V. C. S. Reynoso

CdTe quantum dots by melt heat treatment in borosilicate glasses

CdTe quantu m dots in borosilicate glasses were produced and their growth kinetics, the effects of quantum confinement for electrons and phonons and the time resolved optical transmission were studied. Quantum dots in the range of 10 to 25 with a 5% size dispersion were grown. The growth kinetics were studied by small angle X-ray scattering using synchrotron light. A spherical k .p model for the electron confinement explains absorption data and selection rules, and a dielectric continuum model for the phonon confinement could explain the resonant longitudinal and surface optical phonons, as well as their overtone combinations. The time response of absorption was studied by a pump-probe measurement on the femtosecond time scale. For samples showing a large amount of surface traps the recovery time can be as fast as 300 fs, while for an almost surface trap free sample it remains on the 1-3 ps time scale.

Preparation and characterization of heavy-metal oxide glasses: Bi2O3–PbO–B2O3–GeO2 system

High-refractive-index glasses of heavy-metal oxides have large optical non-linearities which make them promising for optoelectronic applications. This paper describes the fabrication and characterization of the xBi2O3–PbO–B2O3–(52–x)GeO2(BPBG) glass system with x= 10, 15, 20, 30 and 35. The BPBG glasses were melted in a high-purity alumina crucible placed in a Super Khantal resistance furnace at 1000 °C for 30 min and then poured onto a steel plate. The characterization was done by X-ray diffraction (XRD), density, dilatometry, light absorption (UV–VIS–IR) and linear refractive-index measurements. The infrared spectra show the presence of BiO6 and GeO6 in the glass structure suggesting a network former role for the bismuth oxide. These measurements allowed us to estimate the non-linear refractive index n2, using Lines formula, to be as high as 1.5 × 10–18 m2 W–1.

Preparation and characterization of TiO2-BaO-ZnO-B2O3 glass systems for optical devices

We study the TiO2-BaO-ZnO-B2O3 glass system, where the ZnO and B2O3 compositions were constant and the ratio TiO2/BaO was varied from 0.87 to 1.76. A super kanthal resistance furnace was used to melt the compounds inside an alumina crucible, at 1200 °C, for 10 min. After melting, the glasses were poured out into steel moulds and rapidly cooled by quenching. The glasses obtained were homogeneous, bubble free and transparent. They were characterized by X-ray diffractometry, Fourier transform infrared spectroscopy (FTIR), UV-VIS spectroscopy, dilatometry, density and linear refractive index. An infrared “cut off” caused by the composition influence was found in both IR and UV-vis spectra. From dilatometry Td and Tg were verified as being anomalous. The linear thermal expansion coefficient α presented an anomalous behaviour in relation to TiO2 concentrations. The density and linear refractive index increased with increasing TiO2/BaO ratio arriving at their peak value of TiO2/BaO=1.5 and then decreasing. The dependence of softening point Td on the ratio TiO2/BaO exhibited the same behaviour. It is suggested that Ti4+ plays a dual part in the glass system, assuming a predominantly tetrahedral coordination in the low titania region and a predominantly octahedral coordination in the high titania region. With a heat treatment of the glass around 600 °C, we observed a rapid change of refractive index with increasing temperature.

Estudo das propriedades ópticas em vidros 0,3La2S3-0,7Ga2S 3

In this work we describe the synthesis and characterization of chalcogenide glass (0.3La2S3-0.7Ga2S 3) with low phonons frequencies. Several properties were measured like Sellmeier parameters, linear refractive index dispersion and material dispersion. Samples with the composition above were doped with Dy2S3. The absorption and emission characteristics were measured by electronic spectroscopy and fluorescence spectrum respectively. Raman and infrared spectroscopy shows that these glasses present low phonons frequencies and strucuture composed by GaS4 tetrahedrals. The Lines model was used for calculate the coefficients values of the non linear refractive index.