Huan Jiao

Synthesis and photoluminescence of Mn4+ activated ternary-alkaline fluoride K2NaGaF6 red phosphor for warm-white LED application

A novel ternary-alkaline red emitting fluoride phosphor K2NaGaF6:Mn4+ was successfully synthesized through co-precipitation method. The crystal structure, morphology, electronic band structure and luminescence properties of K2NaGaF6:Mn4+ phosphors were investigated in details by using Rietveld refinement of X-ray diffraction data, scanning electron microscopy (SEM), density functional theory (DFT) calculation and different reaction parameters. The K2NaGaF6 host has a cubic unit cell with the space group Fmm and lattice parameters of a = 8.2577 (4) A, Z = 4, Vcell = 563.08 (8) A3. Under blue light excitation, Mn4+ activated K2NaGaF6 exhibits a bright narrow-band red emission. The PL properties of the K2NaGaF6:Mn4+ red phosphors were optimized with different Mn4+ concentrations and aging times. A warm-white LED device was fabricated using a blue LED chip combined with commercial yellow YAG:Ce3+ phosphor and synthesized K2NaGaF6:Mn4+ red phosphor. The color rendering index (CRI, Ra = 81.6) and corresponding color temperature (CCT = 3643 K) easily reached the commercial warm white light LED standards (Ra > 80 and CCT < 4000 K). All these results indicate that K2NaGaF6:Mn4+ phosphor would be a suitable red phosphor candidate for warm-white LED applications.

The structure, anion order, and Ce3+ luminescence of Y4Al2O9–Y4Si2O7N2 solid solutions

Oxonitridoalumosilicates Y4Al2−2xSi2xO9−2xN2x (0.00 ≤ x ≤ 1.00) were prepared and the substitution effect of [Al3+O2−] pairs by [Si4+N3−] pairs in Y4Al2O9–Y4Si2O7N2 solid solutions on the structure and its corresponding influence on the Ce3+ activated luminescence properties are investigated. Y4Al2−2xSi2xO9−2xN2x (0.00 ≤ x ≤ 1.00) shows two solid solution regions, x = 0.00–0.40 for solid solution I, x = 0.50–1.00 for solid solution II from X-ray and neutron diffraction analysis. In the solid solution I, the Ce3+ emission is mainly in the UV range with the maximum wavelength at 350 nm, and the intensity decreases rapidly with the increase of the N content. In the solid solution II, the Ce3+ doped samples show blue-green luminescence with the maximum wavelength at ∼450 nm and the wide excitation bands extend from UV to 450 nm. The phosphors in the solid solution II are promising candidates for white-LED applications.

Combination effect of ligands and ionic liquid components on the structure and properties of manganese metal–organic frameworks

Ionothermal reactions of 1,4-benzenedicarboxylic acid (H2BDC) and 4,4′-biphenyldicarboxylic (H2BPDC) with Mn(OAc)2 resulted in 12 compounds divided into four kinds of structural models: [RMI]2[Mn3(BDC)3X2] (1–5, type A), [EMI]2[Mn3(BPDC)4] (6, type B), [RMI]2[Mn2(BPDC)3(H2O)3] (7–9, type C) and [RMI]6[Mn9(BPDC)9(HBPDC)2(OAc)4] (10–12, type D). A combination effect of ligands and IL components can be observed in the structural construction, which also is reflected in the properties of thermal stability and fluorescence. The decomposition temperatures of Mn–BDC compounds are higher than those of Mn–BPDC compounds. The decomposition temperatures decrease with the alkyl chain in [RMI]+, due to a +I inductive effect. The maximum emissions of compounds 1–5 and 6–12 located at ca. 410 or 407 nm are assigned to ILCT of H2BDC and H2BPDC ligands, respectively.

Soft Template-Directed Reactions: One-Pot Synthetic Route for Bimetallic Core-Satellite-Shell Structured Electrocatalytic Nanospheres

A one‐pot synthesis strategy, which retards nanoparticle (NP) agglomeration in the initiation of reaction and prevents the combination of the core and small species, is reported. In the present study, we synthesize bimetallic core–shell structures of single Au cores and satellites‐like Pt NPs. The core was generated by using HAuCl4; thus, providing the unique conductive ability for electrons. The entire evolution process of Pt NPs during the whole reaction was confined within the SiO2 nanospheres. Through strong electrostatic attraction, the Pt NPs in a tight H3O+ packing accordingly increased the adsorbed hydrogen (Had) rate. The comparative investigation of electrocatalytic activities of the products and commercial Pt/C‐20 % in the hydrogen evolution reaction (HER) revealed that the Au@SiO2‐Pt, with a strong metal interaction effect in the electrolyte, exhibits a low Tafel slope of 52 mV dec−1, with its catalytic activity being maintained for at least 10 h. Impressively, it also demonstrates a high turnover frequency (TOF) value of 0.11 s−1.