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

Abstract

AbstractSilica‐coated gold nanorods with different silica thicknesses (AuNR@X‐SiO2, X = 20, 35, 50 and 65, denoting the SiO2 thickness in nm on the longitudinal side) were excited with a 7‐ns pulsed 1064‐nm laser. The infrared emissions of AuNR@X‐SiO2, 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 SiO2 on a microsecond timescale, including the intrinsic spontaneous radiation and the non‐radiative thermal conduction. The vibrational energy stored in the solid SiO2 and the embedded water might be capable of serving as an energy donor, that is, an optically‐energized catalyst, for vibrationally‐assisted chemical reactions.