKUST-1 balls-in-cage heterostructures were successfully synthesized. Cu2O@HKUST-1 core-shell heterostructures were synthesized by soaking Cu2O nanocrystals in benzene-1,3,5-tricarboxylic acid solution. The well-defined Cu2O@HKUST-1 core-shell heterostructures were demonstrated to be dominated by the ratio of Cu2+ cations to btc3- ligands in solution during the period of HKUST-1 formation. Cu2O@Au@HKUST-1 sandwich core-shell or Au@HKUST-1 balls-in-cage heterostructures were obtained by impregnating HAuCl4 into Cu2O@HKUST-1 core-shell heterostructures. Due to the porosity of HKUST-1 and reducibility of Cu2O, HAuCl4 could pass through the HKUST-1 shell and be reduced by the Cu2O core in situ forming Au nanoparticles. Finally, CO oxidation reaction at high temperatures was carried out to assess the catalytic functionality of the obtained composite heterostructures. This strategy can circumvent some drawbacks of the existing approaches for integrating MNPs and MOFs, such as nonselective deposition of MNPs at the outer surface of the MOF matrices, extreme treatment conditions and additional surface modifications.

LSPR-dependent SERS performance of silver nanoplates with highly stable and broad tunable LSPRs prepared through an improved seed-mediated strategy.

The application of the silver plates as a proper substrate for surface enhanced Raman spectroscopy (SERS) was performed to give deep insight on LSPR-dependent SERS performance. Firstly, an improved seed-mediated method is developed to synthesize silver nanoplates (NP) with broad-tuning localized surface plasmon resonance (LSPR) and high stability. The LSPR peaks could be tuned in the range from 485 to ∼1200 nm by controlling the experimental parameters. With the treatment of sodium dodecyl sulfate (SDS), silver NPs exhibit high stability for SERS tests. The LSPR-dependent SERS study was performed by taking four typical silver NPs with LSPR peaks at 485 nm, 614 nm, 906 nm and 1130 nm as substrates. Also, two probe molecules, 4-amino-thiophenol (4-ATP) and rhodamine-6G (R-6G), were used, and both the 458 nm and 633 nm lasers were selected as excitation for the LSPR-dependent SERS study. Our results indicated that the SERS performance is largely dependent on the LSPR of the silver NP substrate at a given excitation wavelength. Specifically, the Raman signals were greatly enhanced when the laser excitation line matched (close to the LSPR band) the peak position of LSPR band. When at the excitation of 633 nm, two orders of magnitude stronger SERS signals would be observed for the Ag-614 substrate than that of the Ag-485 and Ag-1130 substrates with their LSPR peak positions far away from 633 nm. The same result can also be observed when the laser excitation at 458 nm was selected for the Ag-485 substrate. Our study gives a deep insight into LSPR-dependent SERS performance. It also gives a method for giving large SERS enhancement just by selecting a proper excitation wavelength matched to the LSPR of the substrate.

Low-Pt loaded on a vanadium nitride/graphitic carbon composite as an efficient electrocatalyst for the oxygen reduction reaction.

The high cost of platinum electrocatalysts for the oxygen reduction reaction (ORR) has hindered the commercialization of fuel cells. An effective support can reduce the usage of Pt and improve the reactivity of Pt through synergistic effects. Herein, the vanadium nitride/graphitic carbon (VN/GC) nanocomposites, which act as an enhanced carrier of Pt nanoparticles (NPs) towards ORR, have been synthesized for the first time. In the synthesis, the VN/GC composite could be obtained by introducing VO3 (-) and [Fe(CN)6 ](4-) ions into the polyacrylic weak-acid anion-exchanged resin (PWAR) through an in-situ anion-exchanged route, followed by carbonization and a subsequent nitridation process. After loading only 10 % Pt NPs, the resulting Pt-VN/GC catalyst demonstrates a more positive onset potential (1.01 V), higher mass activity (137.2 mA mg(-1) ), and better cyclic stability (99 % electrochemical active surface area (ECSA) retention after 2000 cycles) towards ORR than the commercial 20 % Pt/C. Importantly, the Pt-VN/GC catalyst mainly exhibits a 4 e(-) -transfer mechanism and a low yield of peroxide species, suggesting its potential application as a low-cost and highly efficient ORR catalyst in fuel cells.

In Situ intercalating expandable graphite for mesoporous carbon/graphite nanosheet composites as high-performance supercapacitor electrodes.

Mesoporous-carbon-coated graphite nanosheet (GNS@MC) composites have been synthesized by the intercalation of resol prepolymer into the interlayers of expandable graphite (EG) under vacuum-assisted conditions, followed by the exfoliation of EG through in situ polymerization, the growth of resol under hydrothermal conditions, and carbonization under Ar. The GNS@MC composites exhibit enhanced capacitive performance compared to mesoporous carbon (MC), microwaved EG after thermal treatment (T-EG), and the physical mixture of MC and T-EG (MC+T-EG). In particular, the GNS@MC-35-800 composite carbonized at 800 °C, which has a graphite-nanosheet content of 35 % and a Brunauer-Emmett-Teller surface area (S(BET) ) of 432.3 m(2) g(-1) , exhibits the highest capacitance of 203 F g(-1) at 1 A g(-1) in 6 M KOH electrolyte. Furthermore, the GNS@MC-35-800 composite exhibits a good cyclic stability with 95 % capacitance retention and a high columbic efficiency of 99 % after 5000 cycles. The energy density of the symmetric supercapacitor GNS@MC-35-800/GNS@MC-35-800 achieved was as high as 11.5 Wh kg(-1) at a high power density of 10 kW kg(-1) . This good performance is attributable to the GNSs in the GNS@MC composite facilitating electron transport owing to its excellent conductivity; moreover, the MC in GNS@MC favors the rapid diffusion of ions by providing low-resistance pathways. The GNS@MC composite may find application in high-performance energy storage and conversion devices.

Fabrication of small-sized silver NPs/graphene sheets for high-quality surface-enhanced Raman scattering.

In this paper, small-sized and highly dispersed Ag nanoparticles (NPs) supported on graphene nanosheets are fabricated via a strategy for etching a copper template with Ag(+). Firstly, big-sized Cu NPs are supported on graphene, and then the small-sized and highly dispersed Ag NPs are supported on graphene by replacement reaction, mainly making use of graphene passing electrons between Cu and Ag(+). The graphene used in the experiment is prepared by in situ self-generating template and has good dispersion, excellent crystallinity and little defects. Thus, in the process of Ag/graphene synthesis, there is no any intervention of surfactant, which ensures that SERS activity sites have not been passivated. And, the little defects of graphene benefit the excellent conductivity of graphene and ensured the replacement reaction between Cu and Ag(+). The obtained material exhibits significant high-quality and distinctive SERS activity. Especially, a serial new peak of p-aminothiophenol (PATP) is observed, this is suggested two reasons: one is "surface geometry" of the PATP on small-sized Ag NPs and another is the charge-transfer between Ag and graphene.