M. L. Baesso

Curcumin–β-cyclodextrin inclusion complex: Stability, solubility, characterisation by FT-IR, FT-Raman, X-ray diffraction and photoacoustic spectroscopy, and food application

Curcumin was complexed with β-CD using co-precipitation, freeze-drying and solvent evaporation methods. Co-precipitation enabled complex formation, as indicated by the FT-IR and FT-Raman techniques via the shifts in the peaks that were assigned to the aromatic rings of curcumin. In addition, photoacoustic spectroscopy and X-ray diffraction, with the disappearance of the band related to aromatic rings, by Gaussian fitting, and modifications in the spectral lines, respectively, also suggested complex formation. The possible complexation had an efficiency of 74% and increased the solubility of the pure colourant 31-fold. Curcumin-β-CD complex exhibited a sunlight stability 18% higher than the pure colourant. This material was stable to pH variations and storage at -15 and 4°C. With an isothermal heating at 100 and 150°C for 2h, the material exhibited a colour retention of approximately 99%. The application of curcumin-β-CD complex in vanilla ice creams intensified the colour of the products and produced a great sensorial acceptance.

Optical band-gap determination of nanostructured WO3 film

The optical band-gap energy of a nanostructured tungsten trioxide film is determined using the photoacoustic spectroscopy method under continuous light excitation. The mechanism of the photoacoustic signal generation is discussed. The band-gap energy is also computed by other methods. The absorption coefficient as well as the band-gap energy of three different crystal structures of tungsten trioxide is calculated by a first-principles Green’s function approach using the projector augmented wave method. The theoretical study indicates that the cubic crystal structure shows good agreement with the experimental data.

Mode-mismatched thermal lens spectrometry for thermo-optical properties measurement in optical glasses: a review

Abstract In this work, the application of thermal lens spectrometry (TLS) to study thermo-optical and spectroscopic properties of optical glasses is described. The theoretical basis for quantitative measurements is discussed together with the advantages and limitations of the method as compared with conventional measurements. The technique is applied to determine the thermal diffusivities, temperature coefficient of optical path length changes, d s/ d T , and the fluorescence quantum efficiencies of several glasses such as fluorides, chalcogenides, chalcohalides, soda lime and low silica calcium aluminosilicate. For some of these glasses, the effect of glass composition on thermo-optical properties was studied. For aluminosilicate glasses was observed an 8% decrease of the thermal diffusivity with the increase of Nd2O3 doping. Five kinds of fluoride glasses were studied and it was observed that fluorindate and fluoaluminate present better thermo-optical properties compared to fluorozirconate glasses: thermal diffusivity ∼ 20% higher and d s/ d T ∼ 50% lower (in modulus). All fluoride glasses had negative d s/ d T and all the other glasses a positive d s/ d T . For fluoride glasses, the TLS measurements were performed up to the glass transition temperature ( T g ). Near T g thermal diffusivity decreases and d s/ d T increases, both by one order of magnitude. The TLS was used to determine fluorescence quantum efficiency and concentration quenching in Nd3+-doped glasses (aluminosilicate and fluorozirconate). These results were compared with the Judd–Ofelt calculations.

Antibacterial photodynamic therapy for dental caries: evaluation of the photosensitizers used and light source properties.

Photodynamic therapy studies have shown promising results for inactivation of microorganisms related to dental caries. A large number of studies have used a variety of protocols, but few studies have analyzed photosensitizers and light source properties to obtain the best PDT dose response for dental caries. This study aims to discuss the photosensitizers and light source properties employed in PDT studies of dental caries. Three questions were formulated to discuss these aspects. The first involves the photosensitizer properties and their performance against Gram positive and Gram negative bacteria. The second discusses the use of light sources in accordance with the dye maximum absorbance to obtain optimal results. The third looks at the relevance of photosensitizer concentration, the possible formation of self-aggregates, and light source effectiveness. This review demonstrated that some groups of photosensitizers may be more effective against either Gram positive or negative bacteria, that the light source must be appropriate for dye maximum absorbance, and that some photosensitizers may have their absorbance modified with their concentration. For the best results of PDT against the main cariogenic bacteria (Streptococcus mutans), a variety of aspects should be taken into account, and among the analyzed photosensitizer, erythrosin seems to be the most appropriate since it acts against this Gram positive bacteria, has a hydrophilic tendency and even at low concentrations may have photodynamic effects. Considering erythrosin, the most appropriate light source should have a maximum emission intensity at a wavelength close to 530 nm, which may be achieved with low cost LEDs.

On the observation of 2.8 μm emission from diode-pumped Er3+- and Yb3+-doped low silica calcium aluminate glasses

In this letter, we investigate the midinfrared photoluminescence of a series of diode-pumped Er3+-doped and Er3+, Yb3+-codoped low-silica content aluminosilicate glasses. Emission at 2.8 μm was observed in both single doped and codoped samples. The effect of Yb3+ codoping of the Er3+-doped samples was such that, for example, for a 2 wt % Er3+-doped, the photoluminescence yield at 2.8 μm was found to be roughly three times larger than that of the single 2 wt % Er3+-doped sample. This behavior was attributed to the efficient sensitization of Er3+ by Yb3+ in our oxide based host glasses. The results reported in this letter, together with the outstanding mechanical, chemical, and thermal properties of these glasses, suggest that rare-earth doped calcium aluminate glasses may become an attractive host for the development of solid state lasers operating in the midinfrared.

Pump-power-controlled luminescence switching in Yb3+/Tm3+ codoped water-free low silica calcium aluminosilicate glasses

Intense infrared-to-visible upconversion emissions in Tm3+∕Yb3+ codoped water-free low silica calcium aluminosilicate glasses have been obtained under excitation at 976nm. The results showed that as the pump power/intensity is increased, a reduction of up to one order of magnitude at the 800∕480nm emitted intensity ratio is observed; characterizing what can be denominated as luminescent switching. The physical origin of this switching is discussed and explained in terms of the tailoring of luminescent switchers to operate in a large range of pump powers, what could be used in the development of sensors and networks for optical processing and optical communications.

Nd2O3 doped low silica calcium aluminosilicate glasses: Thermomechanical properties

The effects of Nd2O3 doping on the thermal and mechanical properties of vacuum melted, low silica, calcium aluminosilicate glasses are presented. For the doped glasses, the vitrification limit was found to correspond to a maximum load of 5 wt % Nd2O3. The influence of the rare earth doping on the thermal diffusivity, thermal conductivity, and Vickers hardness was such that all these physical parameters decreased by roughly the same amount, namely 8%, between the undoped and the 5 wt % doped sample. The dependence of these parameters, as a function of the Nd2O3 doping, strongly supports the idea that the Nd3+ act as network modifiers.

Multiwavelength thermal lens determination of fluorescence quantum efficiency of solids: Application to Nd3+-doped fluoride glass

A multiwavelength thermal lens (TL) method was developed to determine the fluorescence quantum efficiency of solids. The experiments have been performed in Nd3+-doped fluoride glasses, using five different excitation wavelengths: 514, 576, 741, 796, and 867 nm. In this work, the absolute value of fluorescence quantum efficiency can be obtained by the linear dependence of the TL signal with the excitation wavelength. Our results suggest that the method can be applied to study a wide range of fluorescent materials, with a special ability to be used for measurements of highly transparent materials with very low TL effect.

Dynamics of reepithelialisation and penetration rate of a bee propolis formulation during cutaneous wounds healing.

The aim of this work is to investigate the dynamics of reepithelialisation and the penetration rate of a propolis ointment formulation during cutaneous wounds healing. The experiments were performed as a function of the treatment time in a well controlled group of rats. We observed that the propolis ointment influenced the healing process stimulating keratinocytes cell proliferation as compared to the control group. It was shown that the propagation of the bee propolis was dependent on the wound healing stages. In addition, the photoacoustic spectroscopy showed that the applied substances reached the deep wound region, highlighting once again the particular characteristic of this technique to evaluate the penetration rate of substances through the skin.

Time-resolved thermal mirror for nanoscale surface displacement detection in low absorbing solids

A time-resolved thermal mirror method for measurements of absolute thermo-optical-mechanical properties of low absorbing solids is presented. The thermoelastic equation for the surface displacement and an analytical expression for the probe beam intensity at the detector plane were derived. Experimental proofs were performed in an optical glass and the fitted parameters are in good agreement with previous literature data for thermal, optical, and mechanical properties, suggesting that the method is a useful tool for the characterization of a wide range of transparent materials.