Construction of a Defective Chiral Covalent Organic Framework for Fluorescence Recognition of Amino Acids.

The design and synthesis of chiral covalent organic frameworks (COFs) with controlled defect sites are highly desirable but still remain largely unexplored. Herein, we report the synthesis of a defective chiral HD-TAPB-DMTP COF by modifying the chiral monomer helicid (HD) into the framework of an achiral imine-linked TAPB-DMTP COF using a chiral monomer exchange strategy. Upon the introduction of the chiral HD unit, the obtained defective chiral HD-TAPB-DMTP COF not only displays excellent crystallinity, large specific surface area (up to 2338 m2/g) and rich accessible chiral functional sites but also exhibits fluorescence emission, rendering it a good candidate for discrimination of amino acids. Notably, the resultant defective chiral HD-TAPB-DMTP COF can be used as a fluorescent sensor for enantioselective recognition of both tyrosine and phenylalanine enantiomers in water, showing enhanced fluorescent responses for the L conformations over those of the D conformations with enantioselectivity factors being 1.84 and 2.02, respectively. Moreover, molecular docking simulations uncover that stronger binding affinities between chiral HD-TAPB-DMTP COF and L-tyrosine/L-phenylalanine in comparison to those with D-tyrosine/D-phenylalanine play important roles in enantioselective determination. This work provides new insights into the design and construction of highly porous defective chiral COFs for enantioselective fluorescence recognition of amino acids.

Hydrothermal and anion exchange synthesis of Mn(V)-doped Ba5(PO4)3Cl nano-apatite toward NIR-II temperature sensing.

The second near-infrared window (NIR-II) in the range of 1000-1400 nm is ideal for in vivo imaging and sensing through reduced scattering, absorption, and autofluorescence. However, there are only a few nanophosphor systems with emission in the NIR-II region. Here, we report on Mn5+-doped Ba5(PO4)3Cl nanoparticles (BPCl:Mn5+ NPs, d < 50 nm) toward NIR-II temperature sensing. BPCl:Mn5+ NPs are made by a two-step (hydrothermal and anion exchange) method. XRD, SEM, and TEM results showed that the as-prepared BPCl:Mn5+ NPs show high crystallinity, uniform size, and sphere-like morphology. The nanoparticles exhibit a broad excitation band of 500-850 nm and a temperature-sensitive peak emission at 1175 nm in the NIR-II range. NIR-II temperature sensing by 1E emission intensity is demonstrated with good linear fitting (R2 = 0.9895), high sensitivity (2.30% at 373 K), and good repeatability (99.0%). Thus, our study provides a path to develop a new NIR-II thermometer based on tetrahedral Mn(V) coordination.

Preparation and characterization of functionalized chitosan/polyvinyl alcohol composite films incorporated with cinnamon essential oil as an active packaging material.

In this study, amphiphilic chitosan (NPCS-CA) was synthesized by grafting quaternary phosphonium salt and cholic acid onto the chain of chitosan, aiming to develop an active edible film based on NPCS-CA and polyvinyl alcohol (PVA) incorporated with cinnamon essential oil (CEO) by the casting method. The chemical structure of the chitosan derivative was characterized by FT-IR, 1H NMR and XRD. Through the characterization of FT-IR, TGA, mechanical and barrier properties of the composite films, the optimal proportion of NPCS-CA/PVA was determined as 5/5. And, the tensile strength and elongation at break of the NPCS-CA/PVA (5/5) film with 0.4 % CEO were 20.32 MPa and 65.73 %, respectively. The results revealed that the NPCS-CA/PVA-CEO composite films exhibited an excellent ultraviolet barrier property at 200-300 nm and significantly reduced oxygen permeability, carbon dioxide permeability and water vapor permeability. Furthermore, the antibacterial property of film-forming solutions against E. coli, S. aureus, and C. lagenarium was distinctly improved with the increase of NPCS-CA/PVA proportion. And, the multifunctional films effectively extended the shelf-life of mangoes at 25 °C based on the characterization of surface changes and quality indexes. The NPCS-CA/PVA-CEO films could be developed as biocomposite food packaging material.

Preparation and wide band emission characteristics of Eu2+/Eu3+ co-doped Ba3P4O13 phosphors.

A series of phosphors Ba3P4O13:xEu2+/3+ (x = 0-0.1) were synthesized in a CO reduction atmosphere at a relatively low temperature (1113 K) by the solid-phase method. Crystallization and optical properties were investigated by using powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fluorescence spectrophotometry (PL/PLE), respectively. Under the excitation of 394 nm, the emission spectrum of the phosphor presents a broad spectrum band of Eu2+ and characteristic peaks of Eu3+ in the range of 400-750 nm, indicating the coexistence of Eu2+ and Eu3+ in the system. The occupation of Eu2+ and Eu3+ in the Ba3P4O13 matrix position was discussed by Gaussian fitting and PL spectra. The existence of energy transfer between Eu2+ → Eu3+ in the system can be found through PL spectra under excitation of 251 nm. The emission color of the phosphor can be adjusted by changing the Eu ion doping concentration, resulting in the CIE color coordinates changing from (0.213, 0.215) blue to (0.249, 0.261) light bluish white. The results show that Ba3P4O13:Eu2+/3+ phosphors can be used as a potential single-doped single-host white light-emitting material.

Site Occupancy Studies and Luminescence Properties of Emission Tunable Phosphors Ca9La(PO4)7:Re (Re = Ce3+, Eu2+).

The structure, site occupancies, and photoluminescence (PL) properties of Ce3+- or Eu2+-doped Ca9La(PO4)7 phosphors were investigated in this work. The powder X-ray diffraction (XRD) data and Rietveld refinement results showed that the phosphors are pure phases. The vacuum ultraviolet-ultraviolet-visible (VUV-UV-vis) spectra and decay curves confirmed that the Ce3+ and Eu2+ ions in Ca9La(PO4)7 occupied two crystal sites. Additionally, the tunable color can be obtained by adjusting doping concentration and altering temperature. The fabricated w-LED lamp based on Eu2+-doped Ca9La(PO4)7 phosphor gave properties with a color rendering index (CRI) of 85.26, CIE chromaticity coordinates of (0.358, 0.307), and color temperature (CCT) of 4329 K.

Optical properties of Eu2+ /Eu3+ mixed valence phosphor Ca2 SiO2 F2 :Eu2+ /Eu3.

The Eu2+ /Eu3+ mixed valence phosphor Ca2 SiO2 F2 :Eu2+ /Eu3+ was prepared using a solid-state reaction synthesis method in a CO atmosphere, and the optical properties were investigated. The spectroscopic properties revealed that Ca2+ ions were occupied by both Eu2+ and Eu3+ ions in Ca2 SiO2 F2 , and both ions were able to generate their characteristic emissions. A broad 5d â†’ 4f Eu2+ band at ~470 nm and narrow 4f â†’ 4f Eu3+ peaks upon excitation with n-UV light were observed. The ratio between Eu2+ and Eu3+ emissions changed regularly, and the relative intensity of the red component from Eu3+ became systematically stronger with increasing overall Eu content. As a result, the emission color of these phosphors can be tunable from blue to pink under n-UV light excitation.

Luminescence properties of Ce3+ in orthosilicate oxyapatite NaY9 (SiO4 )6 O2.

Ce3+ -doped orthosilicate oxyapatite NaY9 (SiO4 )6 O2 phosphors NaY9-x (SiO4 )6 O2 :xCe3+ were prepared by a conventional high-temperature solid-state reaction method, and their spectroscopic characteristics were systematically investigated. The occupancies of Ce3+ ions at two different sites (Wyckoff 6 h and 4f sites) in NaY9 (SiO4 )6 O2 were determined. The influence of doping concentration on the emission intensity of Ce3+ was investigated and the critical distance Rc was estimated in terms of the concentration quenching data.

Yellow-white emission of Ce3+ and Eu2+ doped Li2SrSiO4 under low-voltage electron-beam excitation.

Ce(3+) and Eu(2+) activated Li(2)SrSiO(4) phosphors were prepared using a high temperature solid-state reaction technique. The VUV-UV-vis photoluminescence (PL) of Ce(3+)-doped phosphors Li(2-x)Sr(1-x)Ce(x)SiO(4) and Eu(2+)-doped phosphors Li(2)Sr(1-x)Eu(x)SiO(4), the low-voltage cathodoluminescence (CL) of Eu(2+)-doped phosphor Li(2)Sr(0.991-x)Eu(0.009)SiO(4) and Ce(3+)-Eu(2+) co-doped phosphors Li(2-x)Sr(0.991-x)Eu(0.009)Ce(x)SiO(4) were measured and discussed in consideration of their potential application in field emission displays (FEDs). The intense emission of phosphors Li(2-x)Sr(0.991-x)Eu(0.009)Ce(x)SiO(4) is tunable in yellow to white color gamut under low-voltage cathode ray excitation.

Bright green-emitting, energy transfer and quantum cutting of Ba3Ln(PO4)3: Tb3+ (Ln = La, Gd) under VUV-UV excitation.

Tb3+ doped Ba3Gd(PO4)3 and Ba3La(PO4)3 phosphors were synthesized using the traditional high temperature solid state reaction method. The excitation, emission, and decay spectra were measured at room temperature. Efficient energy transfer (ET) from Gd3+ to Tb3+ exists in Tb3+ doped Ba3Gd(PO4)3, and the ET efficiency increases with the increase of Tb3+ concentration. The visible quantum cutting (QC) via cross relaxation was observed upon exciting low-spin (7D(J)) 5d levels of Tb3+ ions. Ba3Tb(PO4)3 sample shows relatively strong emission intensity in comparison with Zn2SiO4: Mn2+ (ZSM) upon 172 nm excitation, and with a decay time τ(1/10) about 6.4 ms under 351 nm excitation, indicating the potential application of this phosphor for plasma display panels (PDPs) and Hg-free lamps.

The quantum cutting of Tb(3+) in Ca(6)Ln(2)Na(2)(PO(4))(6)F(2) (Ln = Gd, La) under VUV-UV excitation: with and without Gd(3+).

The VUV-vis spectroscopic properties of Tb(3+) activated fluoro-apatite phosphors Ca(6)Ln(2-x)Tb(x)Na(2)(PO(4))(6)F(2) (Ln = Gd, La) were studied. The results show that phosphors Ca(6)Gd(2-x)Tb(x)Na(2)(PO(4))(6)F(2) with Gd(3+) ions as sensitizers have intense absorption in the VUV range. The emission color of both phosphors can be tuned from blue to green by changing the doping concentration of Tb(3+) under 172 nm excitation. The visible quantum cutting (QC) via cross relaxation between Tb(3+) ions was observed in cases with and without Gd(3+). Though QC can be realized in phosphors Ca(6)La(2-x)Tb(x)Na(2)(PO(4))(6)F(2), we found that Gd(3+)-containg phosphors have a higher QC efficiency, confirming that the Gd(3+) ion indeed plays an important role during the quantum cutting process. In addition, the energy transfer process from Gd(3+) to Tb(3+) as well as (5)D(3)-(5)D(4) cross relaxation was investigated and discussed in terms of luminescence spectra and decay curves.

Ca6Gd1.5Tb0.5Na2(PO4)6F2--an intense green-emitting phosphor under vacuum ultraviolet and low-voltage cathode ray excitation.

The investigations on photoluminescence and cathodoluminescence reveal that phosphor Ca(6)Gd(1.5)Tb(0.5)Na(2)(PO(4))(6)F(2) (CGPF-Tb) shows an intense green emission. Under the same conditions, the relative luminance of this phosphor is about 62%, 127%, and 71% of that of commercial phosphor Zn(2)SiO(4):Mn (ZSM) under 147 and 172 nm vacuum ultraviolet (VUV) light, and 2.5 kV/100 microA cm(-2) cathode ray excitation, respectively. A shorter luminescence decay time (tau(1/10) approximately 6.1 ms) makes it more suitable for displays application than ZSM. Hence CGPF-Tb is a promising candidate as a green-emitting component for applications in plasma display panels and field emission displays.