J. H. Rohling

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.

High fluorescence quantum efficiency of 1.8 μm emission in Tm-doped low silica calcium aluminate glass determined by thermal lens spectrometry

In this work, thermal lens spectrometry is performed to determine the fluorescence quantum efficiency (η) of the 3F4 level (1.8 μm emission) of 4 and 5 wt % Tm-doped water free low silica calcium aluminate glass. The η value obtained for both high Tm contents was approximately 30%, which is in agreement with the Judd–Ofelt calculation. It is also verified that heat generation under 0.79 μm pumping, which presents a high quantum defect, is minimized by a cross-relaxation mechanism. The high η values, and the excellent chemical and thermomechanical properties indicate this system is a potential host material for diode-pumped laser sources operating in the midinfrared spectral range.

The Effect of Relative Humidity on Binary Gas Diffusion

The dependence of diffusion coefficient of O2-N2 mixture in the presence of water vapor was experimentally determined as a function of relative humidity (RH) with different temperatures using an in-house made Loschmidt diffusion cell. The experimental results showed that O2-N2 diffusion coefficient increased more than 17% when RH increased from 0% to 80% at 79 degrees C. In the experiments, the RH in both top and bottom chambers of the diffusion cell were the same, and the pressure inside the diffusion cell was kept as ambient pressure (1 atm.). Maxwell-Stefan theory was employed to analyze the mass transport in the diffusion cell, and found that there was no effective water vapor diffusion taking place, indicating that the gas diffusion in this ternary (O2-N2-water vapor) system could be considered binary gas (O2-N2) diffusion. The Fuller, Schettler, and Giddings (FSG) empirical equation of the kinetic theory of gases was generalized to accommodate the dependence of the binary diffusion coefficient on the RH. The prediction of the generalized equation was found to be consistent with experimental results with the difference of less than 1.5%, showing that the generalized equation could be applied to calculate the diffusion coefficients of the binary gaseous mixture with different temperature and RH values. The effect of water vapor on the increase of O2-N2 diffusion coefficient was discussed using molecule theory.

Study on the observation of Eu2+ and Eu3+ valence states in low silica calcium aluminosilicate glasses

The optical, magnetic and structural properties of Eu doped low silica calcium aluminosilicate glasses were investigated. The optical absorption coefficient presented two bands at 39,246 and 29,416 cm(-1), which were assigned respectively to the [Formula in text], and [Formula in text] transitions of Eu(2+). The fluorescence measured at 300 K on a sample doped with 0.5 wt% of Eu(2)O(3) exhibited a broad band centered at 17,350 cm(-1), which is attributed to the [Formula in text] transition of Eu(2+), whereas the additional peaks are due to the [Formula in text] transitions of Eu(3+). From magnetization and XANES data it was possible to evaluate the fractions of Eu(2+) and Eu(3+) for the sample doped with 0.5 and 5.0 wt% of Eu(2)O(3), the values of which were approximately 30 and 70%, respectively.

Thermal lens temperature scanning for quantitative measurements in complex fluids

In this work thermal lens spectrometry is applied to investigate the thermo-optical properties of complex fluids as a function of the temperature. The method is applied in poly(vinyl chloride), in polycarbonate and in lyotropic liquid crystals as the testing samples. The focus of the discussion will be in the temperature range where the phase transitions occur. The perspective of future studies in this area will be discussed.

Laser-induced chemical reaction characterization in photosensitive aqueous solutions.

A dual-wavelength on/off-excitation thermal lens technique was used to identify and quantify a laser-induced chemical reaction in ionic aqueous solutions of Fe(II)-TPTZ. On/off modeling was used to fit the TL experimental data, which provided the primary effect generated during laser-excitation. The addition of HCl in the solutions reduced the activation barrier; this behavior followed the Arrhenius correlation. The nature of the photo-oxidation of Fe(II)-TPTZ complex is discussed. The results suggest that this technique may contribute to the understanding of the dynamics of complex reactions, which may lead to a more precise determination of the physicochemical properties involved in a photochemical reaction.

Time-resolved thermal lens determination of the thermo-optical coefficients in Nd-doped yttrium aluminum garnet as a function of temperature

In this work, time-resolved thermal lens measurements are carried out in Nd-doped yttrium aluminum garnet laser crystal as a function of temperature. The temperature coefficient of the optical path length, the thermal diffusivity, and the thermal conductivity were determined in the temperature range between 22°C and 180°C. In addition, the specific heat was measured by the thermal relaxation method in the same temperature range. The results showed that the thermal conductivity and the temperature coefficient of the optical path length are responsible for the strong increase of the thermal lens amplitude when the sample temperature was increased. These results suggest that the time resolved procedure is useful in the study of laser materials and may be an important tool for laser designers.

Produção de Filmes Didáticos de Curta Metragem e CD-ROMs para o Ensino de Física

This article intend to show the program of the Laboratory of Visual Creation of the Department of Physics of the State University of Maringa in the production and popularization of short-duration educational lms of physics.

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.

Thermal lens temperature scanning for quantitative measurements in transparent materials (invited)

In this work the ability of thermal lens spectrometry for different temperature studies in transparent materials is discussed. The method was applied in polymers and optical glasses to measure the thermo-optical properties as a function of the temperature. The focus of the discussion will be on the temperature range where the glass transition occurs. The perspectives of future studies in this area will be discussed.