Absorption Spectra Of Au Research Articles

Robust emission in near-infrared II of lanthanide nanoprobes conjugated with Au (LNPs-Au) for temperature sensing and controlled photothermal therapy

To address the poor activity and inaccurate in situ temperature measurements of composite photothermal probes, herein we report lanthanide nanoparticles-gold (LNPs-Au) nanoprobes for fluorescence temperature sensing and controlled photothermal therapy (PTT). The conjugation between LNPs and Au is done via electrostatic interactions. LNPs doped with rare earth cations (Yb3+, Ho3+, Er3+, and Ce3+) fluoresce strongly in the NIR-II region and their emission spectrum does not overlap with the absorption spectrum of Au. The intensities of LNPs-Au emission peaks at 1185 and 1560 nm highly depend on temperature, which is utilized in this study for the non-contact temperature measurements in the biologically relevant range. Deep tissue penetration of NIR-II radiation is observed, which is favorable for real-time temperature sensing. In addition, this radiation does not damage the normal tissue. Moreover, LNPs-Au nanoparticles reduce HeLa cell viability below 40 % and adequately inhibited tumor tissue in mice upon 808-nm irradiation. The results of this study will motivate the development of multifunctional photothermal probes for safer, controllable PTT of cancers with simultaneous temperature monitoring.

Rotating Au nanorod and nanowire driven by circularly polarized light.

The wavelength-dependent optical torques provided by a circularly polarized (CP) plane wave driving Au nanorod (NR) and nanowire (NW) to rotate constantly were studied theoretically. Using the multiple multipole method, the resultant torque in terms of Maxwell's stress tensor was analyzed. Numerical results show that the optical torque spectrum is in accordance with the absorption spectrum of Au NR/NW. Under the same fluence, the maximum optical torque occurs at the longitudinal surface plasmon resonance (LSPR) of Au NR/NW, accompanied by a severe plasmonic heating. The rotation direction of the light-driven NR/NW depends on the handedness of CP light. In contrast, the optical torque exerted on Au NR/NW illuminated by a linearly polarized light is null at LSPR. Due to the plasmonic effect, the optical torque on Au NR/NW by CP light is two orders of magnitude larger than that on a dielectric NR/NW of the same size. The steady-state rotation of NR/NW in water, resulting from the balance of optical torque and viscous torque, was also discussed. Our finding shed some light on manipulating a CP light-driven Au NR/NW as a rotating nanomotor for a variety of applications in optofluidics and biophysics.

Room temperature synthesis and optical studies on Ag and Au mixed nanocomposite polyvinylpyrrolidone polymer films

Optical properties of silver, gold and bimetallic (Au:Ag) nanocomposite polymer films which are prepared by chemical method have been reported. The experimental data was correlated with the theoretical calculations using Mie theory. We adopt small change in the theoretical calculations of bimetallic/mixed particle nanocomposite and the theory agrees well with the experimental data. Polyvinylpyrrolidone (PVP) was used as reducing and capping agent. Fourier transform infrared spectroscopy (FTIR) study reveals the presence of different functional groups, the possible mechanism that leads to the formation of nanoparticles by using PVP alone as reducing agent. Optical absorption spectra of Ag and Au nanocomposite polymers show a surface plasmon resonance (SPR) band around 430 and 532nm, respectively. Thermal annealing effect on the prepared samples at 60°C for different time durations result in shift of SPR band maximum and varies the full width at half maximum (FWHM). Absorption spectra of Au:Ag bimetallic films show bands at 412 and 547nm confirms the presence of Ag and Au nanoparticles in the composite.

Relativistic two-component formulation of time-dependent current-density functional theory: Application to the linear response of solids

In this paper we derive the relativistic two-component formulation of time-dependent current-density-functional theory. To arrive at a two-component current-density formulation we apply a Foldy-Wouthuysen-type transformation to the time-dependent four-component Dirac-Kohn-Sham equations of relativistic density-functional theory. The two-component Hamiltonian is obtained as a regular expansion which is gauge invariant at each order of approximation, and to zeroth order it represents the time-dependent version of the relativistic zeroth order regular Hamiltonian obtained by van Lenthe et al., for the ground state [J. Chem. Phys.99, 4597 (1993)]. The corresponding zeroth order regular expression for the density is unchanged, whereas the current-density operator now comprises a paramagnetic, a diamagnetic, and a spin contribution, similar to the Gordon decomposition of the Dirac four current. The zeroth order current density is directly related to the mean velocity corresponding to the zeroth order Hamiltonian. These density and current density operators satisfy the continuity equation. This zeroth order approximation is therefore consistent and physically realistic. By combining this formalism with the formulation of the linear response of solids within time-dependent current-density functional theory [Romaniello and de Boeij, Phys. Rev. B71, 155108 (2005)], we derive a method that can treat orbital and spin contributions to the response in a unified way. The effect of spin-orbit coupling can now be taken into account. As first test we apply the method to calculate the relativistic effects in the linear response of several metals and nonmetals to a macroscopic electric field. Treatment of spin-orbit coupling yields visible changes in the spectra: a smooth onset of the interband transitions in the absorption spectrum of Au, a sharp onset with peak at about 0.46 eV in the absorption spectrum of W, and a low-frequency doublet structure in the absorption spectra of ZnTe, CdTe, and HgTe in agreement with experimental results.

Absorption spectra and electronic structures of Au mAg n ( m + n = 8) clusters

The electronic structures and absorption spectra of Au m Ag n ( m + n = 8) clusters have been investigated using time-dependent density functional response theory. We have discovered that the vertical ionization potentials, highest occupied molecular orbital level, lowest unoccupied molecular orbital level and binding energies of the most stable binary Au m Ag n are intermediate between those of Ag 8 and Au 8 clusters. The analysis of the low-energy absorption spectra shows that the dominant excitation energies and the corresponding oscillator strengths exhibit an obvious odd–even oscillation with the variation of the number of Au atoms. The odd–even oscillation character indicates that the optical properties of Au m Ag n can be tuned by changing the stoichiometries. The excitation of electrons to exterior atoms plays a key role in optical responses of Au m Ag n clusters.

Microstructure and photoabsorption of Au/SiO2 nano-composite films

Au/SiO2 nano-composite multilayer thin films were prepared by magnetr on plasma sputtering. The microstructure, morphology and optical properties were investigated using transmission electron microscopy and absorption spectra. The Au particles dispersed in the SiO2 matrix of one single Au layer gre w with increasing deposition time in the initial time interval of less than 10s. No obvious change in the size of Au particles was observed in the films deposit ed for more than 10s, however, the shape of Au particles changed. The optical ab sorption peaks due to the surface plasma resonance appeared at a wavelength of 5 40—560nm for ［Au(t1)SiO2(600)］×5 thin films . The intensity of the absorption peak increased with increasing deposition time . Influence of the Au particle shape on the position and intensity of plasma res onance absorption peak was also discussed. The optical absorption spectra of Au/ SiO2 thin films are well in agreement with the theoretical optical ab sorption spectra calculated from reformed Maxwell-Garnett effective medium theor y.

Absorption Spectrum of Au I in the Vacuum Ultraviolet

The absorption spectrum of Au I, in the 960-2100 Å region, has been observed and analysed.The atomic vapours have been produced with both an induction heated furnace and with flash-pyrolysis.One hundred and thirty new lines have been observed, 101 of which have been classified in fifteen new series corresponding to transitions 5d106s 2S-5d96snp, nf and converging to the first four limits above the first ionization limit.Some of the remaining new lines have been interpreted as due to transitions from the metastable state and some other due to transitions of double-electron excitation.The relative value of the photoionization cross section has been measured in the 950-1350 Å region as well as the Fano parameters for the three strongest lines broadened by autoionization.

X-Ray M5 absorption limits of Au, Tl, Pb and Bi

Abstract The combination defects of the X-ray M 4 and M 5 absorption limits of Ta to Bi have been studied, and the energies of the absorption limits compared with the level energies obtained by XPS. The M 5 absorption spectra of Au, T1, Pb and Bi in the metallic state have been investigated carefully, and, as expected, a weak subsidiary absorption discontinuity found on the low energy side of the apparent M 5 absorption discontinuity in the respective spectra. Finally, it has been shown that the absorption limit on the subsidiary absorption discontinuity gives the true M 5 absorption limit for these elements.

Vaporization of elements for atomic absorption spectroscopy with capacitor discharge lamps

The thermal vaporization of elements for absorption spectroscopy has been accomplished without flames by heating fine filaments or thin strips of a solid in the optical path with an intense pulse of light from a capacitor discharge lamp. Kinetic absorption spectra were recorded photographically a short time afterward with a second flash of light used as a back-ground source. The absorption spectra of Au, B, Cu, Dy, Fe, Pb and W were produced directly from the solid element, Al and Eu from their chlorides deposited on thin graphite strips, and Ag, Al, Ca, Cu, Fe, Mg and Zn from impurities in W. Even though no quantitative analyses could be made, sensitivities seem to be in the low p.p.m. range. The method should be useful in the far ultraviolet as well as in the near ultraviolet and visible regions.