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Barium titanate nanocrystallites were synthesized by a hydrothermal technique from barium chloride and tetrabutyl titanate. Single-crystalline cubic perovskite BaTiO3 consisting of spherical particles with diameters ranging from 10 to 30 nm was easily achieved by this route. In order to study the influence of the synthesis process on the morphology and the optical properties, barium titanate was also prepared by a solid-state reaction. In this case, only the tetragonal phase which crystallizes above 900°was observed. High-temperature X-ray diffraction measurements were performed to investigate the crystallization temperatures as well as the particle sizes via the Scherrer formula. The lattice vibrations were evidenced by infrared spectroscopy. Eu3+ was used as a structural probe, and the luminescence properties recorded from BaTiO3:Eu3+ and elaborated by a solid-state reaction and hydrothermal process were compared. The reddish emission of the europium is increased by the nanometric particles. [ABSTRACT FROM AUTHOR]

Tb3+-doped Y3Al5O12powders have been synthesized from alkoxide precursors using, or not using, acetylacetone as a chemical modifier. The terbium oxidation state and local environment of amorphous and crystallized powders have been comparatively investigated by means of X-ray absorption near-edge structures (XANES) and extended X-ray absorption fine structure (EXAFS) while laser-induced luminescence was used to study their optical properties. Excitation and emission spectra have been recorded and a relative luminescence yield has been assessed upon 277 nm excitation. Whatever the sample, the terbium oxidation state remains +III and, for a similar heating treatment until 900 °C, its local environment appears to be better organized in powders modified by acetylacetone. Structural parameters obtained during XAS study are consistent with the YAG structure in which Tb atoms are in solid solution with Y ones. Besides, Tb3+characteristic green luminescence has been recorded for all samples, even those amorphous. It has been evidenced that the use of acetylacetone leads to more efficient luminescent materials for calcination temperatures ranging from 400 °C to 900 °C upon 277 nm excitation. Discrepancies between optical properties will be discussed with regards to the terbium local environment and expected luminescence features. [ABSTRACT FROM AUTHOR]

We report here a facile, mild and low cost aqueous-based synthesis for the production of high quality CdZnS and Cu-doped CdZnS quantum dots (QDs). We demonstrate that the photoluminescence (PL) of the Cu-doped CdZnS nanocrystals could be tuned in the whole visible spectrum via the stoechiometric ratio of Cd/Zn precursors in the host CdZnS QDs and by tuning the particle size. By optimization of the experimental conditions (Cd/Zn ratio, reaction time, pH,…) and by varying the surface ligand, pure and highly emissive Cu:CdZnS QDs could be prepared. Moreover, by the growth of a ZnS shell around the Cu:CdZnS core, Cu:CdZnS/ZnS QDs with a PL quantum yield (PL QY) of 42% were constructed, which is the highest PL QY reported to date for Cu-doped CdZnS QDs prepared in aqueous solution. The optical properties and structure of the obtained dots were characterized by UV–visible spectroscopy, steady-state and time-resolved PL spectroscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Cu:CdZnS/ZnS QDs were subjected to various treatments such as long-term UV illumination, storage in biological buffers or pH changes, which are usually detrimental to QDs PL. No marked deterioration in PL properties during the previously described degradation processes was observed, thus indicating the high stability of the dots prepared. Due to their good water dispersibility and stability, the Cu:CdZnS/ZnS QDs developed herein can be a promising candidate for biolabelling applications. [ABSTRACT FROM AUTHOR]

A series of CuInZn x S 2+ x QDs has been successfully synthesized via a non-injection method by varying the amine (oleylamine, dioctylamine, dodecylamine, octadecylamine) during the ZnS shell introduction on the CuInS 2 core. The effects of these amines on the photoluminescence (PL) and on the morphology of CuInZn x S 2+ x QDs were explored. The optical features and structure of the obtained CuInZn x S 2+ x QDs have been characterized by UV–visible and fluorescence spectroscopies, time resolved PL, HR-TEM, XRD and EDX. After the ZnS shell introduction at 220 °C, CuInZn x S 2+ x QDs showed greatly improved properties, the PL quantum yield can reach up to 70% using dioctylamine. The formation of CuInZn x S 2+ x QDs results in a blue shift of both the absorption and PL due to the formation of the alloyed interfacial layer at CuInS 2 /ZnS during the shell growth. By increasing the reaction temperature to 250 °C (thermolysis of CuInZn x S 2+ x QDs), marked red-shifts in PL emissions accompanied by morphological changes of the nanocrystals were observed. The use of oleylamine generates 6.6 nm-sized pyramidally-shaped nanocrystals with a PL quantum yield of 22%. [ABSTRACT FROM AUTHOR]

The structural, morphological and optical properties of pure and Ca-doped zinc sulfide (ZnS:Ca) nanoparticles (NPs) prepared by hydrothermal method at different percentages of Ca are reported herein. The resulting NPs were characterized by X-ray diffraction analysis (XRD), Raman scattering, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. The XRD patterns confirmed the crystalline nature of all pure and doped NPs showing a single phase cubic blende structure, whereas the SEM micrographs showed sphere-shaped NPs. The sizes of the as-prepared NPs estimated by TEM were found to be in the range 44–147 nm. The PL emission spectra of ZnS:Ca nanocrystals excited at 400 nm consist of a broad band (420 nm–640 nm) characterized by two main contributions peaking at 484 and 533 nm. The overall maximum emission intensity is found for ZnS:3% Ca with internal quantum yield of 8.4%. • Ca2+ doped ZnS NPs were synthesis by a facile hydrothermal method. • PL excitation spectra show a characteristic band centered at 400 nm. • PL emission spectra show a large emission band covering the whole visible region. • Two main bands are observed for the non-doped sample due to intrinsic defects. • Ca2+ doped materials show greater quantum yields than undoped material. [ABSTRACT FROM AUTHOR]

The luminescence of Fluorescein, an inexpensive dye, ought to be interesting for lighting application devices such as commercial LEDs. However, the molecule suffers from severe instability, making it inappropriate for such applications. As previously studied, fluorescein molecules may be hosted in a layered double hydroxide (LDH), and the role of such an inorganic material in stabilizing the dye has been underlined. However, a deep understanding of the resulting optical properties is still required. Using extremely small amounts of fluorescein, it is demonstrated here that Zn 2 Al cation-based LDH tethering acts as a «solid solvent » for the dye, enabling its luminescence even in powder form, whereas fluorescein molecules on their own emit no luminescence at all in the solid state. However, aggregations of the dye occur in the interlamellar space, leading to non-radiative emission. Emission and excitation spectra, as well as fluorescence decays, are studied to explain the difference between the hybrid LDH-Fluorescein material and an aqueous solution of fluorescein. Additionally, LDH platelets are found to help the dispersion of the intercalated fluorescein in silicone to obtain a homogeneous composite film, which exhibits luminescent properties. Finally, an accelerated photoaging study demonstrates that the LDH-fluorescein filler has a pro-degradant effect on polymer aging under UV radiation. • Fluorescein is suitable to be intercalated in a Layered Double Hydroxide (LDH) matrix. • LDH provides a solvation effect as a solid powder for the fluorescein. • Hybrid LDH-Fluorescein material exhibits luminescence properties. • LDH-Fluorescein enables the dispersion of the dye in a polymer to achieve a homogeneous composite film. • LDH-Fluorescein filler has a pro-degradant effect on the composite film. [ABSTRACT FROM AUTHOR]

Abstract: CaTiO3:Pr3+ is a phosphor of great interest for electroluminescence application owing to its intense red emission characterized by CIE coordinates very close to those of the NSTC “ideal red”. In this paper, thin films of CaTiO3:Pr3+ are deposited by radiofrequency sputtering technique in pure argon and post-treated by Rapid Thermal Annealing (RTA). The influence of the deposition pressure (0.125–4.5Pa) and annealing conditions on the optical and electrical properties of the thin films is investigated. The chemical composition of the as-deposited films, checked by Rutherford Backscattering Spectroscopy (RBS), is close to that of the ceramic target used for the deposition. The crystal structure is confirmed to be orthorhombic by X-ray diffraction. We highlight an improvement of the optical and electrical properties of the films after RTA treatment. Moreover, a net gain is obtained by comparison with conventional thermal treatment procedures in classical furnaces, especially for the reduction of electrical defect densities. [Copyright &y& Elsevier]