Delocalized Surface Electronic States on Polar Facets of Semiconductor Nanocrystals.

Wurtzite CdSe@CdS dot@platelet nanocrystals with (001) and (00-1) polar facets as the basal planes and (100) family of nonpolar facets as the side planes are applied for studying surface defects on semiconductor nanocrystals. When they are terminated with cadmium ions coordinated with carboxylate ligands, a single set of absorption features and band-edge photoluminescence (PL) with near unity PL quantum yield and monoexponential PL decay dynamics (lifetime ∼28 ns) are observed. In addition to these spectral signatures, when the surface is converted to sulfur-terminated, a second set of sharp absorption features with decent extinction coefficients and a secondary band-edge PL with low PL quantum yield and long-lifetime (>78 ns) PL decay dynamics are reproducibly recorded. Photochemical analysis confirms that the secondary UV-vis and PL spectral features are quantitatively correlated with each other. Chemical analysis and X-ray photoelectron spectroscopy measurements confirm that such secondary spectral features are well correlated with the sulfide (such as -SH) and disulfide (such as -S-S-) surface sites of a basal plane, which likely form surface hole electronic states delocalized on the entire basal plane. Results suggest that, for studying surface defects on semiconductor nanocrystals, it is essential to prepare a nearly monodisperse surface structure in terms of facets and surface chemical bonding.

Tunable fluorescence lifetime of Eu-PMMA films with plasmonic nanostructures for multiplexing.

A method to tune fluorescence lifetime of Eu-PMMA films is proposed, which consists of self-assembled gold nanorods on glass substrate covered by Eu-PMMA shell. The fluorescence lifetime is tunable in a wide range, and depends on aspect ratio and mutual distance of gold nanorods. In a single red color emission channel, more than six distinct fluorescence lifetime populations ranging from 356 to 513 µs are obtained. Through theoretical calculation, we attribute tunable fluorescence lifetime to the change of radiative and nonradiative decay rate and density of photon states. In addition, we use these as-prepared Eu-PMMA films for security data storage to demonstrate optical multiplexing applications. The optical multiplexing experiments show an interesting pseudo-information "8" and conceal the real messages "2" and "6".

Wide-Range Tunable Fluorescence Lifetime and Ultrabright Luminescence of Eu-Grafted Plasmonic Core-Shell Nanoparticles for Multiplexing.

Wide-range, well-separated, and tunable lifetime nanocomposites with ultrabright fluorescence are highly desirable for applications in optical multiplexing such as multiplexed biological detection, data storage, and security printing. Here, a synthesis of tunable fluorescence lifetime nanocomposites is reported featuring europium chelate grafted onto the surface of plasmonic core-shell nanoparticles, and systematically investigated their optical performance. In a single red color emission channel, more than 12 distinct fluorescence lifetime populations with high fluorescence efficiency (up to 73%) are reported. The fluorescence lifetime of Eu-grafted core-shell nanoparticles exhibits a wider tunable range, possesses larger lifetime interval and is more sensitive to separation distance than that of ordinary Eu-doping core-shell type. These superior performances are attributed to the unique nanostructure of Eu-grafed type. In addition, these as-prepared nanocomposites are used for security printing to demonstrate optical multiplexing applications. The optical multiplexing experiments show an interesting pseudo-information "a rabbit in a well" and conceal the real message "NKU."

Optical properties of silver nanoprisms and their influences on fluorescence of europium complex.

The optical properties of truncated triangular silver nanoprisms and their influences on the fluorescence of europium complex Eu(TTFA)(3) were investigated in theory and experiment separately. In theory, we found that the fluorescence of Eu ions would be greatly enhanced by these nanoprisms, the enhancement factor of the fluorescence depended on the concentrations of nanoprisms. They were verified in the experiment. The influence of silver nanoprisms on the radiative and nonradiative decay rates of Eu ions were also deduced, and found that the silver nanoprisms greatly reduced the energy loss caused by the nonradiative decay.

The role of metal film electron density in a surface plasmon polariton assisted light emitter.

A novel and simple Sm(3+)-doped-polymer/Ag/ SiO(2) trilayer structure was fabricated to investigate the impact of surface plasmon polaritons (SPPs) on the emission quantum efficiency of the dipole emitter Sm(3+). Photoluminescence (PL) enhancement factors for samples with different Ag thicknesses (30-70 nm) were found to be different when the thickness of the Sm(3+)-doped-polymer film was kept constant (220 nm). Theoretical analysis suggests that the electron density of the metal film plays an important role in the SPP assisted PL enhancement process, and this was confirmed in a Sm(3+)-doped-polymer/Ag/Au/ SiO(2) multilayer structure.