CdSe(core)/CdS(shell) nanorods (NRs) have been extensively investigated for their unique optical properties, such as high photoluminescence (PL) quantum efficiency (QE) and polarized light emission. The incorporation of these NRs in silica (SiO2) is of high interest, since this renders them processable in polar solvents while increasing their photochemical stability, which would be beneficial for their application in LEDs and as biolabels. We report the synthesis of highly luminescent silica-coated CdSe/CdS NRs, by using the reverse micelle method. The mechanism for the encapsulation of the NRs in silica is unravelled and shown to be strongly influenced by the NR shape and its asymmetry. This is attributed to both the different morphology and the different crystallographic nature of the facets terminating the opposite tips of the NRs. These results lead to the formation of a novel class of NR architectures, whose symmetry can be controlled by tuning the degree of coverage of the silica shell. Interestingly, the encapsulation of the NRs in silica leads to a remarkable increase in their photostability, while preserving their optical properties.

In this work, we present a method for the incorporation of anisotropic colloidal nanocrystals of many different shapes in silica in a highly controlled way. This method yields a uniform silica shell, with thickness tunable from 3 to 17 nm. The silica shell perfectly adapts to the shape of the nanocrystals, preserving their anisotropy, a crucial requisite for shape-dependent applications. Our method is based on an adaptation of the reverse microemulsion method. High control over the nucleation and growth of the shell is obtained by slowing down the hydrolysis and condensation rates of the silica precursor by lowering the ammonia concentration. This is shown to be essential for the formation of a uniform silica shell in the case of CdSe/CdS core/shell nanorods. Additionally, the general applicability of this method is demonstrated by coating different anisotropic semiconductor nanocrystals such as nanostars and 2D nanoplatelets. These results thus represent a crucial step toward the fabrication of highly processable and functionalized anisotropic nanoparticles.

a b s t r a c tLuminescent solar concentrators are low cost photovoltaic devices, which reduce the amount of necessary semiconductor material per unit area of a solar collector by means of concentration. The device is comprised a thin plastic plate in which luminescent species (fluorophores) have been incorporated. The fluorophores absorb the solar light and radiatively re-emit part of the energy. Total internal reflection traps most of the emitted light inside the plate and wave-guides it to a narrow side facet with a solar cell attached, where conversion into electricity occurs. The efficiency of such devices is as yet rather low, due to several loss mechanisms, of which self-absorption is of high importance. This work demonstrates that type-II semiconductor hetero-nanocrystals may offer a solution to the self-absorption problem in luminescent solar concentrators.

Due to the specific size‐dependent photoluminescence spectra of semiconductor nanocrystals (NCs), their use is promising as building blocks for new electronic and optical nanodevices such as light‐emitting diodes, solar cells, lasers and biological sensors. 1,2 In order to design these NCs with tailored properties for specific applications, a high level of control over their synthesis is of key importance. Therefore, it is of great importance to characterize both the shape as the composition of these systems. Here, a range of different colloidal semiconductor NCs are characterized using 2D and 3D electron microscopy techniques. We will discuss, 2D semiconductor CdSe nanoplatelets (NPLs), both flat as helical shaped 3 , which are investigated using electron microscopy techniques. The aim is to retrieve structural information using high resolution imaging which enables us to study the growth mechanism of these NPLs. The flat NPLs have mainly {100} edges (Figure 1.A) and only a thickness of 4 to 5 atomic layers (Figure 1.B). The analysis of the helical NPLs shows that they are zinc blende and that the helices are folded uniquely around the ⟨110⟩ axis (Figure 1.D). In order to retrieve the helicity of the ultrathin helical shaped platelets, electron tomography is applied. The three‐dimensional tomographic reconstructions confirm that the observed helices fully rotate over a diameter of ∼25 nm and that they are not preferentially left‐ or right‐handed (Figure 1.C). Furthermore, heteronanocrystals (HNCs) are studied as they improve the stability and, thereby, the surface passivation of the NCs when overgrown with a shell of a second semiconductor with a higher bandgap. In this manner, the robustness of the system and the photoluminescence quantum yield of the core is increased. 4 In order to understand the growth process of HNCs, both the 3D structure as the position of the core inside that structure is of key importance. We investigate two types of CdSe/CdS core/shell HNCs, with either a nanorod or bullet shape. High resolution HAADF‐STEM microscopy enables us to investigate the crystal structure of the core‐shell nanostructure (Figure 2.A,C). Advanced electron tomography based on novel reconstruction algorithms 5 is used to investigate the 3D shape and to reveal the position of the CdSe core in the CdS shell (Figure 2.B,D). For the CdSe/CdS core/shell bullets, the presence of two types of morphologies was revealed (Figure 2.D). High resolution STEM imaging was used to characterize the surface facets of both morphologies, which enabled us to compare the surface energy of both morphologies. For the CdSe/CdS nanorods, a sequential topotactic cation exchange pathway that yields CuInSe 2 /CuInS 2 nanorods with near‐infrared luminescence is further investigated 6 .