Size-Dependent Ultrafast Electronic Energy Relaxation and Enhanced Fluorescence of Copper Nanoparticles

Abstract

The energy relaxation of the electrons in the conduction band of 12 and 30 nm diameter copper nanoparticles in colloidal solution was investigated using femtosecond time-resolved transient spectroscopy. Experimental results show that the hot electron energy relaxation is faster in 12 nm copper nanoparticles (0.37 ps) than that in 30 nm copper nanoparticles (0.51 ps), which is explained by the size-dependent electron-surface phonon coupling. Additional mechanisms involving trapping or energy transfer processes to the denser surface states (imperfection) in the smaller nanoparticles are needed to explain the relaxation rate in the 12 nm nanoparticles. The observed fluorescence quantum yield from these nanoparticles is found to be enhanced by roughly 5 orders of magnitude for the 30 nm nanoparticles and 4 orders of magnitude for the 12 nm nanoparticles (relative to bulk copper metal). The increase in the fluorescence quantum yield is attributed to the electromagnetic enhancement of the radiative recombination of the electrons in the s-p conduction band below the Fermi level with the holes in the d bands due to the strong surface plasmon oscillation in these nanoparticles.

Selektive dsDNA‐gesteuerte Bildung von Kupfer‐Nanopartikeln in Lösung

“…610 nm, l ex = 337 nm). [8] ] ! 100 mm ist das Fluoreszenzsignal, das aus der Metallisierung resultiert, gesättigt (Abbildung S2).…”

Laser-Based Formation of Copper Nanoparticles in Aqueous Solution: Optical Properties, Particle Size Distributions, and Formation Kinetics

“…[42] Finally, El-Sayed and coworkers show that CuNPs with diameters of 12 and 30 nm display nearly identical absorption spectra. [43] Therefore, although we do not expect the T-4Py spectral blue shift evident in Fig. 2 to be attributable to significantly smaller particle size distributions for CuNPs produced via LASiS in the presence of this tetrazolebased ligand, a determination of the CuNP particle size distributions is required as confirmation.…”

Fabrication of Nanoengineered Metallic Structures and Their Application to Nonlinear Photochemical Reactions

“…45 Plasmon resonance, which arises from the collective oscillation of conduction electrons, produces EM field enhancement effects in the vicinity of metallic nanoparticles. 46,47 When metallic nanoparticles are irradiated with light, the incident electrical field of the light induces coherent oscillation of the conduction electrons on the metallic surface. 29,47 The LSP resonant frequency is mainly determined by the electron density, the effective electron mass, and the size and shape of the charge distribution.…”

“…46,47 When metallic nanoparticles are irradiated with light, the incident electrical field of the light induces coherent oscillation of the conduction electrons on the metallic surface. 29,47 The LSP resonant frequency is mainly determined by the electron density, the effective electron mass, and the size and shape of the charge distribution. 48 Higher LSP resonance modes, such as quadrupole plasmon resonance, can also be excited when each half of the electron cloud moves parallel or antiparallel to the incident electric field.…”