Evaluation of TeO2 content on the optical and spectroscopic properties of Yb3+-doped calcium borotellurite glasses.

This paper reports the synthesis and the characterization of Yb3+-doped calcium borotellurite (CaBTeX) glasses with composition 10CaF2-(29.5-0.4x)CaO-(60-0.6x)B2O3-xTeO2-0.5Yb2O3 (x=10, 16, 22, 31 and 54mol%). The results of XRD confirm the amorphous character of all the samples. The density, molar volume, refractive index and electronic polarizability values show an increase with TeO2 content. Otherwise, the optical band gap energy shows a decrease with the increase of TeO2 content. The replacement of CaO and B2O3 by TeO2 changes the glass structure, which decreases the excited Yb3+/cm3 and, consequently, the luminescence intensity. The temperature dependence of luminescence was studied for all the samples up to 420K. The fluorescence lifetime does not change significantly due to TeO2 addition. In addition, absorption and emission cross section were calculated and present high values as compared to other tellurite and phosphate glasses.

In situ structural analysis of calcium aluminosilicate glasses under high pressure.

In situ micro-Raman spectroscopy was used to investigate the structural evolution of OH(-)-free calcium aluminosilicate glasses, under high pressure and at room temperature. Evaluation was made of the role of the SiO2 concentration in percalcic join systems, for Al/(Al + Si) in the approximate range from 0.9 to 0.2. Under high pressure, the intensity of the main band related to the bending mode of bridging oxygen ([Formula: see text][T-O-T], where T = Si or Al) decreased gradually, suggesting that the bonds were severely altered or even destroyed. In Si-rich glasses, compression induced a transformation of Q (n) species to Q (n-1). In the case of Al-rich glass, the Al in the smallest Q (n) units evolved from tetrahedral to higher-coordinated Al (([5])Al and ([6])Al). Permanent structural changes were observed in samples recovered from the highest pressure of around 15 GPa and, particularly for Si-rich samples, the recovered structure showed an increase of three-membered rings in the Si/Al tetrahedral network.

The phase-resolved photoacoustic method to indicate chemical assignments of paracetamol.

In this work, the phase-resolved photoacoustic method was applied to provide specific information on the chemical assignments of paracetamol in the near-infrared region. Two broad bands, centered at 1370 and 1130 nm, were well-resolved using this method, making it possible to assign the peaks centered at 1398, 1355 and 1295 nm to a C-H combination from a CH3 structure and the peak at 1305 nm to a C-H combination from the aromatic ring. This information represents a new finding in chemical studies regarding this medicament.

Soret effect and photochemical reaction in liquids with laser-induced local heating.

We report a theoretical model and experimental results for laser-induced local heating in liquids, and propose a method to detect and quantify the contributions of photochemical and Soret effects in several different situations. The time-dependent thermal and mass diffusion equations in the presence and absence of laser excitation are solved. The two effects can produce similar transients for the laser-on refractive index gradient, but very different laser-off behavior. The Soret effect, also called thermal diffusion, and photochemical reaction contributions in photochemically reacting aqueous Cr(VI)-diphenylcarbazide, Eosin Y, and Eosin Y-doped micellar solutions, are decoupled in this work. The extensive use of lasers in various optical techniques suggests that the results may have significance extending from physical-chemical to biological applications.

Preparation, characterization, and spectroscopic properties of PC/PMMA doped blends: study of the effect of rare-earth doping on luminescence, quenching rate, and lifetime enhancement.

Optical properties of highly transparent blends formed by bisphenol A polycarbonate (PC) and poly(methyl methacrylate) (PMMA) and doped with either europium(III) thenoyltrifluoroacetone hydrate [Eu(TTA)(3)-hydrate] or terbium(III) acetylacetonate hydrate [Tb(ACAC)(3)-hydrate] were studied. From the absorption/emission spectra (200 to 800 nm), percolation limits of less than 0.4 wt/wt% for Eu and above 0.7 wt/wt% for Tb were found. Lifetimes for 20/80 and 60/40 Tb-doped blends were from 1.0 to 1.5 ms, respectively, about 5 times longer than for a similar blend prepared with Langmuir-Blodgett film. For blends doped with Eu, the lifetimes were from 0.4 to 0.8 ms, almost double that for the pure complex. The results indicated interactions between the PC/PMMA blends and the rare-earth ion complex. Particularly, photoluminescent spectra evidenced the incorporation of the Eu(3+) and Tb(3+) ions into the blend, with quenching observed near 1.0 wt/wt%, except for the 20/80 blend doped with Eu ion, in which luminescence increased to 5 wt/wt %.

High values of gain cross section and luminescence quantum efficiency in OH(-)-free Ti3+-doped low-silica calcium aluminosilicate glass.

We recently reported that Ti(3+)-doped low-silica calcium aluminosilicate glass presents long luminescence lifetime (170 micros) and broad emission band (190 nm) shifted toward the visible region when compared with those from Ti(3+):sapphire single crystal and Ti(3+)-doped glasses [Phys. Rev. Lett.100, 027402 (2008)]. Here we demonstrate that this glass also shows high values of both gain cross section (approximately 4.7 x 10(-19) cm(2)) and luminescence quantum efficiency (approximately 70%). By comparing these values with those for Ti(3+):sapphire crystal, we can conclude that the studied Ti(3+)-doped glass is a promising system for tunable solid-state lasers.

Photoacoustic spectroscopy as a tool for determination of food dyes: comparison with first derivative spectrophotometry.

Photoacoustic spectroscopy (PAS) was applied as a method to quantify dyed food samples, and was compared with First Derivative Spectrophotometry (FDS). The dyes Brilliant Blue (B), Sunset Yellow (S) and Tartrazine (T), which are common food additives, were employed for the comparisons. Polyester-type Polyurethane (PU) foam was used for extraction of the dyes from a solution containing the food matrix. For the spectrophotometric determinations, the adsorbed dyes were recovered by using dimethylformamide. The PAS measurements were carried out directly on the PU foam. The PAS method showed greater sensitivity, with detection limits of 0.028 mg L(-1) and 0.086 mg L(-1) for S and T, respectively, in the S+T mixture, and of 0.012 mg L(-1) and 0.068 mg L(-1) for B and T, respectively, in the B+T mixture. The values of relative error obtained for all the dyes were small: approximately 0.3-3.6% for the spectrophotometer, and approximately 0.1-2.9% for the PAS method. The PAS technique can be applied to the determination of the selected dyes in commercial food products, with some advantages: it reduces the number of analysis steps, it is a "green" method with less chemical waste, a minimal sample amount is needed, and it is non-destructive.

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 study of photochemical reaction kinetics.

We consider the time dependence of the absorption coefficient due to the photoinduced chemical reaction (PCR) and species diffusion to calculate the temperature rise in the thermal-lens (TL) effect. The TL signal at the detector plane is also calculated. This theoretical approach removes the restriction that the PCR time constant is much greater than the characteristic TL time constant, which was assumed in a previously published model. Hydrocarbon fuel and aqueous Cr(VI) samples are investigated, and quantitative experimental results for the thermal, optical, and PCR properties are obtained. While similar results were obtained for the Cr(VI) solution using the previous and present models, the relative difference between the PCR time constants extracted from the same experimental data for a hydrocarbon fuel sample is found to be more than 220%. This demonstrates the significant difference of the two models.

A study of pressure and chemical substitution effects on the magnetocaloric properties of the ferromagnetic compound UGa(2).

We report on pressure effects on the magnetic and magnetocaloric properties of the compound UGa(2). Using a mean field approximation, we were able to calculate the isothermal entropy change and the adiabatic temperature change. Neither the applied pressure nor the chemical substitution experiments within the ranges studied revealed a remarkable improvement on the magnetocaloric effect (MCE) except for the Al substitutions. Nevertheless, we found that mechanical pressure and chemical pressure are equivalent in terms of the Curie temperature shift when Al, Ge and Si are substituted for Ga, but a different behavior is found when Ni, Fe and Co are used. Our results also show that a composite to operate between 80 and 120 K can be obtained using different concentrations of U(Ga,Ni)(2).

Thermal lens and interferometric method for glass transition and thermo physical properties measurements in Nd2O3 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.

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.

Statistical design of experiments: study of cross-linking process through the phase-resolved photoacoustic method as a multivariable response.

This work presents an add-on result of cross-linking using photoacoustic spectroscopy (PAS) phases in a multivariable process using the phase-resolved photoacoustic (PRPA) method. The method is tested to separate contributions from groupings -OH, -CH(2)-, -CH(3), and Si-OH overtones in the range from 700 to 2600 nm. Samples of the copolymers ethylene vinyltrimethoxysilane (EVS) and grafted vinyltrimethoxysilane (VTS) on low-density polyethylene (LDPE) were prepared having concentrations (C) of 3, 5, and 7% of catalyst and temperatures (T) of 70, 80, and 90 degrees C. By considering the condensation reaction, the reduction of -OH groups is monitored. The PRPA analysis was carried out using the surface response methodology and results indicated the optimum point for both answers (signal and phase-resolved) and for both factors of interest (C, T). For the copolymers, it was found that C approximately (5.00 +/- 1.14)% and T approximately (82.4 +/- 4.3) degrees C, while for grafted LDPE PE(g) it was found that C approximately (4.92 +/- 0.85)% and T approximately (80.8 +/- 2.5) degrees C. These results agreed with the chemical analysis for gel content, which showed as the optimum point 5% of catalyst and temperature of 80 degrees C. Further, it is an advantage that the photoacoustic method allows one to per- form a nondestructive analysis.