Naira Maria Balzaretti

Pressure dependence of the refractive index of diamond, cubic silicon carbide and cubic boron nitride

Abstract The pressure dependence of the refractive index of diamond, cubic boron nitride and cubic silicon carbide, was measured up to 9 GPa by an interferometric method using the diamond anvil cell. A least-square fit yields the following values for ( 1 n ) ( d n d P ): − 3.6 × 10−4GPa−1 for diamond, −3.2 × 10−4GPa−1 for c-BN and, for 3CSiC, −8.3 × 10−4GPa−1. These results were used to investigate, for the first time under pressure, general empirical relationships between refractive index and energy gap found in the literature. The volume dependence of the electronic polarizability, α, of these compounds was determined through the Lorentz-Lorenz approach. The obtained linear behavior of α for the three cases was correlated to previous results for the pressure dependence of the transverse effective charge, e T ∗ .

FTIR analysis and evaluation of carcinogenic and mutagenic risks of nitro-polycyclic aromatic hydrocarbons in PM1.0.

Nitro-polycyclic aromatic hydrocarbons (NPAHs) represent a group of organic compounds of significant interest due to their presence in airborne particulates of urban centers, wide distribution in the environment, and mutagenic and carcinogenic properties. These compounds, associated with atmospheric particles of size < 1 μm, have been reported as a major risk to human health. This study aims at identifying the spectral features of NPAHs (1-nitropyrene, 2-nitrofluorene, and 6-nitrochrysene) in emissivity and transmittance spectra of samples of particulate matter < 1 μm (PM1.0) using infrared spectrometry. Carcinogenic and mutagenic risks of the studied NPAHs associated with PM1.0 samples were also determined for two sampling sites: Canoas and Sapucaia do Sul. The results showed that NPAH standard spectra can effectively identify NPAHs in PM1.0 samples. The transmittance and emissivity sample spectra showed broader bands and lower relative intensity than the standard NPAH spectra. The carcinogenic risk and the total mutagenic risk were calculated using the toxic equivalent factors and mutagenic potency factors, respectively. Canoas showed the highest total carcinogenic risk, while Sapucaia do Sul had the highest mutagenic risk. The seasonal analysis suggested that in the study area the ambient air is more toxic during the cold periods. These findings might of significant importance for the decision and policy making authorities.

Fluorescence properties of benzoxazole type dyes entrapped in a silica matrix by the sol-gel method

For the first time, the incorporation of 2,5-bis(benzoxazol-2′-yl)-4-methoxyphenol (BM) in a silica matrix by the sol–gel method has been accomplished, producing transparent and translucent monoliths with fluorescence properties. The intensity and wavelength range of the fluorescence bands F1 (primary structures) and F2 (proton-transferred forms) were extremely sensitive to the presence of solvents and to the dye concentration in the silica pores. The F2 band was observed when the silica pores contained solvent; however, after the solvent evaporation, the interactions of the dye with the silica host hindered the proton-transfer reaction, eliminating the F2 band and indicating the polar and acidic character of this host. Nevertheless, it was observed that the proton-transfer could be recovered after insertion of suitable solvents inside the matrix, like water, ethanol or DMF. Changes in the fluorescence spectra due to the use of different dye concentrations were observed when the monoliths were prepared with ethanol as solvent. During the aging process, the F2 band persists at high dye concentrations, but it disappears for low dye concentrations. The high sensitivity of the proton-transfer reaction of this dye in a particular environment, where the solvent and the host play important roles, suggests the possible application of this dye as a photoprobe for this kind of system.

High pressure loading of organic dyes into a silica matrix

Abstract High density, transparent and crack-free compacts of silica gel doped with naphthazarin, quinizarin and rhodamine 6G, were produced by sol–gel synthesis with high pressure at room temperature. Compacts are very stable, being resistent to polishing and leaching by ethanol and acetone. They show optical properties, as absorption and fluorescence, similar to those at dilute solutions, indicating that the dyes are dispersed in the silica matrix as individual molecules. Heat treatment to 150°C for 1 h led to almost no degradation.

Variation of the refractive index and polarizability of sapphire under high pressures

In this article we present the experimental results for the pressure variation of the refractive index of sapphire up to 16 GPa, obtained with an interferometric method, using the diamond anvil cell. In the range of hydrostatic pressures, up to about 12 GPa, the analysis of the results with the classic Lorentz–Lorenz approach provides a nearly linear relation between polarizability (α) and volume, corresponding to a constant strain polarizability parameter. For pressures above 12 GPa, there is a substantial nonlinear deviation, associated with nonhydrostatic effects inside the diamond anvil cell.

Pressure dependence of the refractive index and electronic polarizability of LiF, MgF2 and CaF2

Abstract The pressure dependence of the refractive index of LiF, MgF2 and CaF2 was measured up to 8 GPa using an interferometric method with the diamond anvil cell. Despite the different crystalline structures, a similar increasing behavior of n(P) for the three compounds under consideration was observed, indicating that the fluorine ion should have an important role in the volume dependence of the optical properties of these materials. The respective variations of the electronic polarizabilities were determined by the Lorentz-Lorenz approach and they are represented by the following Mueller parameters: for LiF, Λ0 = 0.65, for MgF2, Λ0 = 0.71 and for CaF2, Λ0 = 0.55. Some empirical models found in the literature relating to the electronic polarizability and the interatomic distance, were also examined but none of them adequately describe the observed behavior.

Volume dependence of the electronic polarizability of magnesium oxide

Abstract In this work, a study of the volume dependence of refractive index and electronic polarizability of MgO, under hydrostatic pressure up to 10 GPa, is presented. The experimental results obtained show a decrease of the refractive index with pressure, and enable the calculation of the change of the polarizability a with volume V. The classical Lorentz-Lorenz approach describes well the results and gives a linear dependence between a and V. The results in the whole pressure range yielded a constant Mueller parameter of 1.28, that is in good agreement with a previous work in the low pressure range.

High pressure annealing of CVD diamond films

CVD diamond films were annealed from 600 to 1900 °C at 7.7 GPa in a toroidal high pressure (HP) apparatus, always inside the diamond-phase stability region. The annealed films were analyzed by Raman and infrared (IR) spectroscopy and the results showed that the diamond grains remained stable while the non-diamond carbon phases and impurities, responsible for the intricate film structure, changed after processing. For the HP annealing from 600 to 1300 °C, there were no major changes in the Raman spectra of the film, however, the film became easily broken and the IR spectra indicated a high reactivity of carbon with chemical elements from the environment. After annealing at 1500 °C and 7.7 GPa, the formation of diamond-like (DLC) and graphitic structures in-between the diamond grains were observed, while the reaction with the environment elements decreased. For higher temperatures, the DLC and graphitic structures persisted up to 1700 °C and the film incorporated OH in large amounts. The results showed that the non-diamond carbon species are susceptible to the HP annealing, and structural modifications in between the diamond grains are significant for temperatures above 1300 °C at 7.7 GPa.

High-Pressure Entrapment of Rhodamine 6G into a Silica Matrix

The entrapment of organic dyes with interesting optical properties in silica produced by sol-gel method, has been studied over the last years, aiming to obtain a new class of optical materials. The monoliths produced by this method present cracks, large shrinkage during the silica gelation and drying, and a great porosity, which decreases their optical performance. In a previous work, to overcome these difficulties, a high pressure (4.5 GPa) technique at room temperature was used to produce compacts of silica gel doped with rhodamine 6G (R6G). In this work, we extended this study to pressures up to 7.7 GPa to verify the effect of high pressure in the fluorescence spectra of the R6G and in the density and hardness of the compacts. High density (98% of the silica density), transparent and crack-free compacts were produced, being resistent to polishing. The fluorescence spectra were similar to the ones observed in ethanol solutions. These new class of materials are potentially useful for optical applications.

High pressure annealing of defects induced by ion implantation on graphite

Abstract The aim of this work was to investigate, by Raman spectroscopy, the effect of high pressure on the annealing of the surface disorder induced by hydrogen, carbon and nickel ion implantations on graphite samples. In the case of H implantation, the induced disorder decreased after annealing at 650°C for 7.7 GPa. For C implantation, the defect annealing started at 500°C for 7.7 GPa, while in the case of Ni implantation, it started at 850°C for the same pressure. For the three cases studied, there was practically no annealing effect for temperature treatments in vacuum up to 1100°C. The results indicated that high pressure plays an important role in the defect annealing, accelerating the graphitization process, probably due to the large volume of the defective ion implanted phase. Despite the annealing at high pressure being conducted deep inside the thermodynamic region of stability of diamond, the graphite phase was recovered, indicating that the nucleation barrier for diamond is indeed very high as compared to graphite.