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Oxide nanostructures and silica-based materials for optical technology

Norberto Chiodini, Alberto Paleari, Giorgio Spinolo, Anna Vedda

Our research is focused on the physical properties of silica-based glass and glass-ceramics for applications in photonics and microelectronics. Bulk and film materials are synthesized and investigated looking at the particular optical properties one can obtain and control by doping with active ions and crystalline nano-phase with non-linear and photosensitive features. Doped silica glass and glass-ceramics are technologically interesting for their signal amplification properties in the telecom windows, nonlinear optical properties induced by crystalline nano-phases, and good optical transmission and compatibility with existent glassy-silica based devices. Fundamental aspects of the study regard the physics of point defects in the amorphous silica network, the spectroscopy of rare earth ions and the study of excitation confinement effects in wide-energy-gap nanostructured materials. However, synthesis techniques have to be optimized to obtain, in amorphous silica, good dispersion of active ions and homogeneous dispersion of crystalline nano-clusters with specific non-linear optical properties and narrow size-distribution. Therefore our activity also regards the design and optimization of synthesis processes based on sol-gel methods. More specifically the main investigated items are: ● optical properties of rare earth ions such as Ce, Gd, Tb, Eu in silica, studying the interaction with the host matrix, to obtain materials suitable to be used as scintillators in the detection of low-energy ionizing radiations for industrial and medical applications. The role of point defects in crystalline scintillators is also investigated. ● optical properties of rare earth ions and defects in silica-based glassceramics with crystalline nano-phases (SnO2 or other matrices with low phonon energy), analyzing the interactions of active ions with the glass matrix and the nanocrystalline phase, looking at the optical properties useful in photonics. ● linear and non-linear optical properties of nanosized crystalline dispersions of SnO2 in silica, analyzing the possible applicability as photosensitive and cubic non-linear material. ● defect-related properties of thin SiO2 films for microelectronics, whose performances are severely limited by the presence of defects acting as charge traps. FACILITIES Synthesis laboratory: inorganic chemistry laboratory for sol-gel preparations in controlled conditions, comprising hoods and dry-boxes for the synthesis of bulk samples and films. Film deposition by spin-coating. Samples from aerogel can also be obtained by hypercritical drying process. Furnaces for densification processes in controlled temperature and atmosphere, as well as instrumentation for optical finishing. Physical characterization laboratory: optical absorption, photo- thermo- and radio-luminescence spectroscopy, micro-Raman scattering, refractive index and film thickness measurements, thermostimulated currents and complex impedance spectroscopy. Nd-YAG laser with second and fourth harmonic generation are also available to study photo-induced effects and nonlinearity.

Norberto Chiodini

Alberto Paleari

Giorgio Spinolo

Anna Vedda

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Measurement of thermoluminescence (TSL) di SiO2:Tb 0.04 %mol