Shaozhe Lü

Second ligand-directed self-assembly of lanthanide(III) coordination polymers with 1,4-naphthalenedicarboxylate

Under hydrothermal conditions, 1,4-naphthalenedicarboxylic acid (H2NDC) reacts with lanthanide(III) chloride to form the coordination polymers [Ln2(NDC)3(H2O)2]·nH2O [n = 2, Ln = Eu (1); n = 1.5, Ln = Gd (2)]. If a second ligand, 4,4′-bipyridine (4,4′-bpy), is added to the reaction mixture, the coordination polymers [Ln2(NDC)3(4,4′-bpy)0.5(H2O)3]·(4,4′-bpy) [Ln = Eu (3); Ln = Yb (4)] are obtained. 1 and 2 are isostructural and they possess a porous 3D network with the lanthanide(III) ions bridged only by NDC anions. 3 and 4 are unprecedented lanthanide coordination polymers of polycarboxylate with 4,4′-bpy. They possess a 3D porous structure assembled by lanthanide ions with the linkers NDC and 4,4′-bpy, while lattice molecules of 4,4′-bpy are enclathrated in the cavities. The photophysical properties of 3 and the magnetic properties of 2 were investigated, and the thermogravimetric analyses of 1 and 3 were also carried out.

Hydrothermal Syntheses, Structures, and Properties of First Examples of Lanthanide(III) 2,3-Pyrazinedicarboxylates with Three-Dimensional Framework

Lanthanide 2,3-pyrazinedicarboxylate complexes with three-dimensional frameworks, [Ln(2)(pzdc)(3)(H2O)]x.2xH(2)O [Ln = Pr (2), Nd (3), and Eu (4)], were obtained by hydrothermal reactions of 2,3-pyrazinedicarboxylic acid (H(2)pzdc) and the lanthanide(III) chlorides, while [La-2(pzdc)(3)(H2O)](x).2xH(2)O (1) was obtained by hydro(solvo)thermal reaction of LaCl3.7H(2)O and 2,3-pyrazinedicarboxylic acid. They are isomorphous and exhibit complicated 3-D structures based on [Ln(2)(pzdc)(3)(H2O)] building blocks. In the asymmetric unit, the two Ln(3+) ions are both nine-coordinate, but with different coordination environments. The ligand pzdc coordinates to the central Ln(3+) ions in a tetradentate, hexadentate, or heptadentate manner. Utilizing the characteristic of Eu3+ ion to act as a conformational probe, we determined the high-resolution spectra of 4, which show that there are two Eu3+ ion sites in the coordination polymer. This is also in agreement with the results of the X-ray single-crystal diffraction study. It was concluded that there are two La3+, two Pr3+ and two Nd3+ ion sites in polymers 1, 2, and 3, respectively. The thermogravimetric analyses of these complexes show that all coordinated and uncoordinated water molecules were lost at the first weight loss above 240 C

Hydrothermal synthesis and upconversion luminescence properties of β-NaGdF4:Yb3+/Tm3+ and β-NaGdF4:Yb3+/Ho3+ submicron crystals with regular morphologies.

Single phase β-NaGdF(4):Yb(3+)/Tm(3+) and β-NaGdF(4):Yb(3+)/Ho(3+) submicron crystals with various morphologies including hexagonal prisms, spindles, and spheres were synthesized via the one-step hydrothermal method by controlling the pH values and sort of chelators (EDTA and citric acid). The prepared products showed intense up-converted luminescence (UCL) pumped by infrared laser at 980 nm. The hexagonal prisms that meaning high degree crystallinity demonstrated strong UCL in comparison with other morphologies such as spindles and spheres. In β-NaGdF(4):Yb(3+)/Tm(3+), UCL not only appeared transitions from (1)G(4), (1)D(2), and (1)I(6) states to the lower lying states of Tm(3+), but also (6)P(J)→(8)S(7/2) transition (310 nm) of Gd(3+). These UCL were responsible for three, five, and six photons processes determined by pump power dependence of UCL intensities. The observation of UCL of Gd(3+) implied occurrence of energy transfer from Tm(3+):(1)I(6) to Gd(3+):(6)P(J).

Structure and photophysical properties of europium complexes of succinamic acid and 1,10-phenanthroline

Abstract Two binuclear europium complexes [Eu2(SA)6(phen)2]·6H2O (1) and [Eu2(SA)4(phen)2(H2O)4](ClO4)3 (phenH)·H2O (2) (where SA=succinamate, phen=1,10-phenanthroline) have been synthesized and characterized by X-ray single crystal diffraction. For 1, the unit cell contains two crystallographically independent Eu(SA)3(phen) species in which the Eu3+ ions have two different coordination environments. Two types of binuclear molecule are arranged in different orientations in the crystal. The 7F0→5D0 excitation peaks at 580.16 and 580.46 nm at 77 K and the Stark components of 5D0→7FJ transitions, especially 5D0→7F1 and 5D0→7F2 emission lines, show that complex 1 has two Eu(III) ion sites, which is in good agreement with the results of the structure determination. In complex 2, four water molecules take the place of two bidentate chelating SA anions in the inner coordination sphere of 1. Outside the coordination sphere, the protonated phen molecule forms a hydrogen bond with a tridentate-coordinated carboxyl group and has a π–π stacking interaction with the coordinated phen molecule.

Transition to cubic phase and enhancement of green upconversion emission by adding La3+ ions in hexagonal NaLuF4:Yb3+/Er3+ nanocrystals

Phase transition from hexagonal to cubic was successfully achieved through La3+ ions tridoping in NaLuF4:Yb3+/Er3+ nanocrystals (NCs) by a solvothermal process at 300 °C. X-Ray diffraction (XRD) patterns, scanning electron microscopy (SEM) images, transmission electron microscopy (TEM) images, Fourier-transform infrared (FTIR) absorption spectra, upconversion (UC) luminescence spectra and decay curves were used to characterize the resulting samples. Compared to cubic phase α-NaLu0.78Yb0.2Er0.02F4 NCs which are similar in size and prepared at normal temperature (280 °C), the number of the surface organic groups such as hydroxyl group (–OH) attached on NaLu0.48La0.3Yb0.2Er0.02F4 NCs is reduced. Furthermore, the green UC emission increases and simultaneously the red UC emission decreases. The UC mechanisms were studied by power-intensity log dependence. It indicates that in both of the two samples, the red UC emission is a two-photon process when the excitation power density is low, but a three-photon process occurs when the excitation power density is high. However, the green UC emission is a two-photon process all the time both at low or high excitation power density. Through analyzing the luminescence decay curves of the 4S3/2 → 4I15/2 transition and 4F9/2 → 4I15/2 transition under the 980 nm excitation wavelength, it is concluded that the population of the 4F9/2 level originates from the 4I13/2 level, not from the 2H11/2/4S3/2 level in the two samples.

Solvothermal synthesis and upconversion properties of about 10 nm orthorhombic LuF3: Yb3+, Er3+ rectangular nanocrystals

The Yb(3+) and Er(3+) codoped orthorhombic LuF3 rectangular nanocrystals (NCs) with the size of about 10nm were synthesized by a facile and effective solvothermal process. X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), upconversion (UC) luminescence spectra and decay curves were used to characterize the resulting samples. Compared with YF3 and α-NaYF4 NCs, owning the similar size and the same doping levels of Yb(3+) ions and Er(3+) ions as LuF3 NCs, the green UC emission of LuF3 NCs is 18.7 times and 5.1 times stronger than that of YF3 and α-NaYF4 NCs respectively; the red UC emission of LuF3 NCs is 13.2 times and 0.6 times stronger than that of YF3 and α-NaYF4 NCs respectively. Under 980 nm wavelength excitation, the decay curves of both (4)S3/2→(4)I15/2 transition and (4)F9/2→(4)I15/2 transition exhibit a single exponential function, resulting from the fast energy migrations among Yb(3+) ions caused by the high concentration of Yb(3+) ions (20 mol%). Meanwhile, at relatively low power density, the slopes of the linear plots between log(I) and log(P) for green UC and red UC are 1.7 and 1.9 respectively, which are less than 2 due to the quenching of the thermal effect, indicating a two-photon process for them. At high power density, the slopes are decreased caused by the saturation effect. In addition, we proved the existence of the thermal effect by the pump power dependence of the intensity ratio of (2)H11/2→(4)I15/2 transition to (4)S3/2→(4)I15/2 transition.