In this work, mixing and co-gelation of Au nanoparticles (NPs) and highly luminescent CdSe/CdS core/shell nanorods (NRs) are used as tools to obtain noble metal particle-decorated macroscopic semiconductor gel networks. The hybrid nature of the macrostructures facilitates the control over the optical properties: while the holes are trapped in the CdSe cores, the connected CdSe/CdS NRs support the mobility of excited electrons throughout the porous, hyperbranched gel networks. Due to the presence of Au NPs in the mixed gels, electron trapping in the gold NPs leads to a suppressed radiative recombination, namely, quenches the fluorescence in certain fragments of the multicomponent gel. The extent of fluorescence quenching can be influenced by the quantity of the noble metal domains. The optical properties are monitored as a function of the NR:NP ratio of a model system CdSe/CdS:Au. By this correlation, it demonstrates that the spatial extent of quenching initiated by a single Au NP exceeds the dimensions of one NR, which the Au is connected to (with a length of 45.8 nm ± 4.1 nm) and can reach the number of nine NRs per Au NP, which roughly corresponds to 400 nm of total electron travel distance within the network structure.

Nanocrystal based networks are surrounded and reinforced by a continuous metal oxide shell.

The main aspect being, that interparticle connections essentially govern the properties in nanoparticle assemblies, thus, the control over nanocrystal connections is the main tool toward tailored gel structures. Manifold gelation techniques have been explored in the recent decade: via addition of oxidative agents, [3,5] cryogelation, [23,24] ion-induced, [25][26][27][28] or via light irradiation. [6,22,29] All gelation methods are based on the concept of overcoming the interparticle repulsion forces in a stable colloidal solution of nanocrystals facilitating their controlled assembly. The resulting structures are as different as their methods, but overall they still deliver structures with large surface areas, low densities, high and open porosity. These properties unite all these structures, even if they differ greatly in their composition and the interaction between the building blocks. Especially in case of nanoparticle assemblies consisting of two or more different components (in the following named heteroassemblies), the connection itself between the particles has a great impact on the optical properties evolving in the gel networks, e.g., spatial separation of photoexcited charge carriers. [30][31][32][33] In the present work, we give an insight into the importance of choosing the most suitable gelation agent for specific purposes requiring different gel morphologies. As recent studies have mostly dealt with ion-induced gelation of In this work, the influence of two different types of cations onthe gel formation and structure of mixed gel networks comprised of semiconductor (namely CdSe/CdS nanorods NR) and Au nanoparticles (NP) as well as on the respective monocomponent gels is investigated. Heteroassemblies built from colloidal building blocks are usually prepared by ligand removal or crosslinking, thus, both the surface chemistry and the destabilising agent play an essential role in the gelation process. Due to the diversity of the composition, morphology, and optical properties of the nanoparticles, a versatile route to fabricate functional heteroassemblies is of great demand. In the present work, the optics, morphology, and gelation mechanism of pure semiconductor and noble metal as well as their mixed nanoparticle gel networks are revealed. The influence of the gelation agents (bivalent and trivalent cations) on the structure-property correlation is elucidated by photoluminescence, X-ray photoelectron spectroscopy, and electron microscopy measurements. The selection of cations drastically influences the nano-and microstructure of the prepared gel network structures driven by the affinity of the cations to the ligands and the nanoparticle surface. This gelation technique provides a new platform to control the formation of porous assemblies based on semiconductor and metal nanoparticles.