Effects of chemical substitution on the structural and optical properties of α-Ag2-2xNixWO4 (0 ≤ x ≤ 0.08) solid solutions.

In this work, we investigated the effects of chemical substitution on the structural, electronic, and optical properties of α-Ag2-2xNixWO4 (0 ≤ x ≤ 0.08) solid solutions prepared by a facile microwave-assisted hydrothermal method. The results showed that the increase of Ni concentration in α-Ag2WO4 microcrystals as a host matrix caused a morphological transformation and a shift of the electronic and optical properties. Based on first principles calculations and using Wulff's construction, particle shapes and their transformations in α-Ag2WO4 and α-Ag2-2xNixWO4 can be affected by controlling the ratios of surface energy values between the different facets. In addition, theoretical calculations revealed that Ni substitution in α-Ag2WO4 is more favorable in the Ag2 and Ag4 positions, in which the local coordination of Ag atoms corresponds to clusters with coordination numbers of seven and four, respectively. This behavior could be related to the degree of medium-range structural disorder in α-Ag2-2xNixWO4 crystals. The experimental results were correlated with theoretical simulations to achieve a deeper understanding of the relationship between morphology and properties. These results provide the basis for a rational design for the compositional modulation of structural and optical properties.

The role of the Eu3+ concentration on the SrMoO4:Eu phosphor properties: synthesis, characterization and photophysical studies.

SrMoO(4) doped with rare earth are still scarce nowadays and have attracted great attention due to their applications as scintillating materials in electro-optical like solid-state lasers and optical fibers, for instance. In this work Sr(1-x)Eu(x)MoO(4) powders, where x=0.01; 0.03 and 0.05, were synthesized by Complex Polymerization (CP) Method. The structural and optical properties of the SrMoO(4):Eu(3+) were analyzed by powder X-ray diffraction patterns, Fourier Transform Infra-Red (FTIR), Raman Spectroscopy, and through Photoluminescent Measurements (PL). Only a crystalline scheelite-type phase was obtained when the powders were heat-treated at 800 °C for 2 h, 2θ=27.8° (100% peak). The excitation spectra of the SrMoO(4):Eu(3+) (λ(Em.)=614 nm) presented the characteristic band of the Eu(3+5)L(6) transition at 394 nm and a broad band at around 288 nm ascribed to the charge-transfer from the O (2p) state to the Mo (4d) one in the SrMoO(4) matrix. The emission spectra of the SrMoO(4):Eu(3+) powders (λ(Exc.)=394 and 288 nm) show the group of sharp emission bands among 523-554 nm and 578-699 nm, assigned to the (5)D(1)→(7)F(0,1 and 2) and (5)D(0)→(7)F(0,1,2,3 and 4), respectively. The band related to the (5)D(0)→(7)F(0) transition indicates the presence of Eu(3+) site without inversion center. This hypothesis is strengthened by the fact that the band referent to the (5)D(0)→(7)F(2) transition is the most intense in the emission spectra.

Synthesis and study of the photophysical properties of a new Eu3+ complex with 3-hydroxypicolinamide.

This work reports on the synthesis and characterization of a new complex of Eu(3+) with the 3-hydroxypicolinamide ligand (Hhpa). Here we present an approach for obtaining bis[2-carbamoyl(κO)pyridin-3-olato(κO')] lanthanide complexes, which were characterized through elemental analysis, thermal analysis, infrared and photoluminescence spectroscopies (emission, excitation, luminescence lifetimes, quantum efficiencies, Judd-Ofelt parameters and quantum yields). Although hpa can act as a bidentate ligand in different conformations, the results attest for the occurrence of a unique coordination site of low symmetry for the Eu(3+) ions, in which two anionic hpa ligands coordinate the cations through an O/O chelating system. The phosphorescence of the synthesized gadolinium complex provides the energy of the triplet state, which is determined to be at 20,830 cm(-1) over the ground state. This makes the Hhpa ligand very adequate for sensitizing the Eu(3+) luminescence, which leads to a very efficient antenna effect and opens a wide range of applications for the complex in light emitting organic-inorganic devices.

Photolumiscent properties of nanorods and nanoplates Y2O3:Eu3+.

Nanorods and nanoplates of Y(2)O(3):Eu(3+) powders were synthesized through the thermal decomposition of the Y(OH)(3) precursors using a microwave-hydrothermal method in a very short reaction time. These powders were analyzed by X-ray diffraction, field emission scanning electron microscopy, Fourrier transform Raman, as well as photoluminescence measurements. Based on these results, these materials presented nanoplates and nanorods morphologies. The broad emission band between 300 and 440 nm ascribed to the photoluminescence of Y(2)O(3) matrix shifts as the procedure used in the microwave-hydrothermal assisted method changes in the Y(2)O(3):Eu(3+) samples. The presence of Eu(3+) and the hydrothermal treatment time are responsible for the band shifts in Y(2)O(3):Eu(3+) powders, since in the pure Y(2)O(3) matrix this behavior was not observed. Y(2)O(3):Eu(3+) powders also show the characteristic Eu(3+) emission lines at 580, 591, 610, 651 and 695 nm, when excited at 393 nm. The most intense band at 610 nm is responsible for the Eu(3+) red emission in these materials, and the Eu(3+) lifetime for this transition presented a slight increase as the time used in the microwave-hydrothermal assisted method increases.

SiO2-Ag Composite as a Highly Virucidal Material: A Roadmap that Rapidly Eliminates SARS-CoV-2.

COVID-19, as the cause of a global pandemic, has resulted in lockdowns all over the world since early 2020. Both theoretical and experimental efforts are being made to find an effective treatment to suppress the virus, constituting the forefront of current global safety concerns and a significant burden on global economies. The development of innovative materials able to prevent the transmission, spread, and entry of COVID-19 pathogens into the human body is currently in the spotlight. The synthesis of these materials is, therefore, gaining momentum, as methods providing nontoxic and environmentally friendly procedures are in high demand. Here, a highly virucidal material constructed from SiO2-Ag composite immobilized in a polymeric matrix (ethyl vinyl acetate) is presented. The experimental results indicated that the as-fabricated samples exhibited high antibacterial activity towards Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as well as towards SARS-CoV-2. Based on the present results and radical scavenger experiments, we propose a possible mechanism to explain the enhancement of the biocidal activity. In the presence of O2 and H2O, the plasmon-assisted surface mechanism is the major reaction channel generating reactive oxygen species (ROS). We believe that the present strategy based on the plasmonic effect would be a significant contribution to the design and preparation of efficient biocidal materials. This fundamental research is a precedent for the design and application of adequate technology to the next-generation of antiviral surfaces to combat SARS-CoV-2.

On the photoluminescence behavior of samarium-doped strontium titanate nanostructures under UV light. A structural and electronic understanding.

A combined experimental and theoretical investigation on the photoluminescence properties of SrTiO(3) (ST) and SrSm(0.01)Ti(0.99)O(3) (ST_Sm) nanostructures is presented in this work. The nanocrystalline powders were prepared by the polymeric precursor method, and the order-disorder behavior of this material was investigated by means of X-ray diffraction (XRD), spectral absorbance (UV-vis), transmission electron microscopy (TEM) images, electron paramagnetic resonance (EPR) and photoluminescence (PL) experimental techniques. The decrease in the broad PL emission band of ST and ST_Sm powders measured at room temperature indicates an increase in the structural order as the annealing temperature increases, i.e. characteristic samarium peaks intensify as the structural order increases in ST_Sm samples. The interactions of the network clusters that form the ST and ST_Sm structures were evaluated by means of the ab initio periodic method at the density functional theory (DFT) level with the hybrid nonlocal B3LYP approximation. The symmetry-breaking process that leads to the presence of non-ideal [TiO(6)] and [SrO(12)] clusters, as well as the relationship between these clusters, provides favorable structural and electronic conditions for the appearance of PL phenomena.

Photophysical properties of new terbium (III) organophosphonates.

This paper reports on the synthesis, characterization and photophysical properties of the Tb3+ organophosphonates, TbH(O3PR)2, methylphosphonate (R = CH3), ethylphosphonate (R = C2H5), propylphosphonate (R = C3H7), and phenylphosphonate (R = C6H5). The layered Tb3+ organophosphonates were characterized by X-ray diffraction, IR spectroscopy, TG and elemental analysis. The interlayer distances of the Tb3+ organophosphonates evaluated by the X-ray diffractogram were 9.50 Angstrom for TbH(O3PCH3)2, 12.18 Angstrom for TbH(O3PC2H5)2, 14.84 Angstrom for TbH(O3PC3H7)2 and 15.20 Angstrom for TbH(O3PC6H5)2. The Tb3+ luminescence data revealed highly green emissive materials when they were excited at 368 nm, where the characteristic 5D4 --> 7FJ (J=6, 5, 4 and 3) transitions of Tb3+ were observed at 488, 543, 585 and 619 nm, respectively. The lifetime of the Tb(3+ 5)D4 --> 7F5 transition (lambda(exc)=368 nm and lambda(em)=543 nm) for the Tb3+ organophosphonates was evaluated from the decay curves, which values were of 2.88, 2.22, 2.14 and 2.59 ms, respectively for TbH(O3PCH3)2, TbH(O3PC2H5)2, TbH(O3PC3H7)2 and TbH(O3PC6H5)2. TG analysis revealed that these materials are thermally highly stable, with no water molecule in their composition, which makes them potential luminophores.