Rapid progress in tailoring the size and shape of semiconductor nanocrystals (quantum dots) enables a high degree of control over their optical and electronic properties. This control can be harnessed for applications in biological assays, optoelectronic integration, and wireless-systems engineering. In optoelectronics, size tunability of quantum dots permits control over the spectrum of absorption for photovoltaic and photoluminescent, stimulated emission, and electroluminescence applications, [1±4] whereas in biological applications, this allows spectral multiplexing and coding. [5] In both applications, luminescence in the near-infrared region is urgently needed: in optoelectronics to bridge interconnects with shortand medium-haul networks, and in biological applications to exploit the spectral windows in water and biological absorption. An ideal nanocrystal (NC) synthetic route combines features that have so far been demonstrated in isolation. Synthesis in aqueous solution, or transfer from organic media to water, is highly desirable for compatibility with biological assays.[5] It also enables multilayer polymer±nanocrystal device fabrication for heterostructure engineering through the use of alternating aqueous/organic solvents in sequential layers.Other crucial features of synthetic route are simplicity, use of non-toxic solvents, and moderate reaction temperatures. [6,7] From the point of view of the resulting material properties, the NCs desired in the above-mentioned applications would be size-tunable in the near-IR spectral range; have a high quantum yield, and exhibit stable, narrow fluorescence peaks [8] requiring no yield-reducing size-selective precipitation.To date, no route to synthesis of quantum dots (QDs) has been reported that accommodates all of these features simultaneously. We report herein a one-stage water-based synthesis of stable and monodisperse PbS NCs that show photo-and electroluminescence in the spectral range 1000±1400 nm. It is the combination of the simplicity of water-based synthesis, a one-stage process with no need in encapsulation or size-selective precipitation, relatively low toxicity, [9,10] stability, size tunability, and excellent performance that make these NCs promising in optoelectronic and biological applications. PbS nanocrystals were prepared in aqueous solutions using a mixture of thiols as a stabilizing agent. We admit that waterbased synthesis and thiol ligands have been used in II±VI nanoparticle synthesis. [11,12] This approach, however, has not been tested in the preparation of PbS NCs: previous reports on PbS nanoparticles synthesis in aqueous solutions employed poly(vinyl alcohol), poly(vinyl pyrrolidone), gelatin, and DNA as stabilizers. [13,14] These reports and our experiments indicate that these methods result in agglomerates of poly/ nanocrystals of very small diameter (~1 nm) and absorption and luminescence in the visible spectral range. We examined a number of different capping agents, such as thiobutanol, thiohexanol, triglycolic acid, thioglycero...

Na+ was incorporated into red‐emitting CaMoO4:Eu3+ phosphor to form solid solutions and reduce the crystal symmetry. For a fixed Eu3+ concentration, the luminescent properties as a function of Na+ concentrations were systematically studied under near‐ultraviolet (UV) excitation. Enhanced red emission at 613 nm was observed and the strongest intensity was 4.5 times that of the sample without Na+. Differing from the charge‐compensation mechanism, this enhancement was related to the structural distortion and decreasing centrosymmetry. The increased ratios of red emission (5D0 → 7F2) to orange (5D0 → 7F1) in intensity revealed that the structural adjustment was achieved in the phosphors via the incorporation of Na+.