A. Steimacher

A step forward toward smart white lighting: Combination of glass phosphor and light emitting diodes

We present our recent achievements of a glass able to produce smart white light combining a glass phosphor with light emitting diodes (LEDs). The combined emissions of Ce3+-doped calcium aluminosilicate glass and the 405 nm LED using the Commission Internationale de l’Eclairage 1931 chromatic diagram showed that this system presents an emission close to the ideal white light and allows tunability. In addition, the glass blue emission overlaps with the spectral range of the retinal photoreceptors involved in circadian responses. This glass combined with UV LED emission is suitable for circadian lights and therefore may contribute to improve environmental lighting and human well being.

Thermal properties of natural nanostructured hydroxyapatite extracted from fish bone waste

In a previous study, natural hydroxyapatite (HAp) from the bones of Brazilian river fish was calcined at 900 °C (4–12 h), and optical characterization using the near infrared photoacoustic spectroscopy technique enabled the establishment of 8 h as the best calcination time for nanostructure stabilization when milled in a high-energy milling device [T. M. Coelho, E. S. Nogueira, W. R. Weinand, W. M. Lima, A. Steimacher, A. N. Medina, M. L. Baesso, and A. C. Bento, J. Appl. Phys. 100, 094312 (2006)]. The fish wastes used were from species such as pintado (Pseudoplatystoma corruscans), jau (Paulicea lutkeni), and cachara (Pseudoplatystoma fasciatum). In this study, the characterization of the thermal properties of the same natural HAp is discussed for samples milled from 0 to 32 h, with nanostructures from 80 to 24 nm. The powders were pressed into disks at 350 MPa and sintered for 4 h at 1000 °C. Thermophysical parameters were obtained by thermal wave interferometry and nonadiabatic relaxation calorimetry. ...

Characterization of natural nanostructured hydroxyapatite obtained from the bones of Brazilian river fish

In this study, the characterization of the optical properties of natural hydroxyapatite (HAp) [Ca10(PO4)6(OH)2] is discussed. In the first stage of the experiment, natural HAp was processed from the bones of Brazilian river fish such as pintado (Pseudoplatystoma corruscans), jau (Paulicea lutkeni), and cachara (Pseudoplatystoma fasciatum). The bones were calcined at 900°C for different amounts of time (4–12h) and reduced to powder using two different milling times (2 and 4h) in a high-energy ball mill, in order to determine the best procedure for obtaining natural nanostructured HAp powder for the study. In the second stage, material calcined for 8h was milled for 2, 4, 8, and 16h. The techniques of photoacoustic spectroscopy, scanning electron microscopy, and flame atomic absorption spectrometry were applied to characterize these samples. The O–H stretching shown by photoacoustic spectroscopy was correlated to the HAp nanostructure. Structural analysis indicated a Ca∕P ratio close to 1.67 (∼1.64±0.04) an...

Relations among nonbridging oxygen, optical properties, optical basicity, and color center formation in CaO–MgO aluminosilicate glasses

In this study the relations among nonbridging oxygen (NBO), optical properties, optical basicity, and color center formation in CaO–MgO aluminosilicate glasses were studied. Samples containing (in mol %) 35.9–57.5 of CaO, 16–27.7 of Al2O3, 7.9–41.6 of SiO2, and 6.5–6.9 of MgO were measured by optical absorption and excitation, luminescence, and Raman spectroscopy. The results showed that when the SiO2 content was increased, the absorption edge shifted toward lower wavelengths and the bonds between O2− ions and cations became more covalent. These observations were confirmed by Raman results that showed a decrease in the number of NBO per silicon tetrahedron as a function of SiO2 content. The results indicate that the effects of higher NBO concentration are the narrowing of the band gap energy and the delocalization of O2− electrons, which facilitates the O2− electrons to be trapped by anion vacancies and, consequently, forming color centers. The relationship between color center formation and SiO2 content ...

Thermal characterization in vitro of human nail: photoacoustic study of the aging process.

In the present work, the rear photoacoustic signal technique is used to determine thermal properties of human nails. The aging process of the human nail is analyzed through its thermal diffusivity and specific heat and using these results, thermal conductivity and thermal effusivity is determined. The study in vitro of this natural polymer showed a minimum for thermal properties to age about 20 years and an increase and possible saturation of them for ages over 50 years. The minimum value found for thermal diffusivity was close to 10 × 10−4 cm2 s−1 with saturation near 18 × 10−4 cm2 s−1. Thermal conductivity and effusivity presents the same behavior.

Inversion in the temperature coefficient of the optical path length close to the glass transition temperature in tellurite glasses

In this study, thermal lens spectrometry was applied to determine the thermo-optical properties of fragile tellurite glasses as a function of temperature, close to the glass transition region. The results showed an inversion from positive to negative values in the temperature coefficient of the optical path length occurring after the glass transition temperature, which is the region where structural changes from the TeO4 trigonal bipyramidal unit to a TeO3 trigonal pyramid containing nonbridging oxygen take place. In addition, the thermal diffusivity values as a function of temperature exhibited behaviors that were related to thermodynamic and kinetic structural changes in the glass.

Thermal lens and interferometric method for glass transition and thermo physical properties measurements in Nd 2 O 3 doped sodium zincborate glass

In this work the time resolved thermal lens method is combined with interferometric technique, the thermal relaxation calorimetry, photoluminescence and lifetime measurements to determine the thermo physical properties of Nd(2)O(3) doped sodium zincborate glass as a function of temperature up to the glass transition region. Thermal diffusivity, thermal conductivity, fluorescence quantum efficiency, linear thermal expansion coefficient and thermal coefficient of electronic polarizability were determined. In conclusion, the results showed the ability of thermal lens and interferometric methods to perform measurements very close to the phase transition region. These techniques provide absolute values for the measured physical quantities and are advantageous when low scan rates are required.

Temperature and wavelength dependence of the thermo-optical properties of tellurite and chalcogenide glasses

The refractive index and the temperature coefficient of the optical path length change of tellurite 80TeO2:20Li2O and chalcogenide glasses 72.5Ga2S3:27.5La2O3 were determined as a function of temperature up to 150 °C and wavelength in the range between 454 and 632.8 nm. The tellurite glass exhibits the usual refractive index dispersion in the wavelength range analyzed, while anomalous refractive index dispersion was observed for the chalcogenide glass between 454 and 530 nm. The dispersion parameters were determined by means of the single-effective oscillator model. In addition, a strong dependence of the temperature coefficient of the optical path length on the photon energy and temperature was found for the chalcogenide glass. The latter was correlated to the shift of the optical band gap or electronic edge with temperature, which was interpreted by the electron-phonon interaction model.

Angular dependence of the thermal-lens effect on LiSrAlF 6 and LiSrGaF 6 single crystals

We apply thermal-lens (TL) spectrometry to measure the angular dependence of the TL effect on colquiriite single crystals. The experiments were performed with LiSrAlF(6) and LiSrGaF(6) using a two-beam mode-mismatched configuration. The results show that it is possible to minimize the TL effect by selecting the appropriate crystal orientation. Our data also show that the anisotropy of the linear thermal expansion coefficient drives the amplitude of the TL effect, including the inversion from focusing to defocusing as the crystal orientation angle tends to the c-axis direction. The results may be useful for those working to develop a high-power laser using LiSrAlF(6)(:Cr) and LiSrGaF(6)(:Cr) single crystals, allowing for optimization of the designed laser cavity.

Temperature dependence of the thermo-optical properties in fragile tellurite glasses

In this work the thermal lens spectrometry (TLS) in function of the temperature was applied in TeO/sub 2/-Li/sub 2/O (TL) and TeO/sub 2/-Li/sub 2/O-TiO/sub 2/ (TLT) tellurite glasses in order to determine their thermo-optical properties. By fitting the thermal lens transient signal the parameter /spl theta/ can be obtained, which is proportional to (-P/sub abs/ds/dT) and is related to the thermal lens signal amplitude, where P/sub abs/ is the absorbed power. The ds/dT signal inversion related in this work is the first experimental observation of this phenomenon.