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The synthesis of well-defined oxide nanocrystals (NCs) with high crystallinity and ultra-small size (typically below 5 nm) is extremely challenging in view of their numerous important related applications. Often the obtained products suffer from particle aggregation, hindering beneficial advantages of nano-size character such as low light scattering properties. Solvothermal methods are very powerful synthetic approaches toward such nanocrystals especially when polyols are used as solvents. Their unique properties and gradual changes in a homologous series of polyols provide a wide range of tools for reaction design. A prominent example of such a reaction is the glycothermal synthesis of Y3Al5O12 (YAG) in 1,4-butanediol in which 20 nm aggregated nanoparticles can be obtained. Herein, we introduce a key evolution of YAG:Ce nanoparticles prepared via a modified glycothermal approach. We emphasize the crucial role of the co-solvent together with the amount of water. Addition of DEG and dehydration of precursors lead to 4 nm non-aggregated nanocrystals with high crystallinity and the correspondingly high photoluminescence emission. Very clear and stable colloidal solutions with concentrations of nanocrystals up to 50% are obtained. The prepared colloids are directly used for the fabrication of homogenous, luminescent and crack-free thin films without the addition of any plasticisers or surfactants. The thickness of the films is simply and efficiently controlled by the concentration of the colloidal solution. [ABSTRACT FROM AUTHOR]

Silica-based hybrid materials doped with gold nanoparticles (AuNPs) of different shapes were prepared with an adapted sol–gel technology (using MTEOS) and polished to high optical quality. Both spherical (23 and 45 nm in diameter) and bipyramidal (36, 50 and 78 nm in length) AuNPs were prepared and used as dopants. The AuNPs were functionalized with a novel silicone polymer for compatibilization with the sol–gel medium. The glass materials showed well defined localized surface plasmon resonance (SPR) absorbance from the visible to NIR. No redshifts in the spectra, due to the increase in doping concentration, were observed in the glasses, proving that no or very small SPR coupling effects occur. Spectroscopic Muller Matrix Ellipsometry showed that the shorter bipyramidal AuNPs (36 and 50 nm in length) have a clear preferred orientation in the MTEOS matrix, i.e. a tendency to be oriented with their long axis in the plane parallel to the glass surfaces. Dispersions of AuNPs have proven to be good optical power limiters that depend on particle size and geometry. The solid-state glass materials showed good optical power limiting at 532 nm for nanosecond pulses, which did not depend on the size or geometry of the AuNPs. In contrast to the observation at 532 nm, at 600 nm no optical limiting effect was observed. In these solids, as for dispersions of AuNPs, the optical limiting response is caused by scattering. [ABSTRACT FROM AUTHOR]

Gold nanoparticles have been the center of interest for scientists since many decades. Within the last 20 years, the research in that field has soared with the possibility to design and study nanoparticles with controlled shapes. From spheres to more complex shapes such as stars, or anisotropic architectures like rods or bipyramids, these new systems feature plasmonic properties making them the tools of choice for studies on light-matter interactions. In that context, fluorescence quenching and enhancement by gold nanostructures is a growing field of research. In this review, we report a non-exhaustive summary of the synthetic modes for various shapes and sizes of isotropic and anisotropic nanoparticles. We then focus on fluorescent studies of these gold nano-objects, either considering “bare” particles (without modifications) or hybrid particles (surface interaction with a chromophore). In the latter case, the well-known metal-enhanced fluorescence (MEF) is more particularly developed; the mechanisms of MEF are discussed in terms of the additional radiative and non-radiative decay rates caused by several parameters such as the vicinity of the chromophore to the metal or the size and shape of the nanostructures.