Radiative Cooling of Surface-Modified Gold Nanorods upon Pulsed Infrared Photoexcitation

Abstract

Transient infrared emissions of gold nanorods capped with various materials (AuNR@X, X = CTAB, PSS, mPEG, and SiO) upon ∼70-μs pulsed 1064 nm excitation of their longitudinal surface plasmonic bands were collected with a time-resolved step-scan Fourier-transform spectrometer. Comparing the observed emission contours with the blackbody radiation spectra revealed that parts of the additional emission intensity at low wavenumbers (1300-1000 cm) were attributed to the vibrational modes of the capping materials, suggesting that the photothermal energy of AuNRs can be thermalized not only via blackbody radiation but also via radiative and nonradiative processes of the capping materials. In addition, the infrared emission of AuNR@SiO was more prolonged (∼1 ms) than those of the other three (∼300 μs). The photothermal energy can be efficiently randomized to the internal degrees of freedom of the soft molecular capping materials but can be stored by the rigid ones, for example, SiO, followed by extended radiative cooling.

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

“…The data acquisition followed previous reports [13,14] with slight modifications. The AuNR@X-SiO 2 sample dried on the CaF 2 window mentioned in Section 2.1.5 was mounted at the focal point of the parabolic mirror for collecting the external emission at the side of the interferometer.…”

“…Porous silica-coated plasmonic metal nanoparticles have numerous advantages in dispersivity and in chemical and thermal stability. [12] Recent studies have shown that optically-heated gold nanostructures are capable of radiatively relaxing energy via the thermal emission of the infrared photons [13,14] rather than thermal conduction. The thermalization kinetics depends on the types of the capping materials.…”

“…The thermalization kinetics depends on the types of the capping materials. [14] The coating layer of SiO 2 prolongs the evolution of the infrared emission. [14] In this work, the radiative relaxation of gold nanorods coated with different thicknesses of SiO 2 , named AuNR@X-SiO 2 (where X denotes the thickness of the SiO 2 layer in nm on the longitudinal side), were probed with a step-scan Fourier-transform spectrometer upon nanosecond excitation.…”

“…[14] The coating layer of SiO 2 prolongs the evolution of the infrared emission. [14] In this work, the radiative relaxation of gold nanorods coated with different thicknesses of SiO 2 , named AuNR@X-SiO 2 (where X denotes the thickness of the SiO 2 layer in nm on the longitudinal side), were probed with a step-scan Fourier-transform spectrometer upon nanosecond excitation. Within the laser pulse duration of nanoseconds, the core AuNR and the SiO 2 shell can be treated at thermal equilibrium.…”

“…AuNR@CTAB was prepared using the seed-growth method with minor modifications. [14,16] Solution A contained 0.36 g of cetyltrimethylammonium bromide (CTAB) dissolved in 10.0 ml of deionized water and 172 μl of 0.029 M chloroauric acid (HAuCl 4 ). Solution B was prepared in an ice bath by mixing 5.0 ml of 0.02 M sodium borohydride (NaBH 4 ) and 5.0 ml of 0.02 M sodium hydroxide (NaOH).…”