ENHANCEMENT IN UV SENSING PROPERTIES OF Zno:Ag NANOSTRUCTURED FILMS BY SURFACE FUNCTIONALIZATION WITH NOBLE METALIC AND BIMETALLIC NANOPARTICLES

In this study, Ag-doped ZnO (ZnO:Ag) nanostructured films were functionalized with silver nanoparticles (Ag NPs), silver-platinum bimetallic nanoparticles (AgPt NPs) and silver-gold bimetallic NPs (AgAu NPs) using a gas phase PVD process based on a Haberland type gas aggregation cluster source and unipolar DC planar magnetron sputtering. Ultraviolet (UV) sensing investigations showed arespectable time constants reduction for rising and decaying photocurrents, as well as an increase for the UV response. Compared to a pristine nanostructured film the surface functionalization with Ag, AgPt and AgAu increased the UV response by factors of 2.7, 3.5 and 4, respectively. The increased performances of the here presented ZnO:Ag nanostructured films functionalized with monometallic and bimetallic NPs based photodetectors are explained by the increased lifetime of photogenerated electron –hole pairs, as well as the formation of nanoscale Schottky barriers at the interface of Au/ZnO:Ag and Pt/ZnO:Ag

Experimental evidence of luminescence quenching at long coupling distances in europium (III) doped core-shell gold silica nanoparticles

International audienceLocalized surface plasmons can modify linear optical responses of materials located in their vicinity. In particular, rare earth ions luminescence can be enhanced by gold nanoparticles. Luminescence exaltation is a complex phenomenon that depends on multiple parameters, a critical one being the coupling distance between the emitting species and the plasmonic core. An original multilayer nanostructure designed to precisely control the distance between the gold cores and the luminescent ions, and to study its effect on the luminescent properties is presented here. Homogeneous silica shells with controlled thicknesses adjustable from 2 to 50 nm and rare earth ion doping rates up to 2x10(20) Eu/cm(3) of silica were deposited onto gold nanospheres. These original nanostructures are then incorporated into densified sol-gel silica composites with high-optical quality. Luminescence properties are studied for increasing gold-europium (III) distances. Strong luminescence quenching is evidenced for coupling distances up to 28 nm

Élaboration des cristaux LnCOB pour la conversion de fréquence en accord de phase non critique.

Nous avons étudié différentes substitutions dans le Ca4GdO(BO3)3 (GdCOB) par Sr2+, La3+, Bi3+, Y3+, Sc3+. L'objectif est de réaliser des dispositifs émettant dans le bleu ou le vert en associant un cristal laser à un cristal non linéaire, le GdCOB « modifié », en accord de phase non critique. Nous avons comparé quelques propriétés de doublage de fréquence à 930 nm (YAP: Nd3+) du Gd1-xYxCOB à celles du YCOB en accord de phase « critique » dans les plans YX (φ = 44,6°) et ZX (θ = 22,8°)

Optical spectroscopy and magnetic behaviour of Sm3+ and Eu3+ cations in Li6Eu1-xSmx(BO3)3 solid solution

A new borate solid solution series of powders, Li6Eu1-xSmx(BO3)3 (LSEBx, x = 0.35, 0.5, 0.6, 1), were synthesized by solid-state reaction, characterized and their luminescent properties were investigated. The absorption spectra indicate that absorption takes place mainly from the Sm3+6H5/2 ground state, with a strong band at 405 nm. The photoluminescence spectra reveal that the Eu3+ red emission intensity strongly depends on the Sm3+ content x. Judd-Ofelt theory was applied to experimental data for the quantitative determination of phenomenological parameters Ωi (i = 2, 4, 6) Judd Ofelt parameters, radiative transition rates and emission quantum efficiency. Owing to the energy transfer from Sm3+ to Eu3+ the intense red light detected at 613 nm at room temperature under UV or blue light excitation, was improved by ∼35% as compared with Sm3+-free samples. This energy transfer was confirmed by faster decay times of Sm3+ as energy donors. Moreover, the energy transfer between Sm3+ and Eu3+ is unidirectional and irreversible, implying that the energy transfer wastage between Sm3+ and Eu3+ is very low. Magnetic susceptibility (χ) measurements of LSEBx were carried out in the temperature range 2-320 K and are used to compare calculated and experimental energy levels

Judd-Ofelt analysis of luminescence emission from Li6Eu1−xSmx(BO3)3Li_6Eu_{1-x}Sm_x(BO_3)_3 single crystal

A detailed spectroscopic study of Eu3+ ions in the monoclinic Li6Eu1-xSmx(BO3)3 (LSEBx) crystals is reported. The symmetry of the local environment of Eu3+ activators has been confirmed within the framework of the standard Judd-Ofelt theory, using Ω2, Ω4 and Ω6 intensity parameters derived from emission spectra data analysis. With these intensity parameters various radiative properties, like spontaneous emission probability, branching ratio, stimulated emission cross-section and radiative lifetime, have been calculated. The maximum stimulated emission cross section corresponding to the 5D0 → 7F2 transition is 3×10-21 cm2 at 611 nm. Under UV excitation, the LSEBx crystals provide intense red photoluminescence intensity. These results revealed that LSEBx might be potential materials for optical applications

Solid-State and Solution Studies of {Ln n (SiW 11 O 39 )} Polyoxoanions: An Example of Building Block Condensation Dependent on the Nature of the Rare Earth

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Rare earth doped mesoporous hybrid thin films with tunable optical responses

International audienceOptical quality mesostructured silica thin films functionalized with three large hydrophobic organosilylated quinizarin derivatives are prepared via evaporation induced self-assembly (EISA). Incorporation of Eu3+ is performed by post-reacting the functionalized layers with several europium precursors. Unambiguous location of the quinizarin moieties inside the porosity and their accessibility to Eu3+ ions are demonstrated using XRD, SAXS and fluorescence measurements. Complexation of Eu3+ reduces the fluorescence of quinizarin; for some europium precursors an energy transfer between the grafted organic dye and the lanthanide is clearly observed. The luminescence intensity of Eu3+ can be tuned by varying the nature of the rare earth precursor, the mesophase and the chelate itself. The resulting optical responses differ with respect to concentration, lifetime and local environment of Eu3+ inside the thin films. Additionally, efficient energy transfer from Tb3+ to Eu3+ and electronic coupling probed by EPR between Cu2+ cations trapped in such mesoporous hybrid films give strong evidence of the presence of several metal ions per pore