We have carried out a photoemission study using synchrotron radiation of dodecanethiolate-(DT-) passivated Au nanoparticles supported on the highly oriented pyrolytic graphite (HOPG) substrates. From detailed line-shape analyses of Au 4f core-level photoemission spectra of DT-passivated Au nanoparticles, it is found that Au 4f core-level spectra consist of the two components. We attribute these components to the inner Au atoms and surface Au atoms bonded to surface dodecanethiolates. From these results, we discuss the chemical states of the present DT-passivated Au nanoparticles.
We have carried out a photoemission study of dodecanethiolate-͑DT-͒ passivated Ag nanoparticles supported on the highly oriented pyrolytic graphite ͑HOPG͒ substrates. From detailed photoemission measurements, it is found that the Fermi-level onsets in the photoemission spectra of DT-passivated Ag nanoparticles on the HOPG substrates are not the metallic Fermi edge, with the steep slope being away from the Fermi level. We attribute the unusual spectral features in the vicinity of Fermi level to the dynamic final-state effect in photoemission, indicative of the interaction between the nanoparticle and substrate through the surface passivants on a femtosecond time scale.
). LMT and LZT substituted with 01 atom % of Mn with respect to Ti were synthesized by a polymerizable complex (PC) method.13 Titanium tetrabutoxide and nitrates of La, Mg, Zn, and Mn were used as raw materials. Citric acid and propylene glycol were also used as chelating and esterification reagents, respectively. The obtained precursors were fired at 1773 K for LMT:Mn 4+ , and at 1573 K for LZT:Mn 4+ for 2 h in air.SrTiO 3 :Mn 4+ (0.2 atom %) was also synthesized by the PC method for comparison. The obtained samples were characterized by X-ray diffraction analysis (XRD, Bruker AXS; D2 Phaser), diffuse reflectance spectroscopy in an ultraviolet visible region (UVvis DRS, Shimadzu; UV-3100) and PL spectroscopy at room temperature (Hitachi; F-4500 and JASCO; FP-6500). PL spectra at low temperature (10300 K) were also taken using a fluorescence spectrometer (Horiba; FluoroLog-3) with a cryostat. Excitation spectra were monitored for emission at 710 nm, whereas the emission spectra for LMT:Mn 4+ and LZT:Mn 4+ were taken with excitation at 340 and 360 nm, respectively. The band structures were determined by a density functional theory (DFT) using a CASTEP program.The XRD patterns indicated that the samples were obtained in a pure LMT or LZT phase with ordered B-site ( Figure S1). 14,15 No obvious changes in the peak intensity ratio and peak positions were seen with the substitution of Mn 4+ because the quantities of Mn 4+ substituted were very small (x = 0 1 atom %). When LZT was fired at 1673 K and higher temperature, La 2 TiO 5 of an impurity phase was formed accompanying with the volatilization of the Zn component. Therefore, the optimized firing temperature for LZT was 1573 K.
Tetravalent
manganese is known as one of the candidate luminous
centers to obtain red emission. There are still unclear factors in
Mn4+-activated oxide phosphors to achieve intense emission.
In this paper, we studied the photoluminescence properties of double
perovskite-type tantalates AE2LaTaO6 (AE = Ca,
Sr, and Ba) activated with Mn4+. All AE2LaTaO6:Mn exhibited Mn4+-emission in the deep red region
under excitation by near-ultraviolet-green light (300–570 nm)
at room temperature. Co-substitution of Mg2+, Al3+, and Ti4+ compensates unbalanced charge caused by oxygen
defects, resulting in the enhancement of Mn4+-emission.
The present cosubstitution effect is different from the usual cosubstitution,
such as the replacement of two Al3+ by Mn4+ and
Mg2+, taking into consideration the charge balance between
cations. Theoretical calculation of band structures based on density
functional theory suggests the presence of two kinds of quenching
schemes in AE2LaTaO6:Mn, photoionization and
electron transfer from valence band to t2g orbitals of
Mn.
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