ABSTRACT
Four novel heterometallic RE-Na-organic frameworks, [(RE)Na3(PZTC)2(H2O)4]·2H2O (RE = Yb (1), Ho (2), Er (3), Y (4); PZTC = pyrazine-2,3,5-tricarboxylate), were synthesized via solvothermal reactions and characterized by IR, elemental analysis, and single-crystal X-ray diffraction. The results show that the four complexes are isostructural. In the frameworks, the trinuclear Na cluster and RE ion acting as nodes are bridged by the multifunctional PZTC ligand to give a 3-D framework. Codoping in the frameworks was realized due to their isostructural characteristics. The codoped complexes were calcinated at 800 °C to give rise to the corresponding oxides. Investigation of their photophysical properties shows that the upconversion luminescence (UCL) of the Ho system is green while that of the Er system is red upon excitation at 980 nm. With regard to the luminescence color and intensity, the Er system is preferable to the Ho system for application in bioimaging. Both the red and the green UCL of the Ho(3+) and Er(3+) systems involve a two-photon process. In addition, the UCL mechanism is given. The UCL comparison of Na-doped oxides with non-Na-doped oxides indicates that doping Na can greatly enhance the UCL of the Er system.
ABSTRACT
Four new three-dimensional isostructural lanthanide-cadmium metal-organic frameworks (Ln-Cd MOFs), [LnCd(2)(imdc)(2)(Ac)(H(2)O)(2) ]·H(2)O (Ln=Pr (1), Eu (2), Gd (3), and Tb (4); H(3)imdc=4,5-imidazoledicarboxylic acid; Ac=acetate), have been synthesized under hydrothermal conditions and characterized by IR, elemental analyses, inductively coupled plasma (ICP) analysis, and X-ray diffraction. Single-crystal X-ray diffraction shows that two Ln(III) ions are surrounded by four Cd(II) ions to form a heteronuclear building block. The blocks are further linked to form 3D Ln-Cd MOFs by the bridging imdc(3-) ligand. Furthermore, the left- and right-handed helices array alternatively in the lattice. Eu-Cd and Tb-Cd MOFs can emit characteristic red light with the Eu(III) ion and green light with the Tb(III) ion, respectively, while both Gd-Cd and Pr-Cd MOFs generate blue emission when they are excited. Different concentrations of Eu(3+) and Tb(3+) ions were co-doped into Gd-Cd/Pr-Cd MOFs, and tunable luminescence from yellow to white was achieved. White-light emission was obtained successfully by adjusting the excitation wavelength or the co-doping ratio of the co-doped Gd-Cd and Pr-Cd MOFs. These results show that the relative emission intensity of white light for Gd-Cd:Eu(3+),Tb(3+) MOFs is stronger than that of Pr-Cd:Eu(3+),Tb(3+) MOFs, which implies that the Gd complex is a better matrix than the Pr complex to obtain white-light emission materials.
ABSTRACT
Five novel 3D heterometallic lanthanide-zinc-organic frameworks, [H(H(2)O)(8)][LnZn(4)(imdc)(4)(Him)(4)] [Ln = La (1), Pr (2), Eu (3), Gd (4), Tb (5); H(3)imdc = 4,5-imidazoledicarboxylic acid; Him = imidazole], were synthesized via an in situ hydrothermal reaction, and tunable luminescence from yellow to white was obtained through the doping of Eu and Tb ions in the La-Zn framework.
