We report the observation of visible-light emission at room temperature from high fluence (0.3–3×1017 cm−2) Si+ implanted thermal SiO2 layers grown on silicon substrates. Significant blue-light emission and an intense broad luminescent band with a peak beyond 750 nm are observed after annealing at high temperature (T≥1000 °C). The red-light emission, present only in the highest fluence implant, is attributed to the luminescence emitted from silicon nanocrystals produced by silicon precipitation. The presence of silicon nanocrystals is confirmed by transmission electron microscopy. Significant blue-light emission is visible after thermal annealing in the 1×1017 cm−2 fluence implant. The peak position shifts from 490 to 540 nm by increasing the annealing cycles temperature.

Thisis an author version of the contribution published on:Questa è la versione dell'autore dell'opera: By Federico Cesano, Serena Bertarione, Andrea Piovano, Giovanni Agostini, Mohammed Mastabur Rahman, Elena Groppo, Francesca Bonino, Domenica Scarano, Carlo Lamberti, Silvia Bordiga, Luciano Montanari, Lucia Bonoldi, Roberto Millini and XRPD, HRTEM, Raman and UV-Vis characterization methods have been applied to obtain information on the morphology and the structure of the catalysts (including degree of staking and structural disorder) as well as on the vibrational and spectroscopic properties. It is shown that, when compared with HRTEM results, XRPD, Raman and UV-Vis data give a realistic information on the staking degree, on the particle size distribution and on the heterogeneity of supported MoS 2 particles on the various supports. EXAFS and XANES spectroscopies have been also used to set up the best sulfidation procedure on the MoS 2 /SiO 2 system, and the obtained recipe has been adopted for the MoS 2 /γ-Al 2 O 3 and MoS 2 /MgO systems. UV-vis analysis under controlled atmosphere has been performed to understand the effect of reductive and sulfiding treatments on the presence of sulfur vacancies and on the valence state of Mo ions associated with them. To explore the structure of coordinatively unsaturated Mo sites after reducing or sulfiding treatments (with CS 2 or, occasionally, with H 2 S), in situ FTIR of CO adsorbed at low-temperature has been performed on all samples. It is demonstrated that CO is a sensitive probe for coordinatively unsaturated sites and that the formation of sulfur vacancies on the MoS 2 surface upon reduction in pure H 2 at 673 K is accompanied by an increase of the coordinative unsaturation and a decrease of the valence state of a fraction of surface Mo cations, mainly located on corner and edge sites. Considering the non planarity of a consistent fraction of lammelae (as revealed in particular by HRTEM of MoS 2 on Al 2 O 3 and MgO), the presence of reducible Mo ions, located in defective positions on basal planes, cannot be excluded. Furthermore, it is demonstrated that this process can be reversed upon interaction with the sulfiding agent and that this reversible behavior is really mimicking some of the elementary acts occurring in the HDS process. Comparing the results obtained by all the adopted characterization techniques, it is concluded that the reductive effect of H 2 preferentially affects the particles characterized by the lowest staking degree. The complexity of the IR results suggests that the adopted reduction procedure in pure H 2 at 673 K induces the formation of several type of sulfur vacancies, presumably located in different crystallographic positions of the MoS 2 particles. In conclusion, the IR results obtained with the CO probe fully support the idea that the adopted reduction procedure in pure H 2 at 673 K is not only inducing the formation of several families of sulfur vacancies but that a continuity exists between the stages associated with the reducti...

ECS-14, a crystalline microporous hybrid organic-inorganic aluminosilicate, has been synthesized by using 1,4-bis-(triethoxysilyl)-benzene (BTEB) as a source of silica. Its structure contains a system of linear channels with 12-membered ring openings, running along the [001] direction, resembling the pore architecture of the AFI framework type.

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Organic–inorganic aluminosilicate hybrids are an attractive new class of materials that add organic functionalities to conventional properties of solid inorganic catalysts. ECS-17, a novel crystalline hybrid, was synthesized using 1,4-bis-(triethoxysilyl)-benzene as the sole silicon source. Its structure was solved by direct methods starting from high-resolution synchrotron X-ray diffraction data and is composed of inorganic layers, characterized by 10 rings, held together by phenylene rings. ECS-17 is the first aluminosilicate built from only the three-ring secondary building unit. This new material shows intriguing reversible collapsibility upon dehydration/rehydration. Mild thermal treatment under vacuum causes its crystalline structure to collapse due to facile elimination of the water molecules around the cations. Successive exposure to ambient atmospheric moisture gives back the hydrated crystalline form. ECS-17 shows remarkably high thermal stability for a hybrid, being stable up to 450 °C under vacuum and breaking down at 350 °C in air. Structural, thermal, and optical properties were examined by X-ray powder diffraction, thermogravimetric analysis, nuclear magnetic resonance, and ultraviolet–visible-near-infrared reflectance and fluorescence spectroscopies