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

Abstract

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 À1 ) and adsorbed water (1700-1550 cm À1 ) within silica pores and minute blackbody radiation, indicating the capability of populating the optical phonon energy of capping layers in coreshelled nanostructures upon photoexcitation. The decay of the emission at 1250-1000 cm À1 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 nonradiative 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. K E Y W O R D Sinfrared emission, photothermal effect, silica-coated gold nanorod, step-scan FTIR Jhih-Jie Lai and Meng-Chen Shih contributed equally to this work.