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Aerogels can bridge the nanoscopic to the macroscopic world. One physical phenomenon typically limited to the nanoscopic world is the occurrence of localized surface plasmon resonances (LSPRs), which are observed in conductive nanoparticles. Once brought into close contact, assemblies or superstructures of these nanoparticles often lose their plasmonic properties in the transition stage towards the bulk material. Therefore, LSPRs are typically not observed in macroscopic objects. The present work aims at voluminous nanoparticle-based aerogels with optical properties close to that of the initial colloidal solution and the possibility to manipulate the final plasmonic properties by bringing the particles into defined distances. In detail, Ag nanocrystals with silica shells ranging from 0 to 12 nm are employed as building blocks, which are assembled from their solution into macroscopic three-dimensional superstructures by freezing and subsequent lyophilization. These cryogelated aerogels are synthesized as monoliths and thin films in which the Ag nanocrystals are arranged in defined distances according to their silica shell. The resulting aerogels exhibit plasmonic properties ranging from a behavior similar to that of the building blocks for the thickest shell to a heavily distorted behavior for bare Ag nanocrystals.

In this article, we demonstrate the fabrication of tailored multicomponent cryoaerogels from colloidal nanoparticles via the cryogelation method. With this method, it is possible to control the amount of components very precisely. Furthermore, the microscopic distribution of the different nanoparticle components in the resulting monolithic structure is shown to be adjustable by simply mixing calculated amounts of colloidal nanoparticle solutions with a suitable surface charge. We focus on titania cryoaerogels due to their potential for optical applications and investigate the properties of synthesized titania-gold cryoaerogels in dependency of the composition. In addition, titania-platinum cryoaerogels were tested for photocatalytic applications such as hydrogen evolution and showed a significant increase in performance and stability compared to their respective colloidal solutions. While showing comparable results for hydrogen evolution with aerogels as reported in literature, the fabrication is much faster and less complex and therefore might enable future industrial application.

We address optical amplification properties of quantum nanoparticles of the cadmium selenide/cadmium sulfide (CdSe/CdS) material system with different dimensionality of spatial confinement. CdSe/CdS core/shell quantum dots (QDs), core/shell quantum rods (QRs) and 5 monolayer thick core/crown nanoplatelets (NPLs) at ambient temperature are considered, exhibiting 0D, 1D and 2D spatial confinement dimensionality of the electronic system, respectively. Continuous films of all these nanoparticles are synthesised, and amplified spontaneous emission (ASE) spectra are measured under femtosecond pumping at wavelengths of 400 nm and 800 nm, respectively. The lowest threshold is found for NPLs and the highest for QDs, demonstrating the influence of the rod-like and plate-like CdS structures. To emphasize this effect, ASE is demonstrated also in CdSe/CdS QRs and NPLs under nanosecond pumping at 355 nm in the same material films. The amplification has been achieved without use of any feedback structure, emphazising the efficiency of the antenna effect. The pumping threshold fluences for NPLs and QRs are observed to be similar, but no ASE is observed in QDs up to the damage threshold of the nanoparticle layers. The length variation investigation with nanosecond pumping resulted in the gain coefficients of 29 cm -1 and 37 cm -1 for QRs and NPLs, respectively.

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In this work, luminescent CdSe@CdS dot-in-rod nanocrystals, CdSe@CdS/ZnS nanorods as well as CdSe–CdS core–crown nanoplatelets were transferred into aqueous phase via ligand exchange reactions. For this purpose, bifunctional thiol-based ligands were employed, namely mercaptoacetic acid (MAA), 3-mercaptopropionic acid (MPA), 11-mercaptoundecanoic acid (MUA) as well as 2-(dimethylamino)ethanthiol (DMAET). Systematic investigations by means of photoluminescence quantum yield measurements as well as photoluminescence decay measurements have shown that the luminescence properties of the transferred nanostructures are affected by hole traps (induced by the thiol ligands themselves) as well as by spatial insulation and passivation against the environment. The influence of the tips of the nanorods on the luminescence is, however, insignificant. Accordingly, different ligands yield optimum results for different nanoparticle samples, mainly depending on the inorganic passivation of the respective samples. In case of CdSe@CdS nanorods, the highest emission intensities have been obtained by using short-chain ligands for the transfer preserving more than 50% of the pristine quantum yield of the hydrophobic nanorods. As opposed to this, the best possible quantum efficiency for the CdSe@CdS/ZnS nanorods has been achieved via MUA. The gained knowledge could be applied to transfer for the first time 2-dimensional CdSe–CdS core–crown nanoplatelets into water while preserving significant photoluminescence (up to 12% quantum efficiency).