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A water-based route has been demonstrated for synthesizing ZnSe and Cd-doped ZnSe (ZnxCd1-xSe, 0 < x< 1) quantum dots (QDs) that have tunable and narrow photoluminescence (PL) peaks from the ultraviolet A (UVA) to the blue range (350−490 nm) with full-width at half-maximum (fwhm) values of 24−36 nm. Hydrazine (N2H4) was used to maintain oxygen-free conditions, allowing the reaction vessel to be open to air. The properties of the QDs were controlled using the thiol ligands, 3-mercaptopropionic acid (MPA), thiolglycolic acid (TGA), and l-glutathione (GSH). On the basis of optical spectra, linear three-carbon MPA attenuated nucleation and growth, yielding small ZnSe QDs with a high density of surface defects. In contrast, TGA and GSH produced larger ZnSe QDs with lower surface defect densities. The absorption spectra show that growth was more uniform and better controlled with linear two-carbon TGA than branched bifunctional GSH. After 20 min of growth TGA-capped ZnSe had an average diameter of 2.5 nm based on high-resolution transmission electron microscopy images; these nanocrystals had an absorbance peak maximum of approximately 340 nm (3.65 eV) and a band gap PL emission peak at 372 nm (3.34 eV). Highly fluorescent ZnxCd1-xSe QDs were fabricated by adding a Cd−thiol complex directly to ZnSe QD solutions; PL peaks were tuned in the blue range (400−490 nm) by changing the Zn to Cd ratio. The Cd-bearing nanocrystals contained proportionally more Se based on X-ray photoelectron spectroscopy, and Cd−Se bonds had ionic character, in contrast to primarily covalent Zn−Se bonds. [ABSTRACT FROM AUTHOR]

Nearly monodispersed self-assembled tin dioxide (SnO 2) nanospheres with intense photoluminescence (PL) were synthesized using a new wet chemistry technique. Instead of coprecipitating stannous salts, bulk tin (Sn) metal was oxidized at room temperature in a solution of hydrogen peroxide and deionized water containing polyvinylpyrrolidone (PVP) and ethylenediamine (EDA). SnO 2nanocrystals were produced with diameters of ∼3.8 nm that spontaneously self-assembled into uniform SnO 2nanospheres with diameters of ∼30 nm. Analysis was performed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV−vis absorption spectroscopy, PL spectroscopy, and fluorescence lifetime measurements. The SnO 2nanospheres displayed room-temperature purple luminescence with an intense band at 394 nm (∼3.15 eV) and a high quantum yield of ∼15%, likely as a result of emission from the surface states of SnO 2/PVP complexes. The present study could open a new avenue to large-scale synthesis of self-assembled functional oxide nanostructures with technological applications as purple emitters, biological labels, gas sensors, lithium batteries, and dye-sensitized solar cells. [ABSTRACT FROM AUTHOR]