No abstract

In, out, shake it all about: The distribution of fluorescence‐labeled amino groups on mesoporous silica was imaged by confocal laser scanning microscopy. The mobility of the aminosilane precursor determines the degree of external vs. pore‐surface functionalization. This observation was used to develop a simple and general method for the modification of external mesoporous silica surfaces.

The effect of water on the reaction of 3-aminopropyltriethoxysilane (APTES) with mesoporous silica is investigated on two model systems. A MCM-41type material with a well-defined pore size is used to investigate changes in the pore size distribution upon reaction with APTES in toluene containing various amounts of water. It is found that, with increasing amount of water, clustering of APTES occurs, leading to a nonuniform distribution of the grafted amino groups and a scarcely functionalized pore body. A second model system with defined particle morphology and one-dimensional channels is employed to visualize the distribution of the grafted amino groups by fluorescent labeling and confocal laser scanning microscopy. The combination of nitrogen sorption and confocal laser scanning microscopy provides valuable insights concerning the role of trace water in the functionalization of mesoporous silica with alkoxysilanes. SECTION Nanoparticles and Nanostructures

SrAl 2 O 4 doped with europium and dysprosium is a powerful and widely used afterglow material. Within this material strontium is found in two crystallographic different sites. Due to the similar ion radii and same charge, Eu 2+ -ions can occupy both sites, resulting in two different Eu 2+ -ions, one emitting in the blue and one in the green spectral range. The blue emission is thermally quenched at room temperature. In this paper we investigate the energy transfer between different Eu ions depending on the concentration and temperature using two different approaches: lifetime measurements and integrated intensity. We find an activation energy for the thermal quenching of the blue emission of 0.195 ± 0.023 eV and a critical radius for the energy transfer of 3.0 ± 0.5 nm. These results can help in designing better afterglow materials due to the fact that with energy transfer parts of the lost emission in the blue region at room temperature can be converted to the green site.

Glow-in-the-dark materials have been around for a long time. While formerly materials had to be mixed with radioactive elements to achieve a sufficiently long and bright afterglow, these have now been replaced by much safer alternatives. Notably strontium aluminate, SrAl 2 O 4 , doped with europium and dysprosium, has been discovered over two decades ago and since then the phosphor has transcended its popular use in watch dials, safety signage, or toys with more niche applications such as stress sensing, photocatalysis, medical imaging, or flicker-free light-emitting diodes. A lot of research efforts are focused on further improving the storage capacity of SrAl 2 O 4 :Eu 2+ ,Dy 3+ , including in nanosized particles, and on finding the underlying physical mechanism to fully explain the afterglow in this material and related compounds. Here an overview of the most important results from the research on SrAl 2 O 4 :Eu 2+ ,Dy 3+ is presented and different models and the underlying physics are discussed to explain the trapping mechanism at play in these materials.