Counterintuitive thermo-optical response of metal-dielectric nanocomposite materials as a result of local electromagnetic field enhancement

Abstract

Thermo-optical properties of composite materials consisting of noble metal nanoparticles spread in a dielectric host matrix are relevant for various fields in fundamental and applied nanosciences. We present a calculation of these properties in the framework of the Maxwell-Garnett effective medium model, exemplified by the case of gold nanoparticles in silica. The spectral variations of bulk gold thermo-optical coefficients, including implicitly the temperature dependence of intra- and interband transitions, are first extracted from experimental results of the literature. The composite material effective thermo-optical coefficients are then determined, accounting also for particle and matrix volume thermal expansion as well as temperature dependence of the matrix refractive index. These calculations lead to counterintuitive results in the vicinity of the surface plasmon resonance of the nanoparticles, originating from the local electromagnetic field enhancement. The findings are used to simulate the temperature dependence of the optical absorption spectrum of a Au:glass composite material. The result is compared with experimental data from the literature with good agreement.