Optical study of planar waveguides based on oxidized porous silicon impregnated with laser dyes

International audienceOxidized porous silicon optical planar waveguides were elaborated and impregnated with rhodamine B and rhodamine 6G. The waveguiding, absorption, and photoluminescence properties of these impregnated waveguides were studied. Successful impregnation of the structure with laser dyes is shown from photoluminescence and reflectivity measurements. Furthermore, the reflectivity spectra prove the homogenous incorporation of both dye molecules inside the pores of the matrices. The refractive indices of waveguide layers were determined before and after dye impregnation to indicate the conservation of guiding conditions. The optical losses in the visible wavelengths are studied as a function of dye concentration. The dye absorption is the main reason for these losses

Dielectric relaxation and polaronic hopping in Mn-substituted LaSrNiO4 nickelates prepared by mechanical milling method

The structures, microstructures and dielectric properties of LaSrNi1-xMnxO4 (x=0, 0.1, 0.2, 0.3 and 0.5) ceramics synthetized by mechanical milling followed by heat treatment were studied. One single tetragonal phase was revealed in all compounds. Structural parameters were obtained by Rietveld refinement. The substitution of Ni ions by Mn produces a variation of the lattice parameters but no phase change is observed. The surface morphology and elemental analysis of these samples were respectively investigated by Scanning Electron Microscopy (SEM) and energy dispersive X-ray technique (EDS). Giant dielectric response was observed in these ceramics, and at least two relaxations were found on the curve of the temperature dependence of dielectric constant. An equivalent circuit [R-C][R-CPE] was used to fit the experimental data and provide the activation energy of the thermally activated relaxation. The activation energy values confirm the thermally activated small polaronic hopping contribution to the giant dielectric response

Improve the dielectric properties of PrSrNi0.8Mn0.2O4 compounds by longer mechanical milling

Structural and dielectric properties of PrSrNi 0.8 Mn 0.2 O 4 ceramics elaborated by a rapid method combining mechanical milling and heat treatment were studied for the first time. The raw materials are milled at different times (t mil =0, 5, 10, 20 and 30 hours) and annealed at 1300°C for 8 hours to produce a revealed PrSrNi 0.8 Mn 0.2 O 4 single phase, exhibiting tetragonal structure with space group I4/mmm. This result was confirmed by using the TEM/ED pattern for sample milled at 30 h using the [001] orientation. The corresponding lattice images show a well-ordered compound, indicating the absence of stacking faults and the growth of the crystallites. Giant dielectric response was observed in these ceramics, and only one dielectric relaxation was found on the curve of a dielectric constant as a function of the temperature. The dielectric loss drops with increasing milling time. For 30 h milling it is divided by 100 at room temperature for low frequencies compared with 5 h milling. An equivalent circuit [R-C][R-CPE] was used to fit the experimental data and provide the activation energy of the thermally activated relaxation. Using the same nominal composition, the milling time has a major effect on the dielectric constant by significantly reducing the losses