In this study the relations among nonbridging oxygen ͑NBO͒, 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 Al 2 O 3 , 7.9-41.6 of SiO 2 , and 6.5-6.9 of MgO were measured by optical absorption and excitation, luminescence, and Raman spectroscopy. The results showed that when the SiO 2 content was increased, the absorption edge shifted toward lower wavelengths and the bonds between O 2− 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 SiO 2 content. The results indicate that the effects of higher NBO concentration are the narrowing of the band gap energy and the delocalization of O 2− electrons, which facilitates the O 2− electrons to be trapped by anion vacancies and, consequently, forming color centers. The relationship between color center formation and SiO 2 content was confirmed by optical spectroscopic measurements under UV radiation.
This Letter reports the formation of Ti3+ in OH- free aluminosilicate glass melted under vacuum condition, with a very long lifetime (170 micros) and broad emission band shifted towards the visible region. This lifetime value was attributed to the trapping of the excited electrons by the glass defects and detrapping by thermal energy, and it is 2 orders of magnitude higher than those published for Ti3+ doped materials. Our results suggest that this glass is a promising system to overcome the challenge of extending the spectral range of traditional tunable solid state lasers towards the visible region.
In this work we present the spectroscopic assignments of Ti 3+ and Ti 4+ in titanium-doped OH − free lowsilica calcium aluminosilicate glass and the influence of structural defects on the observed long lifetime and high fluorescence intensity of Ti 3+ ions. Measurements were performed with electron-spin resonance ͑ESR͒, time resolved luminescence, ultraviolet-visible ͑UV-VIS͒ optical excitation and emission spectra, and conventional optical absorption and photoconductivity. The ESR data showed that the Ti 3+ / Ti 4+ ratio increases with the doping concentration and that the Ti 3+ ions are in distorted octahedral sites. The assignment of the Ti 3+ and Ti 4+ emission bands derived from the spectroscopic results allowed us to propose a model explaining the mechanisms involved in the luminescence processes. The long lifetime of the Ti 3+ emission around 650 nm ͑on the order of 170 s͒ is about two orders of magnitude higher than the values found in the literature and was associated to the trapping of the excited electrons by the glass defects followed by detrapping via defect recombination. In conclusion, the combination of several techniques permitted a comprehensive characterization of the Ti ions in this OH − free glass.
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’Éclairage 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 diffusion and thermoelastic bending are two consequences of heating generated on the sample surface. Both are employed in Open Photoacoustic Cell (OPC) technique to measure the thermal diffusivity of the sample. In this work, we explore the potential use of the OPC technique to study the effectiveness of thermoelastic bending process and thermal diffusion process on photoacoustic signal (S) generation in solids. More specifically, it is observed that if the thermoelastic bending process becomes more effective while the sample thickness is decreased, this information can be used to obtain a method to self-check the value of the thermal diffusivity parameter measured. The method is based on the measurement of the thermoelastic bending parameter as a function of the sample thickness (ls). The expected dependence of the thermoelastic bending parameter (C2) with the sample thickness, according to the theoretical model, is C2 ∝ ls−3. Our results for aluminum metallic samples give a C2 ∝ ls−2.8 dependence. Also, a thermal diffusivity value of αexp = (8.4 ± 0.3) × 10−5 m2/s was measured for metallic aluminum. This value is in good agreement when compared with the theoretical value αAl = 8.6 × 10−5 m2/s.
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