Light Emission from Gold Nanoparticles under Ultrafast Near-Infrared Excitation: Thermal Radiation, Inelastic Light Scattering, or Multiphoton Luminescence?

Abstract

Gold nanoparticles emit broad-band upconverted luminescence upon irradiation with pulsed infrared laser radiation. Although the phenomenon is widely observed, considerable disagreement still exists concerning the underlying physics, most notably over the applicability of concepts such as multiphoton absorption, inelastic scattering, and interband vs intraband electronic transitions. Here, we study single particles and small clusters of particles by employing a spectrally resolved power-law analysis of the irradiation-dependent emission as a sensitive probe of these physical models. Two regimes of emission are identified. At low irradiance levels of kW/cm, the emission follows a well-defined integer-exponent power law suggestive of a multiphoton process. However, at higher irradiance levels of several kW/cm, the nonlinearity exponent itself depends on the photon energy detected, a tell-tale signature of a radiating heated electron gas. We show that in this regime, the experiments are incompatible with both interband transitions and inelastic light scattering as the cause of the luminescence, whereas they are compatible with the notion of luminescence linked to intraband transitions.

Liquid Gallium Nanospheres Emitting White Light

“…More interestingly, the straight line can be extrapolated to the origin of the coordinate (see , Supporting Information). This is the unique feature of hot‐electron intraband luminescence observed previously in plasmonic hot spots and semiconductor NSs . This result indicates clearly that the broadband luminescence observed for the Ga NSs placed on the thin Ag film in the high excitation irradiance regime belongs to hot‐electron intraband luminescence, similar to blackbody radiation .…”

“…The lifetime derived from the luminescence decay was found to be shorter than 10 ps, which is beyond the time resolution of our instrument. Since the hot luminescence in this case is dominated by the intraband transition of hot electrons, it indicates the fast relaxation of hot electrons through emitting photons in the conduction band …”

“…This is the unique feature of hot-electron intraband luminescence observed previously in plasmonic hot spots and semiconductor NSs. [30,54,55] This result indicates clearly that the broadband luminescence observed for the Ga NSs placed on the thin Ag film in the high excitation irradiance regime belongs to hot-electron intraband luminescence, similar to blackbody radiation. [54,55] The emission patterns of the Ga NS recorded The dependence of the SHG intensity on the excitation irradiance is presented in the inset.…”

“…[30,54,55] This result indicates clearly that the broadband luminescence observed for the Ga NSs placed on the thin Ag film in the high excitation irradiance regime belongs to hot-electron intraband luminescence, similar to blackbody radiation. [54,55] The emission patterns of the Ga NS recorded The dependence of the SHG intensity on the excitation irradiance is presented in the inset. c) Nonlinear response spectra measured for a Ga NS with d ≈ 300 nm placed on a thin Ag film at different excitation irradiances (upper part).…”

“…Since the hot luminescence in this case is dominated by the intraband transition of hot electrons, it indicates the fast relaxation of hot electrons through emitting photons in the conduction band. [43,55] Laser Photonics Rev. 2019, 13, 1800214 C 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim…”