Suitable labels are at the core of Luminescence and fluorescence imaging and sensing. One of the most exciting, yet also controversial, advances in label technology is the emerging development of quantum dots (QDs)--inorganic nanocrystals with unique optical and chemical properties but complicated surface chemistry--as in vitro and in vivo fluorophores. Here we compare and evaluate the differences in physicochemical properties of common fluorescent labels, focusing on traditional organic dyes and QDs. Our aim is to provide a better understanding of the advantages and limitations of both classes of chromophores, to facilitate label choice and to address future challenges in the rational design and manipulation of QD labels.

Graphene quantum dots (GQDs) are nanometer‐sized fragments of graphene that show unique properties, which makes them interesting candidates for a whole range of new applications. This review article gives an overview of the synthesis, properties and applications of GQDs. Synthesis methods discussed include top‐down and bottom‐up approaches. Properties such as luminescence up‐ and down‐conversion have been used in applications ranging from energy conversion to bio‐analytics. This article provides an overview of the state‐of‐the‐art and highlights promising findings as well as potential future directions of the research field.

In this Letter we report the plasmon-enhanced upconversion in single NaYF(4) nanocrystals codoped with Yb(3+)/Er(3+). Single nanocrystals and gold nanospheres are investigated and assembled in a combined confocal and atomic force microscope setup. The nanocrystals show strong upconversion emission in the green and red under excitation with a continuous wave laser in the near-infrared at 973 nm. By the use of the atomic force microscope, we couple single nanocrystals with gold spheres (30 and 60 nm in diameter) to obtain enhanced upconversion emission. An overall enhancement factor of 3.8 is reached. A comparison of time-resolved measurements on the bare nanocrystal and the coupled nanocrystal-gold sphere systems unveil that faster excitation as well as faster emission occurs in the nanocrystals.

A new method for the preparation of single quantum dots (QDs) in silica spheres has been developed. The work involves an oil-in-water microemulsion system with cyclohexane as the “oil” phase and Synperonic NP-5 as the surfactant. Reaction parameters such as reactant concentrations, time, and temperature were studied. The method resulted in smooth silica nanoparticles of good monodispersity and high luminescence with single QDs in the center. Elucidating the coating mechanism was attempted. Possible mechanisms include a phase transfer by ligand exchange and a surfactant-supported mechanism. In contrast to sol−gel based methods, this is a straightforward, simple “one-pot” synthesis for such particles. The resulting nanoparticles could be used for further silica growth and assembly of photonic structures, for biolabeling, or for other applications.

We report a simple method for the fast synthesis of highly photoluminescent InP and InP/ZnS core-shell nanocrystals (NCs) covering a wide range of emissions from blue to the near infrared. Both InP and InP/ZnS NCs were prepared in one-step, in a one-pot reaction within 20 min using an InCl 3 complex as a precursor and zinc carboxylate as an initiator and stabilizer. The quantum yields of the InP and InP/ZnS NCs were 30% and 60%, respectively. This new synthetic method allows fast and reproducible preparation of InP and InP/ZnS NCs with a quality comparable to that of the frequently used CdSe-based ones. It is anticipated that these particles can be used to replace CdSe for many applications.