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By systematically studying the evolution of the optical properties with the content of some doping elements (Eu and Tb) in cubic gadolinium oxide, we demonstrated that the luminescence quenching could be almost entirely suppressed by elaboration of the samples in the nanometer range. Indeed, even if the proportion of quenchers (here surface hydroxyl groups) does increase at this scale, each rare-earth cation possesses an electronic configuration that depends on its distance from the surface and then slightly differs from that of the surrounding atoms. This difference almost eliminates any resonant transfer of excitation between all the atoms within the particle and suppresses a significant proportion of non-radiative losses. As a consequence, the quantum yield is not affected by the phenomenon of luminescence quenching because of concentration that is usually encountered in macroscopic samples. The emission can then be increased by a factor of about 3 for Tb and 5 for Eu simply by increasing the doping content. Moreover, the lifetime is significantly increased compared to macroscopic samples and, contrary to what happens at the macroscopic scale, does not depend on the doping content. This result opens new strategies to increase the emission of many fluorophores already commercialized, provided that the bcc structure is effectively preserved in the desired application. [ABSTRACT FROM AUTHOR]

The organic/inorganic La 1-x LnxH(O3PCH3)2 (Ln = Eu, Tb) hybrids have been synthesized by hydrothermal synthesis. The crystal structure of LaH(O3PCH3)2 consists of chains of edge-sharing LaO8 polyhedra linked through PO3C tetrahedra. Photoluminescence of Eu 3+ , Tb 3+ and Eu 3+ /Tb 3+ co-doped materials have been investigated. The Eu and Tb hybrids show no concentration quenching versus doping rate suggesting energy migration through a percolation model. The Eu hybrids exhibit a red emission while the Tb ones exhibit, with the Tb rate increasing, a blue to green emission under a 378 nm excitation wavelength and a cyan to green emission under a 262 nm excitation wavelength. The doping rate dependent red shift results from a cross relaxation phenomenon between closed Tb 3+ ions. The blue to cyan shift observed for the slightly doped materials, when excitation wavelength shifts from 378 nm to 262 nm, is due to different relaxation phenomena, from the 5D3 level for a 378 nm excitation wavelength and from the 5D4 level via the 4f5d level for a 262 nm excitation wavelength. Under a 378 nm wavelength, the codoped La 0.93 Eu 0. 03 Tb 0.04H(O3PCH3)2 hybrid exhibits a white/cyan emission with CIE coordinates equal to x = 0.29, y = 0.37. [ABSTRACT FROM AUTHOR]

Nanostructured Tb(3+)-doped Gd(2)O(3) particles have been synthesized from chloride precursors by NaOH addition in a polyol medium. In-situ luminescent spectra have been investigated in order to follow up the process of formation and growth of these particles by varying parameters as the elaboration temperature and the rate of NaOH addition. Contrarily to all the literature related to the "polyol" synthesis, the paper proves that oxide particles can be directly formed at room temperature. These particles are also slightly bigger and organized in nanorods when NaOH is added progressively. Finally, it was found that the influence of further annealing up to 160 degrees C strongly depends on the NaOH addition rate. While preserving the oxide phase, annealing leads to bigger particles only in the case of a progressive addition of NaOH.