Influence of the thickness of silica layer on the radiative relaxation of AuNR@SiO2 core–shell nanostructures upon photoexcitation

Silica-coated gold nanorods with different silica thicknesses (AuNR@X-SiO ₂ , X = 20, 35, 50 and 65, denoting the SiO ₂ thickness in nm on the longitudinal side) were excited with a 7-ns pulsed 1064-nm laser. The infrared emissions of AuNR@X-SiO ₂ , probed with a step-scan Fourier-transform interferometer, enveloped the optical phonon modes of the Si-O-Si bridge (1250–1000 cm ⁻¹ ) and adsorbed water (1700–1550 cm ⁻¹ ) within silica pores and minute blackbody radiation, indicating the capability of populating the optical phonon energy of capping layers in core-shelled nanostructures upon photoexcitation. The decay of the emission at 1250–1000 cm ⁻¹ was decelerated as the thickness of silica increased. The kinetic analysis on the emission evolutions provided the thermalization properties of SiO ₂ on a microsecond timescale, including the intrinsic spontaneous radiation and the non-radiative thermal conduction. The vibrational energy stored in the solid SiO ₂ and the embedded water might be capable of serving as an energy donor, that is, an optically-energized catalyst, for vibrationally-assisted chemical reactions.