20 40 60 SO

GuKa. (degrees)

Uniformly dispersed transparent zinc ferrite nanoparticles were synthesized in a silica matrix with both the magnetic properties and optical transparency designed in the visible wavelength region [589]. The phases and morphologies of these zinc ferrite particles were examined. A much lower formation temperature of ZnFe2O4 in nanocomposites was observed, compared to conventional ceramic processing. The particle size of zinc ferrite varied with the initial drying temperature, suggesting that a well-established silica network provided more confinement to the growth of ZnFe2O4 particles. The optical properties of the nanocomposites were adjusted by varying the concentration of the zinc ferrite nanoparticles. The absorption edge at around 600 nm was blueshifted by 0.65 eV when the loading of ZnFe2O4 particles was decreased from 30 to 5 wt%, while the absorption coefficient remained below 400 cm-1 in the red visible region.

High-pressure optical absorption spectroscopic measurements of both erbium-doped and undoped Si nanoparticles were carried out in a diamond anvil cell up to pressures of 180 kbar [590]. The emphasis was with respect to the effect of particle size on the pressure dependence of the bandgap as well as the indirect examination of the structural impact of the erbium dopant on the pressure-induced phase transitions. In terms of electronic structure, these Er-doped Si nanocrystals acted very much like indirect gap silicon, with an observed bandgap pressure dependence of —1.4 x 10—6 eV/bar. Measurements of the optical spectra in terms of integrated area as a function of pressure of these doped nanoparticles revealed that the first-order phase transition must lie above 180 kbar, substantially elevated from the bulk value of 120 kbar.

Two procedures were presented which allowed the homogeneous incorporation of silica-coated gold nanoparticles within transparent silica gels [591]. There was no aggregation of the metal particles during sol-gel transition. The optical properties of the gels were compared with those of the starting sols and interpreted on the basis of the porous structure of the gets and standard optical theories.

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