Monodisperse ZnO:Eu nanocrystals were prepared by the codecomposition of metal acetylacetonate precursors in a mixture of oleylamine and 1-octadecene. They have been systematically characterized by means of X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma atomic emission spectrometry, Raman spectroscopy, and photoluminescence spectroscopy. The as-obtained ZnO:Eu nanocrystals are mainly composed of nanopyramids and dot-shaped nanocrystals and have an average size in the range of 16−32 nm. The valence states of europium ions in the nanocrystals are determined as predominately +3. With increasing dopant concentration of Eu3+ ions, Eu2O3 species tend to segregate on the surfaces of nanocrystals. Under a typical band-edge excitation of ZnO (380 nm), a direct energy transfer from ZnO host to Eu3+ ions, together with a distinct quenching of broad defect emission of ZnO, was observed for the as-obtained doped nanocrystals.

Efficient Energy Transfer in Monodisperse Eu-Doped ZnO Nanocrystals Synthesized from Metal Acetylacetonates in High-Boiling Solvents

Size-correlated single-molecule fluorescence measurements on CdSe quantum dots functionalized with oligo(phenylene vinylene) (OPV) ligands exhibit modified fluorescence intermittency (blinking) statistics that are highly sensitive to the degree of ligand coverage on the quantum dot surface. As evidenced by a distinct surface height signature, fully covered CdSe−OPV nanostructures (∼25 ligands) show complete suppression of blinking in the solid state on an integration time scale of 1 s. Some access to dark states is observed on finer time scales (100 ms) with average persistence times significantly shorter than those from ZnS-capped CdSe quantum dots. This effect is interpreted as resulting from charge transport from photoexcited OPV into vacant trap sites on the quantum dot surface. These results suggest exciting new applications of composite quantum dot/organic systems in optoelectronic systems.

Coverage-mediated suppression of blinking in solid state quantum dot conjugated organic composite nanostructures.

Synthesis and photoluminescence of Eu-doped ZnO microrods prepared by hydrothermal method

Synthesis and luminescence properties of Eu3+-doped ZnO nanocrystals by a hydrothermal process

Here, we report the role of crystal structure and crystal size on the photoluminescence properties of Ce3+ ions in Y2SiO5 nanocrystals. The emission at 430 nm (5d1 → 4f1) and lifetime of the excite...

Luminescence of Ce3+ in Y2SiO5 nanocrystals: Role of crystal structure and crystal size.

When an atomic impurity is incorporated in a nanoparticle of size 2 to 10 nm, the quantum-confinement provided by the dielectric-boundary of the host-nanoparticle modulates the properties of the atom. This Quantum Confined Atom (QCA) shows extraordinary changes in its luminescent properties and is associated with the modulation of the excited states of the caged atom. These “atomically engineered nanomaterials,” pioneered and developed by Nanocrystals Technology, yield several novel properties and are expected to be a major contributor to the future of nanotechnology. Efficient QCA-Nanophosphors that emit different colors depending on the specific choice of the 'caged atom' are being developed for applications to solid-state lighting. We have made two key contributions to development of SSL. (1) By embedding nanoparticles in the encapsulant, the refractive index is enhanced to 1.8 that allows us to enhance Light Extraction Efficiency (LEE) of the LED chip. (2) Incorporation of appropriate nanophosphors enables efficient down-conversion with high color-quality. The combination of an optically transparent downconverter and high refractive index in an encapsulant has yielded Phosphor-Converted LEDs (PC-LEDs) that yield higher package optical efficiency at lower package-level cost. The LEE and wall plug efficiency enhancement due to the HRI encapsulant is applicable across the entire visible spectrum of monochromatic HB-LED lamps.

Quantum-confined-atom-based nanophosphors for solid state lighting

When an atomic impurity is incorporated in a nanoparticle of size 2 to 10 nm, the quantum-confinement provided by the dielectric-boundary of the host-nanoparticle modulates the properties of the atom. This Quantum Confined Atom (QCA) shows extraordinary changes in its luminescent properties and is associated with the modulation of the excited states of the caged atom. These atomically engineered nanomaterials, pioneered and developed by Nanocrystals Technology, yield several novel properties and are expected to be a major contributor to the future of nanotechnology. Efficient QCA-Nanophosphors that emit different colors depending on the specific choice of the 'caged atom' are being developed for applications to solid-state lighting. We have made two key contributions to development of SSL. (1) By embedding nanoparticles in the encapsulant, the refractive index is enhanced to 1.8 that allows us to enhance Light Extraction Efficiency (LEE) of the LED chip. (2) Incorporation of appropriate nanophosphors enables efficient down-conversion with high color-quality. The combination of an optically transparent downconverter and high refractive index in an encapsulant has yielded Phosphor-Converted LEDs (PC-LEDs) that yield higher package optical efficiency at lower package-level cost. The LEE and wall plug efficiency enhancement due to the HRI encapsulant is applicable across the entire visible spectrum of monochromatic HB-LED lamps.

Quantum Confined Atom based nanophosphors for solid state lighting

Recently there has been a great deal of attention focused on rare-earth doped nanocrystals (DNCs) as a new class of luminescent nanomaterials with novel and tunable optical properties. Such species have properties that make them attractive candidates for biological tags such as narrow spectral width and very high photochemical stability. However, the transitions that give rise to visible luminescence of rare-earth ions are nominally forbidden making luminescence from single ions very difficult to detect. In our experiments, single europium and terbium ions in isolated yttrium oxide nanocrystals (2–15 nm diam.) were probed using time-resolved fluorescence microscopy techniques. In contrast with luminescence from larger crystals containing several ions, small particles believed to contain single ions show fascinating on-off behavior on a variable time scale as well as multiple discrete luminescence intensity levels. The latter behavior suggests interesting application in optical data storage.

Probing single ion luminescence in rare-earth doped nanocrystals

Isolated europium-doped metal-oxide nanoparticles were probed by size-correlated high-numerical-aperture (far-field) imaging techniques. A modified Digital Instruments Bioscope atomic force microscope mounted upon a Nikon TE300 inverted microscope was used to interrogate (dry) particles ranging in size from 2 to 150 nm on the surface of a glass or quartz coverslip. These experiments revealed several interesting features of doped-nanoparticle luminescence such as Poissonian occupation statistics, size-dependent luminescence efficiency enhancement for particle sizes of <10 nm, and correlation of interesting transient behavior at particle sizes of <5 nm.

Size-correlated spectroscopy and imaging of rare-earth-doped nanocrystals

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Quantum-confined-atom-based nanophosphors for solid state lighting

Quantum Confined Atom based nanophosphors for solid state lighting

Probing single ion luminescence in rare-earth doped nanocrystals

Size-correlated spectroscopy and imaging of rare-earth-doped nanocrystals