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ZnO-ZnS-SiO2 composites were synthesized by an ultrasound-assisted Stöber method. The incorporation of blue-emitting ZnS on the surface of ZnO particles allowed the fabrication of a composite material with tunable emission. SEM pictures revealed star-shaped ZnO structures with a size about of 1 µm in length with multiple spindles. The composition of the materials was confirmed by EDS, FT-IR, and Raman spectroscopies. X-ray diffraction pattern analysis revealed that ZnO and ZnS have hexagonal wurtzite and cubic sphalerite crystal structures, respectively. The estimated band gap values of ZnS, ZnO, as well as the composites were 3.61, 3.13 and 3.21 eV, respectively. The emission spectrum of star-shaped ZnO exhibits a weak excitonic signal and a second intense and broad band centered around 620 nm. Photoluminescence analysis of the composites revealed a very broad emission band covering almost entirely the visible region of the spectrum and whose emission color ranges from orange to blue region of the CIE1931 chromaticity space, as the content of ZnS in the composite increases. Moreover, this tuning of the luminescence allows the generation of white light. [ABSTRACT FROM AUTHOR]

A series of the TeO2–GeO2–ZnO glass system was single and double doped with different Tb3+/Eu3+ ratios. Their luminescent and colorimetric properties were analyzed for possible use as phosphor materials in lighting devices. The characterization by X-ray diffraction and Raman spectroscopy verified the glassy nature of the fabricated samples. The luminescent properties of the doped glasses were analyzed by means of steady-state fluorescence and time-resolved spectroscopy. The Tb3+ excitation bands observed in the codoped samples while monitoring the 700 nm emission of Eu3+, as well as the shortening of Tb3+ lifetime in presence of europium indicated a Tb3+ → Eu3+ energy transfer, which main interaction type is electric dipole–dipole, according to Inokuti–Hirayama model. The Eu3+ → Tb3+ energy transfer also occurs in the samples but with lower efficiency. The CIE1931 chromaticity coordinates, upon different excitation wavelengths, show a multicolor tunning from green to orange-red due to the lanthanide concentration ratio and the Tb3+ → Eu3+ energy transfer process. [ABSTRACT FROM AUTHOR]

Hydrothermally grown SnO2 and SnO2:Eu nanoparticles of 4-11 nm size range were analyzed by photoluminescence (PL) and therrmoluminescence (TL) spectroscopy to study the effect of Eu-doping on their emission behaviors. It has been observed that most of the incorporated Eu3+ ions remain at the interstitial sites of SnO2 lattice. High Eu-contents in the nanoparticles generate lattice deformation, formation of Eu3+/Eu0 clusters at interstitial sites, or segregation to their surfaces. Formation of Eu clusters at interstitial sites enhances electronic defect density in the crystal lattice, reorganizes carrier trapping centers, and modifies their activation energies. Room temperature PL emission and beta-irradiated TL dose response of SnO2 nanoparticles enhance significantly when doped with 0.5 and 1.0 mol. % nominal of Eu3+, respectively, opening up their possibilities of applications in bio-imaging and radiation therapy. Possible mechanisms of enhanced PL and TL responses of the samples have been discussed. [ABSTRACT FROM AUTHOR]

2,4-Dinitrodiphenylamine (I), 2-nitro-4-(trifluoromethyl)aniline (II) and 4-bromo-2-nitroaniline (III) have been investigated by DFT and experimental FTIR, Raman and UV-Vis spectroscopies. The gas-phase molecular geometries were consistent with similar compounds already reported in the literature. From the vibrational analysis, the main functional groups were identified and their absorption bands were assigned. Some differences were found between the calculated and the experimental UV-Vis spectra. These differences were analyzed and explained in terms of the TD-DFT/B3LYP limitations, which were mainly attributed to charge-transfer (CT) effects. These findings were in agreement with previous works, which reported that TD-DFT/B3LYP calculations diverge from experimental results when the electronic transitions involve CT. Despite this, TD-DFT/B3LYP calculations provided satisfactory results and a detailed description of the electronic transitions involved in the absorption bands of the UV-Vis spectra. In terms of the NLO properties, it was found that compound (I) is a good candidate for NLO applications and deserves further study due to its good β values. However, the β values for compounds (II) and (III) were negatively affected compared to those found on o-nitroaniline., (Copyright © 2015 Elsevier B.V. All rights reserved.)