The mechanisms of exciton generation and recombination in semiconductor nanocrystals are crucial to the understanding of their photo-physics and for their application in nearly all fields. While many studies have been focused on type-I heterojunction nanocrystals, the photo-physics of type-II nanorods, where the hole is located in the core

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The authors took an independent and closer look at the family of red-emitting rhodamine dyes known for a decade due to their excellent performance in STED microscopy. After the family...

We report on the sol-gel fabrication, using a dip-coating technique, of low-loss Eu-doped 70SiO2 -[Formula: see text] HfO2-xZnO (x = 2, 5, 7 and 10 mol%) ternary glass-ceramic planar waveguides. Transmission electron microscopy and grazing incident x-ray diffraction experiments confirm the controlled growth of hybrid nanocrystals with an average size of 3 nm-25 nm, composed of ZnO encapsulated by a thin layer of nanocrystalline HfO2, with an increase of ZnO concentration from x = 2 mol% to 10 mol%  in the SiO2-HfO2 composite matrix. The effect of crystallization on the local environment of Eu ions, doped in the ZnO-HfO2 hybrid nanocrystal-embedded glass-ceramic matrix, is studied using photoluminescence spectra, wherein an intense mixed-valence state (divalent as well as trivalent) emission of Eu ions is observed. The existence of Eu(2+) and Eu(3+) in the SiO2-HfO2-ZnO ternary matrix is confirmed by x-ray photoelectron spectroscopy. Importantly, the Eu[Formula: see text]-doped ternary waveguides exhibit low propagation losses (0.3 ± 0.2 dB cm(-1) at 632.8 nm) and optical transparency in the visible region of the electromagnetic spectrum, which makes ZnO-HfO2 nanocrystal-embedded SiO2-HfO2-ZnO waveguides a viable candidate for the development of on-chip, active, integrated optical devices.

Graphene quantum dots (GQDs) are nanoparticles that consist of a nanometer-sized core of graphene with diverse chemical groups on its boundary. Due to their advantageous properties, they are considered to be a promising material for optoelectronics, bioimaging, or photovoltaics. Despite considerable efforts that have been focused on unraveling the mechanism of their photoluminescence, many fundamental details are still unclear. Here, we report on a single-particle multimodal study that provides new insight into the photoluminescence properties of emission centers of GQDs in various local chemical environments. In particular, we show that the properties that are associated with emission centers of GQDs are significantly more sensitive to the structure of the particle itself than to a nonuniform local chemical environment. A better understanding of the dependence of GQDs’ emission states on the complex local chemical environment is an important step toward finding new ways of controlling the optical properties of GQDs and of optimizing their use in various applications.