Copper nanoparticles received much attention due to its high electrical conductivity, high melting point, low electrochemical migration behavior and low cost. Top down (physical methods) and bottom up (chemical and biological) approaches adopted for the synthesis of copper nanoparticles are reported. The property of copper nanoparticles mainly depends on the synthesis route and their process parameters. The influence of process parameters on the morphology, growth and yield of the nanoparticles by adopting various synthesis methods are discussed in detail. From the earlier reports, it is proved that electrochemical and chemical reduction method have received much higher attention due to their simple operation, low cost, faster reaction rate, high yield, environment friendly and low energy consumption. The characterization techniques, advantages and limitations of each synthesis methods are also discussed. The extensive applications of copper nanoparticles in various fields are also highlighted.

We propose a model for quantum dot light emitting devices (QD-LEDs), which explores the most important parameters that control their electrical characteristics. The device is divided into a hole transport layer, several quantum dot layers, and an electron transport layer. Conduction and recombination in the central quantum dot region is described by a system of coupled rate equations, and the drift-diffusion approximation is used for the hole and electron transport layers. For NiO/Si-QDs/ZnO devices with suitable design parameter, the current and light output are primarily controlled by the quantum dot layers, specifically, their radiative and non-radiative recombination coefficients. Radiative recombination limits the device current only at sufficiently large bias. V C 2013 AIP Publishing LLC. [http://dx.

A highly water-dispersible NaYF4:Ce/Tb (core), NaYF4:Ce/Tb@NaYF4(core/shell) and NaYF4:Ce/Tb@NaYF4@SiO2 (core/shell/SiO2) nanoparticles (NPs) were synthesized via a general synthesis approach. The growth of an inert NaYF4 and silica shell (~14 nm) around the core-NPs resulted in an increase of the average size of the nanopaticles as well as broadening of their size distribution. The optical band-gap energy slightly decreases after shell formation due to the increase the crystalline size. To optimize the influence of shell formation a comparative analysis of photoluminescence properties (excitation, emission, and luminescence decay time) of the core, core/shell, and core/shell/SiO2 NPs were measured. The emission intensity was significantly enhanced after inert shell formation around the surface of the core NPs. The Commission International de l'Eclairage chromaticity coordinates of the emission spectrum of core, core/shell, core/shell/SiO2 NPs lie closest to the standard green color emission at 545 nm. By quantitative spectroscopic measurements of surface-modified core-NPs, it was suggested that encapsulation with inert and silica layers was found to be effective in retaining both luminescence intensity and dispersibility in aqueous environment. Considering the high aqueous dispersion and enhanced luminescence efficiency of the core-NPs make them an ideal luminescent material for luminescence bioimaging and optical biosensors.

The design of nanostructured materials with highly stable water-dispersion and luminescence efficiency is an important concern in nanotechnology and nanomedicine. In this paper, we described the synthesis and distinct surface modification on the morphological structure and optical (optical absorption, band gap energy, excitation, emission, decay time, etc.) properties of highly crystalline water-dispersible CaF:Ce/Tb nanocrystals (core-nanocrystals). The epitaxial growth of inert CaF and silica shell, respectively, on their surface forming as CaF:Ce/Tb@CaF (core/shell) and CaF:Ce/Tb@CaF@SiO (core/shell/SiO) nanoarchitecture. X-ray diffraction and transmission electron microscope image shows that the nanocrystals were in irregular spherical phase, highly crystalline (~20 nm) with narrow size distribution. The core/shell nanocrystals confirm that the surface coating is responsible in the change of symmetrical nanostructure, which was determined from the band gap energy and luminescent properties. It was found that an inert inorganic shell formation effectively enhances the luminescence efficiency and silica shell makes the nanocrystals highly water-dispersible. In addition, Ce/Tb-co-doped CaF nanocrystals show efficient energy transfer from Ce to Tb ion and strong green luminescence of Tb ion at 541 nm(D→F). Luminescence decay curves of core and core/shell nanocrystals were fitted using mono and biexponential equations, and R regression coefficient criteria were used to discriminate the goodness of the fitted model. The lifetime values for the core/shell nanocrystals are higher than core-nanocrystals. Considering the high stable water-dispersion and intensive luminescence emission in the visible region, these luminescent core/shell nanocrystals could be potential candidates for luminescent bio-imaging, optical bio-probe, displays, staining, and multianalyte optical sensing. A newly designed CaF:Ce/Tb nanoparticles via metal complex decomposition rout shows high dispersibility in aqueous solvents with enhanced photoluminescence. The epitaxial growth of inert CaF shell and further amorphous silica, respectively, enhanced their optical and luminescence properties, which is highly usable for luminescent biolabeling, and optical bioprobe etc.

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Bismuth nanoparticles (NPs) have been prepared by the pulsed laser ablation technique using the third harmonics of a Nd-YAG laser. UV-absorption and TEM micrographs show Bi NPs of spherical shape with the average particle size ranging from 15 to 20 nm. These NPs were dispersed with Tb(3+) ions and their complex with salicylic acid (Sal) in polyvinyl alcohol to obtain thin films. The influence of Bi NPs on the emissive properties of Tb(3+) ions and the [Tb(Sal)3(phen)] complex has been studied by luminescence spectroscopy using 266 nm and 355 nm as excitation wavelengths. The luminescence intensity of Tb(3+) ions complexed with Sal in the thin polymer films increased significantly as compared to the Tb(3+) ions in the presence of Bi NPs on excitation at 355 nm. However, terbium ions in the case of the [Tb(Sal)3(phen)] complex together with NPs show an intense and extended emission spectrum in the 375-700 nm range for transitions arising from (5)D3 and (5)D4 levels to different (7)F(J) levels on 266 nm excitation. The luminescence enhancement has also been supported by lifetime measurements.

White light-emitting devices based on the combined emission from red CdSe/ZnS quantum dots, green phosphorescent, and blue fluorescent organic molecules Inorganic quantum dots (QDs) have excellent optoelectronic properties. But, due in part to a lack of a suitable medium for dispersion, they have not been extensively used in optoelectronic devices. With the advent of organic semiconductors, the integration of quantum dots into optoelectronic devices has become possible. Such devices are termed as hybrid organic/inorganic quantum dot light emitting devices. In hybrid organic/inorganic quantum dot light emitting devices, the mechanisms of charge and/or energy transfer into the quantum dots include Forster energy transfer and direct charge injection. Forster energy transfer involves formation of excitons on organic semiconductors, followed by an energy transfer onto the inorganic quantum dots, where the exciton recombines resulting in emission of a photon. Direct charge injection is the mechanism in which the electrons and holes are directly injected into the quantum dots and they recombine on the quantum dots to result in a photon. Which mechanism is operating in a device has been a subject of contention. In this work, by using various device configurations, we show that both these mechanisms can operate independently to maximize the quantum dot light emission in such devices.