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Novel printing techniques for optical elements produce characteristics in these optical elements which can sometimes not be resolved with classic testing or imaging methods. As highly individualized components often have a significant cost associated with them, destructive methods are unwanted. For this work, Scanning Laser Optical Tomography (SLOT) is considered to overcome these challenges and provide knowledge and data which would otherwise not be accessible. SLOT is directly compared to µCT which is often the go-to imaging modality for small, printed optics. Advantages such as the possibility to measure fluorescence with volumetric resolution are presented in this work in the application of a functionalized silicone waveguide. Interactions between the excitation light and the sample are also measured in SLOT in form of absorption. The importance of absorption is highlighted with the example of a 3D printed glass block which has light refractive layers that are invisible in µCT measurements. SLOT should be considered as a quality control tool by scientists and manufactures of printed optical elements as it has many advantages over µCT.

Cryogels have morphological features that make them interesting for several applications such as catalysis, sensing or tissue engineering. Their interconnected network and open porous structure, build up by primary particles (such as inorganic nanocrystals or polymers), provide these materials with unique physical properties and high specific surface areas. While the library of cryogels is endless, widely used in the polymer chemistry field, in this review we will summarize the structure and properties, applications and challenges of inorganic nanocrystal-based cryogels obtained by freezing and freeze-drying an aqueous nanoparticle colloid. This fast, easy and versatile gelation method will be outlined, along with the corresponding macro-, micro- and nano-structures and gel morphologies that can be obtained, for example, by changing the freezing temperature or by using one nanoparticle system or nanoparticle mixtures. Their applications towards electrocatalysis, photocatalysis and photoelectrochemical sensing will be highlighted, as well as the challenges and prospects of these materials.

Optical silicones are suitable materials for different additive manufacturing techniques. Premixing uncured silicones with nanoparticles enables the manufacturing of functional materials useable as emitting or even deformation sensing materials. The incorporation of particles in different media is mainly controlled by their surface which can be modified by surface active agents. This modification is the main part of this work, while flexible waveguides are printed to prove the concept. As functional species luminescent quantum dots have gained significant attention due to their optical properties and precise control over shape and size. In this work cadmium selenide-cadmium sulfide core-shell quantum dots are used due to their strong emission and high photoluminescence quantum yield (PLQY). While these properties are well known and tunable, matrix stability and the associated hazard potential are still relatively unknown. This is determined by immersion tests on differently modified samples. Inductively coupled plasma optical emission spectrometry is used to quantify the leaked amount of cadmium.

In this work, nano-sized hard magnetic gallium-substituted iron oxide crystals, wherein gallium is used to stabilize the metastable epsilon iron oxide phase, were added to cement-water suspensions at different ratios, which were subsequently hydrated for at least 28 days. It is shown that higher contents of such nanocrystals in the hardened cement paste introduce a magnetic moment, whereas the mechanical properties remain unchanged compared to non-blended hardened cement paste for a wide concentration range.

The assembly of nanocrystals (NCs) into three-dimensional network structures is a recently established strategy to produce macroscopic materials with nanoscopic properties. These networks can be formed by the controlled destabilization of NC colloids and subsequent supercritical drying to obtain NC-based aerogels. Even though this strategy has been used for many different semiconductor NCs, the emission of NC-based aerogels is limited to the ultraviolet and visible and no near-infrared (NIR) emitting NC-based aerogels have been investigated in literature until now. In the present work we have optimized a gelation route of NIR emitting PbS and PbS/CdS quantum dots (QDs) by means of a recently established gel formation method using trivalent ions to induce the network formation. Thereby, depending on the surface ligands and QDs used the resulting network structure is different. We propose, that the ligand affinity to the nanocrystal surface plays an essential role during network formation, which is supported by theoretical calculations. The optical properties were investigated with a focus on their steady-state and time resolved photoluminescence (PL). Unlike in PbS/CdS aerogels, the absorption of PbS aerogels and their PL shift strongly. For all aerogels the PL lifetimes are reduced in comparison to those of the building blocks with this reduction being especially pronounced in the PbS aerogels.

In this work, the influence of two different types of cations on the 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 cross-linking, 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.

For a long time, researchers in nanochemistry have been exploring ways to create 3D structures using cross-linked nanoparticles, such as lyogels and aerogels. In the present work, how simple modifications to the nanoparticle surface can be used to influence the resulting structure in a targeted manner is demonstrated. Specifically, positively charged surface ligands containing amine groups are compared to negatively charged ligands typically used, containing carboxylic acid groups, to generate network structures using different gelation agents. By utilizing bridging through S2− ions, a network structure of anisotropic CdSe/CdS nanorods is generated, packing them side by side at the nanoscopic level. The resulting structures exhibit improved fluorescence properties comparable to those of tip-to-tip connected networks but without harsh conditions for the nanoparticle surfaces. This innovative new method of gelation using S2− ions can achieve adequate photoluminescence quantum yields as well as prolonged fluorescence lifetimes compared to other network structures.

Assemblies of colloidal nanoparticles (NPs) into various functional superstructures, such as ordered or nonordered, microscopic or macroscopic, and templated or self-supported, have recently attracted a lot of research interest. The continuous development of colloidal nanoparticle synthesis enables a fine-tuning of the structure and properties of such functional superstructures leading to numerous new applications. Herein, it is aimed to summarize a variety of assemblies based on ordered self-assembled NPs, e.g., stacked nanoplatelets, and nonordered self-assembled NPs, e.g., nanoparticle-based aerogels and cryoaerogels, systems ranging from the microscopic to the macroscopic range. Depending on the materials of the nanoparticle building blocks used, e.g., metallic, magnetic, semiconducting, or their combination in hybrid systems, both ordered and nonordered assemblies yield interesting properties for a wide variety of applications, such as catalysis, photocatalysis, or sensing, which are highlighted and discussed.

In this work, a new type of multicomponent nanostructures is introduced by forming interpenetrating networks of two different nanomaterials. In detail, gel networks from semiconductor nanorods are interpenetrated by Au nanowires. Two different types of gelling agents, namely S2− and Yb3+, are employed to trigger the network formation. The structural and electrochemical properties of the resulting materials are discussed. (Photo)electrochemical measurements are performed on the structures to compare the materials in terms of their conductivity as well as their efficiency in converting photonic energy to electrical energy. The new type of CdSe/CdS:Au nanostructure gelled with S2− shows one order of magnitude higher photocurrent than the system gelled with Yb3+. Moreover, the introduction of Au nanowires exhibit a photocurrent which is two orders of magnitudes higher than in samples without Au nanowires.

Since their discovery, cadmium chalcogenide nanoplatelets (NPLs) gained a lot of interest, not only due to their beneficial characteristic, but also because of their high affinity to self-assemble into ordered stacks. Interestingly, the stacks showed both the properties of the single NPLs and new collective features, such as charge carrier transport within the stacks. Until now, the stacking was, to the best of the knowledge, only performed in non-polar media mostly through the addition of antisolvents with higher polarity. Due to the fact, that many applications (e.g., photocatalysis) or procedures (such as gelation) occur in water, a route to self-assemble stacks directly in aqueous solution is needed. In this work a new synthesis route is thus introduced to produce stacks directly in aqueous media. The NPLs are phase transferred with mercaptocarboxylic acids to an aqueous KOH solution followed by an addition of less polar antisolvents to initialize the stacking (e.g., tetrahydrofuran). Furthermore, a mechanism of the stacking as well as four possible driving forces involved in the process are proposed supported by transmission electron microscopy, dynamic light scattering, infrared spectroscopy, and x-ray photoelectron spectroscopy measurements.

Destabilization of a ligand-stabilized semiconductor nanocrystal solution with an oxidizing agent can lead to a macroscopic highly porous self-supporting nanocrystal network entitled hydrogel, with good accessibility to the surface. The previously reported charge carrier delocalization beyond a single nanocrystal building block in such gels can extend the charge carrier mobility and make a photocatalytic reaction more probable. The synthesis of ligand-stabilized nanocrystals with specific physicochemical properties is possible, thanks to the advances in colloid chemistry made in the last decades. Combining the properties of these nanocrystals with the advantages of nanocrystal-based hydrogels will lead to novel materials with optimized photocatalytic properties. This work demonstrates that CdSe quantum dots, CdS nanorods, and CdSe/CdS dot-in-rod-shaped nanorods as nanocrystal-based hydrogels can exhibit a much higher hydrogen production rate compared to their ligand-stabilized nanocrystal solutions. The gel synthesis through controlled destabilization by ligand oxidation preserves the high surface-to-volume ratio, ensures the accessible surface area even in hole-trapping solutions and facilitates photocatalytic hydrogen production without a co-catalyst. Especially with such self-supporting networks of nanocrystals, the problem of colloidal (in)stability in photocatalysis is circumvented. X-ray photoelectron spectroscopy and photoelectrochemical measurements reveal the advantageous properties of the 3D networks for application in photocatalytic hydrogen production.