Nanocrystalline SnO 2 particles have been synthesized by a simple sol-gel method. The structural and optical properties of these SnO 2 particles are investigated using X-ray powder diffraction, transmission electron microscopy, UV-visible absorption, and photoluminescence spectroscopy. The oxygen-vacancies-related photoluminescence of pure, cerium-, and manganese-doped SnO 2 nanoparticles was systematically investigated. The origin of the luminescence is assigned to the recombination of electrons in a conduction band with holes in the V o •• center. Experimental results reveal that increasing calcining temperature can decrease the oxygenvacancies-related luminescence intensity of the sample. After introducing Ce 3+ /Mn 2+ ions into the host, the oxygen-vacancies-related luminescence has been enhanced remarkably resulting from the formation of many more oxygen vacancies. The dependence of the oxygen-vacancies-related luminescence intensity on the Ce 3+ / Mn 2+ concentration is also discussed.

A freely tunable polarization rotator for broadband terahertz waves is demonstrated using a three-rotating-layer metallic grating structure, which can conveniently rotate the polarization of a linearly polarized terahertz wave to any desired direction with nearly perfect conversion efficiency. This low-cost, high-efficiency, and freely tunable device has potential applications as material analysis, wireless communication, and THz imaging.

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Carbon dots (C dots) with biocompatibility, brightness, stability against photoirradiation and salt, and ease in preparation have become important materials for sensing and imaging. They can be prepared from natural materials and small organic molecules through hydrothermal, microwave‐assistant, and electrochemical methods, with advantages of simplicity and low cost. To enhance the quantum yields of C dots in the red and near‐infrared regions, doping of C dots with heteroatoms such as nitrogen and sulfur has been suggested. C dots both with and without being functionalized recognition elements such as antibodies and aptamers are selective and sensitive for sensing of analytes, including metal ions (e.g., Fe3+, Hg2+, Cu2+), small molecules (e.g., H2O2, cysteine, glutathione), and biopolymers like proteins, as well as for in vitro and in vivo imaging. Depending on the size, charge, and surface ligands of C dots used to label cells, fluorescence images of different organelles are shown. Multicolor images of bacteria, mammalian cells, and plant tissues incubated with C dots are realized when excited at different wavelengths. In this review, many excellent sensing and imaging examples of C dots are presented to highlight their features and to show their challenges for analytical applications.