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Terbium doped calcium fluoride (CaF 2 :Tb3+) and cerium co-doped CaF 2 :Tb3+ (CaF 2 :Ce3+, Tb3+) nanoparticles were synthesized by the hydrothermal method by using citric acid (Cit) as surfactant. The as-synthesized nanoparticles have good dispersibility in water to form an aqueous transparent dispersion at a concentration of 20 mg/mL. The nanoparticles have the CaF 2 -type cubic structures. Photoluminescence (PL) investigation showed that energy transfer can be occurred effectively from Ce3+ ions to Tb3+ ions in Cit/CaF 2 : Ce3+, Tb3+ nanoparticles. And the PL intensity of Cit/CaF 2 : Ce3+, Tb3+ nanoparticles is very strong at a low concentration of 1 mg/mL, which is 16-fold as high as that of Cit/CaF 2 : Tb3+ nanoparticles. The strong green emission from Cit/CaF 2 : Ce3+, Tb3+ nanoparticles can selectively be quenched by Cu2+ ions in comparison to other metal ions and its detection limit is 1.02 × 10−5 M in an aqueous solution. The PL quenching is reversible by the addition of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) with the recovery of almost 80% of the original PL. The results revealed that Cit/CaF 2 : Ce3+, Tb3+ nanoparticles could find a promising application for the detection of Cu2+ ions in an aqueous solution. • CaF 2 :Tb3+ and CaF 2 :Ce3+, Tb3+ nanoparticles were synthesized by using Citrate as the surface modification. • The as-prepared nanoparticles formed a transparent aqueous dispersion with concentration up to 20 mg/mL. • Cit/CaF 2 : Ce3+, Tb3+ nanoparticles have strong green emission in an aqueous dispersion at a low concentration of 1 mg/mL. • Cit/CaF 2 : Ce3+, Tb3+ nanoparticles can selectively detect Cu2+ ions in water and detection limit is 1.02 × 10−5 M. [ABSTRACT FROM AUTHOR]

Perovskite compounds are always the focus in the material research field. Herein, the polycrystalline samples and single crystals of Na 2 ZrTeO 6 , a B-site ordered double-perovskite compound, were prepared successfully. Single crystal X-ray diffraction demonstrated that Na 2 ZrTeO 6 crystallizes in the cubic space group Fm-3m (No. 225) with unit parameters of a = b = c = 7.80360(10) Å. The crystal structure of Na 2 ZrTeO 6 , formed by ZrO 6 and TeO 6 octahedra through sharing the corner oxygen atoms, belongs to the typical rock-salt-type perovskite structure. The density functional theory calculations show that Na 2 ZrTeO 6 has a direct band gap with band gap of 3.21 eV, which is lower than the experimental value of 3.85 eV. Interestingly, the powder samples of Na 2 ZrTeO 6 exhibit a self-activated near-infrared emission centered at 780 nm under ultraviolet light excitation. And a strong luminescence thermal stability was also observed. Compared to room temperature, the luminescence intensity can maintain 64 % at 200 °C. [Display omitted] • The high-purity double-perovskite Na 2 ZrTeO 6 samples were synthesized by wet chemical method. • Structure analysis indicate that Na 2 ZrTeO 6 belongs to the typical rock-salt-type perovskite structure. • Na 2 ZrTeO 6 exhibits self-activated near-infrared emission centered at 780 nm excited by 308 nm. • The sample's emission intensity maintained 64 % of its room temperature peak intensity at 200 °C. [ABSTRACT FROM AUTHOR]

A new mixed-anion phosphate crystal Cs 2 Bi 2 Sr(P 2 O 7)(PO 4) 2 was obtained by molten salt method. Single-crystal X-ray diffraction data demonstrated that the compound crystallizes in monoclinic space group P 2 1 /c (No.14) with unit cell parameters a ​= ​17.708(10) Å, b ​= ​9.156(5) Å and c ​= ​9.221(5) Å, β ​= ​90.160(8) °. The structure exhibits a novel three-dimensional network, which is made up of BiO 6 , BiO 5 , SrO 6 and CsO 11 polyhedra sharing the corners with PO 4 tetrahedra and P 2 O 7 diphosphate groups. The band gap was estimated by the combined density functional theory and experimental study. Photoluminescence property of Cs 2 Bi 2- x Sr(P 2 O 7)(PO 4) 2 : x Eu3+ showed the excellent thermal stability and high quantum efficiency. The structure of a new mixed-anion phosphate Cs 2 Bi 2 Sr(P 2 O 7)(PO 4) 2 , belonging to a rare case with twinning structure, is herein reported. And the photoluminescence of Eu3+ doped Cs 2 Bi 2 Sr(P 2 O 7)(PO 4) 2 shows high quantum efficiency (92%). Image 1 • The structure of Cs 2 Bi 2 Sr(P 2 O 7)(PO 4) 2 (CBSP) exhibits rare twin structure. • The new CBSP crystals were firstly obtained using molten salt method. • The CBSP:0.25Eu3+ shows excellent thermal stability and high quantum efficiency. [ABSTRACT FROM AUTHOR]