Silica aerogels as hosting matrices for WS₂ nanotubes and their optical characterization

Due to their high porosity, aerogels can be efficiently used as host matrices for functional materials. The solid matrix is advantageous over liquid suspensions because it maintains the nanoparticles static and inhibits agglomeration and precipitation. The current paper reports on the controlled addition of less than 0.1 wt% of WS₂ nanotubes (WS₂ NTs) to aerogels, retaining the aerogel’s mesoporous structure, and demonstrates how increasing nanotubes’ concentration influences the optical properties of the composite aerogel. The absorption spectrum of WS₂ NTs consists of two peaks, attributed to the direct gap transition and referred to as excitons A and B and is preserved in the aerogel. WS₂ NTs’ extinction spectrum, on the other hand, is dominated by exciton–polaritons and is modified in the aerogel, with respect to the NTs dispersed in liquid. This occurs due to scattering effects, resulting in broadening with increased NT content, washing out the excitonic transitions. Furthermore, femtosecond optical pump–probe measurements carried out on NTs dispersed in both ethanol and the silica aerogel suggest that the electronic processes underlying the overall optical behaviour of the nanotubes, and hence also their optoelectronic and photochemical properties are preserved in the aerogel matrix. These findings make the obtained nanocomposites interesting for use in modern optical and optoelectronic devices.