L.H.C. Andrade

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.

Spectroscopic properties, concentration quenching, and laser investigations of Yb 3+ -doped calcium aluminosilicate glasses

“Calcium aluminosilicate” (CAS) and “low silica calcium aluminosilicate” (LSCAS) OH− free glasses have demonstrated a good potential for solid-state laser media and luminophore hosts due to good thermal, optical, and mechanical properties. Some examples have already been shown with Nd3+, Er3+, Ce3+, and Ti3+ luminescent ions. In this work, Yb3+ rare-earth laser ions have been introduced into the two series of CAS and LSCAS glasses melted at 1600 °C in a vacuum furnace and have been optically characterized and compared. Special attention has been devoted to both structural characterization in relationship with spectroscopic properties and concentration quenching phenomenon in relationship with laser parameters. Laser measurements at 1037 nm have been successfully performed under laser diode pumping.

Determination of the biodiesel content in diesel/biodiesel blends: a method based on fluorescence spectroscopy.

Blends of biodiesel and diesel are being used increasingly worldwide because of environmental, economic, and social considerations. Several countries use biodiesel blends with different blending limits. Therefore, it is necessary to develop or improve methods to quantify the biodiesel level in a diesel/biodiesel blend, to ensure compliance with legislation. The optical technique based on the absorption of light in the mid-infrared has been successful for this application. However, this method presents some challenges that must be overcome. In this paper, we propose a novel method, based on fluorescence spectroscopy, to determine the biodiesel content in the diesel/biodiesel blend, which allows in loco measurements by using portable systems. The results showed that this method is both practical and more sensitive than the standard optical method.

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 ...

Long fluorescence lifetime of Ti3+-doped low silica calcium aluminosilicate glass.

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.

Optical multi-sites of Nd3+-doped CaMoO4 induced by Nb5+ charge compensator

Site-selective laser excitation and luminescence measurements at 15 K of CaMoO4 single crystal doped with Nd3+ and co-doped with Nb5+ charge compensator have been investigated in the spectral region of laser interest involving the transition. A larger than expected number of Nd3+ sites was found and a model to explain this result is presented. A partial diagram of 4F3/2 and 4I11/2 levels was constructed from the acquired data and their features are discussed.

Tunable color temperature of Ce 3+ /Eu 2+, 3+ co-doped low silica aluminosilicate glasses for white lighting

In this paper we report results of tunable lighting in Ce(3+)/Eu(2+,3+) doped low silica calcium aluminosilicate glass. Optical spectroscopy experiments indicate that there is a red color compensation from Eu(2+) and Eu(3+) to the green emission from Ce(3+), resulting in a broad and tunable emission spectra depending on the excitation wavelength. This result analysed in the CIE 1976 color diagram shows a close distance from the Plank emission and a correlated color temperature, varying from 5200 to 3500K. This indicates that our system can be easily excited by GaN based blue LEDs, being an interesting phosphor for white lighting devices.

Age-related changes in the surface pheromones of the wasp Mischocyttarus consimilis (Hymenoptera: Vespidae).

One of the most important attributes that allowed the evolution and maintenance of sociality in insects is their ability to distinguish members of their own colonies. The capacity for individual recognition in social insects is mediated by chemical signals that are acquired soon after the adult emerges, and vary according to the tasks performed by individuals in their colonies. We determined the time when adults of the wasp Mischocyttarus consimilis acquire the chemical signature of their colonies, as well as the variation in the cuticular hydrocarbon profiles of the exoskeleton of individuals, according to their functions in the colony. The method used was Fourier transform infrared photoacoustic spectroscopy directly on the gaster of each individual. Young wasps take three to four days to acquire the colonys chemical signature, with a small change on the fifth day, when the cuticular hydrocarbon profile of the workers is more similar to that of the queens than that of the males, probably because they are of the same sex, but primarily because of the similarity of tasks executed by these two groups of females in the colonies.

Effects of residue and antioxidant on thermo-optical properties of biodiesel

Thermal lens (TL) spectrometry was applied to soybean biodiesel samples, in order to assess the behavior of their thermo-optical properties during the preparation before and after the washing process. The study was based on the thermal diffusivity parameter, which is highly sensitive and is related to the chemical composition of the sample. The results showed a difference of approximately 20% between the initial (unwashed) and the final (washed) steps of biodiesel production. This behavior indicates that the residue of the biodiesel production influences the thermal diffusivity value. Consequently, TL spectrometry can be a useful methodology for certifying the quality of biodiesel during production.

Modeling the population lens effect in thermal lens spectrometry

We report a theoretical model and experimental results for laser-induced lensing in solids. The model distinguishes and quantifies the contributions from population and thermal effects. Laser-induced lensing in ytterbium-doped fluorozirconate glass ZBLAN:Yb(3+) is measured, and the thermal and optical properties obtained from analyzing the data with the proposed model agree well with published values. Photothermal techniques are used extensively for the investigation of laser and laser-cooling materials, and the model developed here enables the interpretation of convoluted laser-induced lensing signals that have contributions from different sources.