IR‐to‐visible up‐conversion fluorescent nanocrystals of hexagonal‐phase NaYF4:20 %Yb,2 %Er and NaYF4:20 %Yb,2 %Tm have been synthesized by decomposition of multiprecursors of CF3COONa, (CF3COO)3Y, (CF3COO)3Yb, and (CF3COO)3Er/(CF3COO)3Tm in oleylamine at 330 °C. The average particle size is 10.5 ± 0.7 nm (from random measurements of 200 particles from five transmission electron microscopy images) and 11.1 ± 1.3 nm (from dynamic‐light‐scattering measurements). The up‐conversion fluorescence intensity of the hexagonal nanocrystals in this work is much higher than that of other cubic‐phase NaYF4:Yb,Er nanocrystals, including the ones in this work (by a factor of 7.5). Mechanisms for nucleation and growth of the hexagonal‐phase nanoparticles are proposed. These nanocrystals are easily dispersed in organic solvents, producing a transparent colloidal solution. The hydrophobic surfaces of the particles are made hydrophilic using a bipolar surfactant. These nanoparticles and their dispersions in various media have potential applications in optical nanodevices and bioprobes. 相似文献
Photodegradation of humic substances causes drastic changes in the UV–vis absorption and fluorescence properties of humic acids. In this study it is intended to fulfill the lack of knowledge about the spectral changes of humic acids during photocatalytic oxidation processes and elucidate the effects observed on the molecular size distribution of humic acid focusing on their analysis by UV–vis and fluorescence spectroscopy.
As confirmed by the spectroscopic evaluation of the molecular size distribution data, photocatalytic degradation of humic acid leads to the formation of lower molecular size (small fractions) and higher UV absorbing compounds. For fractions less than 10 kDa, UV254 absorbing moieties in treated humic acid samples become higher than that of raw humic acid designating the generation of new species during photocatalysis. UV–vis spectroscopic changes were also evaluated by the parameters relating to the concomitant removal of the total organic carbon as well as by the ratios using absorption values at discrete wavelengths. Moreover, the fluorescence spectra of treated humic acid samples show decreasing intensity profiles with increasing photocatalytic irradiation time. 相似文献
The pH mediated intra-molecular association and inter-molecular aggregation of a range of amphiphilic poly(l-lysine iso-phthalamide) polymers have been investigated in aqueous solution over a range of pH values and concentrations. The desired functionality of these novel bioresponsive amphiphilic polymers was achieved by incorporating pendant hydrophilic carboxyl groups along the polymer backbone, via the l-lysine moiety, balanced by a degree of hydrophobicity introduced via the iso-phthaloyl moiety. Incorporation of low levels of bis-functional Cy3 (poly-Cy3) and/or Cy5 dye (poly-Cy3/5 or poly-Cy5) co-monomers in the responsive polymer backbone allowed detailed probing of the pH mediated hydrophobic association using a combination of optical spectroscopic techniques. Both steady-state fluorescence spectroscopy and fluorescence lifetime measurements of poly-Cy3 revealed a conformational transition at pH 4.5. Thus, below a critical pH the polymer collapsed into a compact globular structure (hypercoil) bringing the fluorophore molecules into close proximity with one another. This resulted in a dramatic reduction in fluorescence intensity and fluorescent lifetime in the single fluorophore systems (poly-Cy3) accompanied by a red shift in the maximum emission wavelength. Observed redshifts in the emission maxima and enhancements of fluorescent lifetimes with increasing polymer concentration suggested the formation of polymer aggregates. Fluorescence resonance energy transfer (FRET) was measured in mixtures of single fluorophore containing poly-Cy3 (donor) and poly-Cy5 (acceptor) and dual fluorophore containing poly-Cy3 (donor)/Cy5 (acceptor) in an effort to distinguish between intra-molecular versus inter-molecular association. The relevance of the results with respect to potential in vivo applications (drug delivery and biodiagnostics) is discussed. 相似文献
Four novel non-ionic ethoxylated fatty alkyl amine surfactants (I–IV) were synthesised and investigated as corrosion inhibitors
of carbon steel in 1 M hydrochloric acid solution using gravimetric, open circuit potential and potentiostatic polarisation techniques. The percentage
inhibition efficiency (η%) for each inhibitor increased with increasing concentration until the critical micelle concentration
(cmc) was reached. The maximum inhibition efficiency approached 95.1% in the presence of 400 ppm of the inhibitor (IV). It
was found that the adsorption of the surfactants on carbon steel followed the Langmuir adsorption isotherm. Potentiostatic
polarisation data indicated that these surfactants act as mixed type inhibitors. The values of activation energy (Ea*) of carbon steel dissolution in 1 M HCl were calculated in the absence and presence of 400 ppm of each inhibitor. Finally, scanning electron microscopy (SEM)
was used to examine the surface morphology of polished carbon steel surfaces and those immersed in 1 M HCl in the absence and presence of 400 ppm of inhibitor (IV). 相似文献
Spectroscopic studies revealed that the compound [N,N′-di(quinoline-2-methylene) -1,2-phenylenediimine] (1) exhibited a rather high selectivity toward Zn2+ over other metal ions, even Cd2+. In acetonitrile, the red shift of fluorescent emission from 396 nm to 426 nm upon zinc binding is due to the formation of a 1:1 metal/ligand complex. 相似文献
A comprehensive study of the electronic absorption and emission spectra and the fluorescence quantum yield and lifetime of seven poly(di-n-alkylsilane)s and of three isotopically labelled poly(di-n-hexylsilane)s in hydrocarbon solution at room temperature is reported. Also reported are fluorescence polarization and carbon tetrachloride quenching of fluorescence of poly(di-n-hexylsilane). The observed fluorescence spectra, quantum yield, and polarization depend on the selected excitation energy in a very characteristic fashion, whereas the fluorescence lifetime does not; however, it depends on the selected emission energy. These characteristic dependencies are qualitatively accounted for by the previously proposed segment distribution model if one assumes that the photophysical behavior at higher excitation energies is strongly affected by the presence of a low-lying weakly allowed state in short-segment chromophores and the behavior at lower excitation energies is dictated by the selective excitation of emitting long-segment chromophores. 相似文献