Long-lifetime fluorescence and crystal field calculation in Cr 4+-doped Li2MSiO4, M = Mg, Zn

The diffuse reflectance spectra of Cr:Li2MSiO4, M = Mg, Zn, indicate that in these compounds, chromium ions occur in the 4+, 5+, and 6+ oxidation states simultaneously. Under selective excitation in a Cr 4+ absorption band, a very long fluorescence decay time is observed for both compounds: ∼110 μs at room temperature and ∼300 μs at 30 K. These are by far the longest fluorescence lifetimes reported for Cr 4+ activated materials. In Cr4+:Li2MSiO 4, the 1E excited state level lies below the lowest component of the 3T2 level and the fluorescence decay time is dominated by the long-lifetime 1E level for which the transition to the ground state is spin-forbidden. The reverse situation occurs for the other Cr4+ doped compounds and their fluorescence lifetimes, governed by the short-lifetime 3T2 state, are only a few microseconds. A crystal field calculation, performed for Cr4+:Li 2MSiO4, confirms the above interpretation and supports the localization of Cr4+ at the silicon site in this compound. © 2003 Elsevier B.V. All rights reserved

Catalyst preparation for CMOS-compatible silicon nanowire synthesis

Metallic contamination was key to the discovery of semiconductor nanowires, but today it stands in the way of their adoption by the semiconductor industry. This is because many of the metallic catalysts required for nanowire growth are not compatible with standard CMOS (complementary metal oxide semiconductor) fabrication processes. Nanowire synthesis with those metals which are CMOS compatible, such as aluminium and copper, necessitate temperatures higher than 450 C, which is the maximum temperature allowed in CMOS processing. Here, we demonstrate that the synthesis temperature of silicon nanowires using copper based catalysts is limited by catalyst preparation. We show that the appropriate catalyst can be produced by chemical means at temperatures as low as 400 C. This is achieved by oxidizing the catalyst precursor, contradicting the accepted wisdom that oxygen prevents metal-catalyzed nanowire growth. By simultaneously solving material compatibility and temperature issues, this catalyst synthesis could represent an important step towards real-world applications of semiconductor nanowires.Comment: Supplementary video can be downloaded on Nature Nanotechnology websit

Long-lifetime fluorescence and crystal field calculation in Cr 4+-doped Li2MSiO4, M = Mg, Zn

The diffuse reflectance spectra of Cr:Li2MSiO4, M = Mg, Zn, indicate that in these compounds, chromium ions occur in the 4+, 5+, and 6+ oxidation states simultaneously. Under selective excitation in a Cr 4+ absorption band, a very long fluorescence decay time is observed for both compounds: ∼110 μs at room temperature and ∼300 μs at 30 K. These are by far the longest fluorescence lifetimes reported for Cr 4+ activated materials. In Cr4+:Li2MSiO 4, the 1E excited state level lies below the lowest component of the 3T2 level and the fluorescence decay time is dominated by the long-lifetime 1E level for which the transition to the ground state is spin-forbidden. The reverse situation occurs for the other Cr4+ doped compounds and their fluorescence lifetimes, governed by the short-lifetime 3T2 state, are only a few microseconds. A crystal field calculation, performed for Cr4+:Li 2MSiO4, confirms the above interpretation and supports the localization of Cr4+ at the silicon site in this compound. © 2003 Elsevier B.V. All rights reserved

Long-lifetime fluorescence and crystal field calculation in Cr 4+-doped Li2MSiO4, M = Mg, Zn

The diffuse reflectance spectra of Cr:Li2MSiO4, M = Mg, Zn, indicate that in these compounds, chromium ions occur in the 4+, 5+, and 6+ oxidation states simultaneously. Under selective excitation in a Cr 4+ absorption band, a very long fluorescence decay time is observed for both compounds: ∼110 μs at room temperature and ∼300 μs at 30 K. These are by far the longest fluorescence lifetimes reported for Cr 4+ activated materials. In Cr4+:Li2MSiO 4, the 1E excited state level lies below the lowest component of the 3T2 level and the fluorescence decay time is dominated by the long-lifetime 1E level for which the transition to the ground state is spin-forbidden. The reverse situation occurs for the other Cr4+ doped compounds and their fluorescence lifetimes, governed by the short-lifetime 3T2 state, are only a few microseconds. A crystal field calculation, performed for Cr4+:Li 2MSiO4, confirms the above interpretation and supports the localization of Cr4+ at the silicon site in this compound. © 2003 Elsevier B.V. All rights reserved

Hybrid organic-inorganic copolymers based on oxo-hydroxo organotin nanobuilding blocks

International audienc

A general route to alkylene-, arylene-, or benzylene-bridged ditin hexachlorides and hexaalkynides

The preparation of alkylene-, arylene-, or benzylene-bridged ditin hexachlorides in high yields from the reaction of the corresponding hexacyclohexylated compounds with tin tetrachloride is described. The tetragonal geometry of the tin atom of 1,4-bis(trichlorostannyl)-butane in the solid state indicates that no intramolecular or intermolecular interaction involving either end of the molecule exists in this compound. The ditin hexachlorides were successfully transformed in the corresponding hexaalkynides, precursors of hybrid materials

Un nouvel hydrure organostannique greffé sur support insoluble

International audienc