The metalorganic frameworks (MOFs) with lanthanides ions offer great potential in the optical area because can provide properties of flexibility, low density, low-cost methods of synthesis, and insolubility in water, which give them an advantage over traditional phosphors. In this study, a thenoyltriflouroacetone ligand (TTA) with a Tb 3+ MOF was synthesized (Tb = 10 and 50% mol) and its structural and luminescent properties were analyzed. The metalorganic compound was generated in a simple one-pot reaction from terbium nitrate and 2-thenoyltrifluoroacetone precursors at room temperature. By means of FTIR, it was confirmed the presence of carbon groups, which made possible the terbium ion chelation, and also the Tb-O bonds vibration modes. 1 HNMR results confirm that the complex with 10% mol of Tb 3+ contains three coordinates molecules of TTA and two waters molecules. The powders exhibit rod-like morphology with size about 170 nm of diameter and a length about 2 μm; the rod-like nature of powders was confirmed by SEM and TEM analyses. By XRD it was concluded that at higher terbium concentration (TTA-50Tb sample) higher the crystallite size and crystallinity, in fact the TTA-10Tb sample shows a partial-amorphous nature. By photoluminescence analyses, the 5 D4→ 7 FJ (J = 3, 4, 5 and 6) emissions were recorded for both synthesized samples (λexc = 376 nm). Furthermore, it was observed that the emission intensity was enhanced in a factor of 3.5 for the TTA-50Tb. The energy transfer efficiency from TTA to Tb 3+ (antenna effect) was 0.984 for TTA-10Tb and 0.993 for TTA-50Tb. Decay time analyses indicate effective lifetime of 1.45 and 1.60 m s for the samples doped at 10 and 50%, respectively, indicating that the forbidden transition rules are stronger at higher crystallinity. The integrated intensities of the 5 D4 → 7 F5 (green at 541 nm) and 5 D4 → 7 F6 (blue at 486 nm) emissions and their intensity ratios IG/IB upon 376 nm excitation have been evaluated for TTA-10Tb andTTA-50Tb samples. The CIE1931 color of the MOFs excited at 376 nm attains a higher green color purity by increasing the terbium concentration. This is in concordance with the increased IG/IB ratio up for the TTA-10Tb and TTA-50Tb samples. Thus, the TTA-50Tb sample exhibits a green color purity of 67.94% with chromaticity coordinates (0.30, 0.57), being very close to those (0.29, 0.60) of European Broadcasting Union illuminant green. This interesting feature of the TTA-50Tb sample, together with an experimental branching ratio of 61.3% for the 5 D4 → 7 F5 green emission, highlights its capability as solid state green laser pumped by GaN (376 nm) LEDs.

Abstract:The goal of this study was to generate a method to examine seasonal variability by climatic classification and Pacific seasonal factors to identify extreme wet and dry events in northern Mexico for the period 1952-2013. Using the standardized precipitation and evapotranspiration index (SPEI) on scales of three months (SPEI-3) and 24 months (SPEI-24), the variability of extreme wet and dry events were measured. The SPEI-3 and SPEI-24 anomalies were divided by the standard deviation (standardized Z anomalies). A Pearson correlation for SPEI-3, SPEI-24, Pacific decadal oscillation (PDO) and the oceanic El Niño index (ONI) was applied. Wet extreme events were recorded in

No abstract

This study presents a general method which can be used for the synthesis of mononuclear complexes with europium(III) and organic ligands with carboxylic groups. It describes the procedure for preparing a new mononuclear coordination complex with europium(III) and carboxylate ligands sourced from benzoic acid. The construction of mononuclear complexes with a coordination sphere saturated in carboxylic ligands must go through the preparation and purification of a europium(III) intermediate complex that presents a coordination sphere with anions that will be later exchanged for carboxylic groups and finally precipitated as a solvent-free or anion-free complex within the coordination sphere. The detailed synthesis procedure for powders of a new complex, as well as studies of its structural composition at each phase and luminescent properties, are detailed in this study. Analytical and spectroscopic data reveal the formation of a new mononuclear complex of the general formula [Eu(OOCC6H5)3·(HOOCC6H5)2]. The crystal structure of the Eu(III) complex was solved using X-ray powder diffraction data and EXPO2014 software, and the crystal structure result was deposited in the CCDC service with number 19771999.

No abstract