Search results for "ULTRAVIOLET"
showing 10 items of 853 documents
ZnO-latex hybrids obtained by polymer-controlled crystallization: a spectroscopic investigation.
2007
Micro- and submicrosized ZnO-polymer hybrid materials were synthesized by precipitating zinc oxide from an aqueous medium in the presence of poly(styrene-acrylic acid) latex nanoparticles, prepared by miniemulsion polymerization. Up to 10 wt % of the latex becomes incorporated into the crystals. Although the long-range order of the inorganic material is essentially not altered by the polymer, studies by photoluminescence (PL) spectroscopy and electron paramagnetic resonance (EPR) show that the latex particles influence the optical and paramagnetic properties of the hybrids, which can be correlated with changes in the defect structure. Typical PL emission spectra showed a narrow UV peak and …
ZnWO4 nanocrystals: synthesis, morphology, photoluminescence and photocatalytic properties
2018
The present joint experimental and theoretical work provides in-depth understanding on the morphology and structural, electronic, and optical properties of ZnWO4 nanocrystals. Monoclinic ZnWO4 nanocrystals were prepared at three different temperatures (140, 150, and 160 °C) by a microwave hydrothermal method. Then, the samples were investigated by X-ray diffraction with Rietveld refinement analysis, field-emission scanning electron microscopy, transmission electronic microscopy, micro-Raman and Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, and photoluminescence measurements. First-principles theoretical calculations within the framework of density functional the…
Visible-ultraviolet vibronic emission of silica nanoparticles
2014
We report the study of the visible-ultraviolet emission properties and the structural features of silica nanoparticles prepared through a laboratory sol-gel technique. Atomic force microscopy, Raman and Infrared investigations highlighted the 10 nm size, purity and porosity of the obtained nanoparticles. By using time resolved photoluminescence techniques in air and in a vacuum we were able to single out two contributions in the visible emission: the first, stable in both atmospheres, is a typical fast blue band centered around 2.8 eV; the second, only observed in a vacuum around the 3.0-3.5 eV range, is a vibrational progression with two phonon modes at 1370 cm(-1) and 360 cm(-1). By fully…
PBS Nanodots for Ultraviolet Radiation Nanosensor
2011
PbS nanodots embedded in a zirconium oxide nanofilm were explored as possible ultraviolet (UV) sensors for nanodosimetry purposes. The nanodots were excited by ultraviolet photons to get emission of weak electrons. The emitted charge correlated to UV exposure indicates that PbS nanodots have potential for use as UV sensors for nanodosimetry.
Toward Photopatternable Thin Film Optical Sensors Utilizing Reactive Polyphenylacetylenes
2013
Substituted polyphenylacetylenes featuring reactive pentafluorophenyl (PFP) ester moieties are synthesized. Parts of the reactive PFP groups are then converted with a mono ortho-nitrobenzyl-protected diamine in variable ratios. Thin films are prepared from these copolymers and irradiated with UV light (λ = 365 nm), resulting in crosslinking of the irradiated areas and hence enabling a photopatterning. We found that during the photocrosslinking process, the excess of PFP ester moieties is stable and remained intact, enabling a subsequent post-polymerization modification step with amines. Noteworthy, this subsequent modification with amines results in a dramatically shift in the UV-vis absorp…
Transition to Reinforced State by Percolating Domains of Intercalated Brush-Modified Cellulose Nanocrystals and Poly(butadiene) in Cross-Linked Compo…
2013
The classic nanocomposite approach aims at percolation of low fraction of exfoliated individual reinforcing nanoscale elements within a polymeric matrix. By contrast, many of the mechanically excellent biological nanocomposites involve self-assembled and space-filled structures of hard reinforcing and soft toughening domains, with high weight fraction of reinforcements. Here we inspect a new concept toward mimicking such structures by studying whether percolation of intercalated domains consisting of alternating rigid and reinforcing, and soft rubbery domains could allow a transition to a reinforced state. Toward that, we present the functionalization of rigid native cellulose nanocrystals …
Vacuum ultraviolet excitation of the 1.9-eV emission band related to nonbridging oxygen hole centers in silica
2004
Physical review / B 69, 153201 (2004). doi:10.1103/PhysRevB.69.153201
Laser-Fabricated Fluorescent, Ligand-Free Silicon Nanoparticles: Scale-up, Biosafety, and 3D Live Imaging of Zebrafish under Development
2022
This work rationalizes the scalable synthesis of ultrasmall, ligand-free silicon nanomaterials via liquid-phase pulsed laser ablation process using picosecond pulses at ultraviolet wavelengths. Results showed that the irradiation time drives hydrodynamic NP size. Isolated, monodisperse Si-NPs are obtained at high yield (72%) using post-treatment process. The obtained Si-NPs have an average size of 10 nm (not aggregated) and display photoemission in the green spectral range. We directly characterized the ligand-free Si-NPs in a vertebrate animal (zebrafish) and assessed their toxicity during the development. In vivo assay revealed that Si-NPs are found inside in all the early life stages of …
Silicon dioxide thin film luminescence in comparison with bulk silica
1998
Abstract The luminescence of the self-trapped exciton (STE) in SiO2 films was measured at low temperatures on the background of defect luminescence under cathodoexcitation and compared with bulk silica luminescence. The defect luminescence is mainly caused by non-bridging oxygen centers (a red luminescence band at 1.8 eV) and twofold coordinated silicon centers (blue and ultraviolet luminescence with 2.7 and 4.4 eV bands, respectively). The STE luminescence with a band at 2.3 eV is uniformly distributed within SiO2 film volume. Contrary to defect luminescence, whose intensity increases with irradiation time, the STE luminescence decreases almost to zero in a few seconds of irradiation time.…