Papers by Keyword: Optical Spectroscopy

Abstract: Single crystalline high quality α-Mn₂O₃ nanorods and sea-urchins assembled with pen-type nanoneedles have been successfully synthesized by template-free hydrothermal route. The variation in hydrothermal temperature has affected the morphology of the α-Mn₂O₃ sea-urchin assembled with the nanoneedles noticeably. The influence of temperature change on the thickness, crystallinity, surface morphology and optical properties of α-Mn₂O₃ has been characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) analysis, Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), Raman Spectroscopy (RS) and UV-visible Spectroscopy. The results showed that in our experimental conditions, single crystalline nanorods of the α-Mn₂O₃ were obtained at a low temperature of 180 °C, while single crystalline sea-urchin assembled with pen-type nanoneedles were obtained by increasing the temperature to 280 °C. Nanorods and sea-urchin assembled with pen-type nanoneedles obtained had the well defined morphology and crystalline quality. The sea-urchin synthesized at 280 °C exhibited more than 90% absorption in UV-visible spectrum.

Abstract: Principal possibility of the using of chalcogenide glasses (on the example of Ge₁₈As₁₈Se₆₄) as active media for temperature sensors is considered in this work. Differential scanning calorimetry testing of the investigated glasses shown that 2 years of natural storage does not lead to the drift of their DSC-parameters (glass transition temperature and endothermic peak area). Investigation of the temperature dependence of optical transmission spectra shows the linear character of optical band-gap changes with a temperature. Temperature sensitivity index β for Ge₁₈As₁₈Se₆₄ is estimated to be equal to the ~1.2·10^-3 eV/°C.

Abstract: The study of optical properties of Al₂O₃, SiO₂, TiO₂, and ZnO nanoparticles in weak optical fields is presented. We found that some nanoparticles have unique optical nonlinearity: The values of portions to nanoparticle refractive index and absorption coefficient increase to maxima, and then decrease to zero when the radiation intensity changes from 1 to 500 W/cm2. We estimated electron energy structures of nanoparticles and experimentally determined that such nonlinearity is directly related to peculiarities of the energy structure. We obtained a good fitting of theoretical results to the experimental ones (e.g. absorbance spectra of nanoparticles; the dependence of nanoparticle refractive index and absorption coefficient on radiation intensity).

Abstract: All over the world the investigations of nanophotonic structures called photonic crystals (PCs) are performed. These crystals have potential applications in optoelectronics, e.g. optical filters, antireflective surface coatings, lossless frequency selective mirrors. In Institute of Physics at Silesian Technical University the opal photonic crystals consisting of monodisperse spherical particles, that have diameters of several hundred nanometers, are produced using colloidal self-assembly technics. The main aim of this work is the comparison between pieces of information on morphology of photonic crystals that can be obtained from electron microscopy and from the angular characteristics of optical transmittance and reflectance. The morphology of the samples is characterized by scanning electron microscopy (SEM). Nanosphere diameters are established from statistical analysis of SEM images. The optical properties, which are determined by the photonic band structure, are studied by means of light transmission and reflection measurements. There is a relationship between the wavelength position of transmittance minimum or reflectance maximum and the diameter of the nanospheres. The size of nanospheres obtained from optical measurement results were compared with data obtained from SEM images.

Abstract: Electrical and optical character of nanostructured Cr_1-xV_xS₂ is studied here. This sulphide based nanoClusters (NC) was developed through chemical sol-gel route using (NH₄)₂Cr₂O₇ and NH₄VO₃ as active reagent and biopolymer gum acacia is used as capping agent. Core-shell NC has developed with sequential addition of active reagents in sulphation process. It is also possible to develop another type of core shell NC by reversal of the sequence of added reagents, i.e. interchanging the core and shell part. Experimental investigation including UV-VIS spectroscopy, dc current-voltage characteristics (CVC) have carried on. The results of CVC at room temperature (RT) show the distinctive features of localized energy levels. UV-VIS spectroscopic analysis shows absorption peak is blue shifted due to quantum confinement of nanoparticles. Overall appearance of optical absorption curve is completely different for two NCs. Peak positions are different for two types of core shell NC which confirms that the constituent materials of core and shell of two NC s has interchanged.

Abstract: Olivines are high-temperature materials in which divalent cations occupy two non-equivalent octahedral sites, M1 and M2. Cation redistribution processes between the M1 and M2 sites are fundamental steps for cation diffusion in olivines. We have performed temperature-jump relaxation experiments on both M1 and M2 sites in (CoxMg1-x)2SiO4 olivines by monitoring the time evolution of optical absorption of Co2+ ions on M1 and M2 sites. Results derived from the modeling of the experimental relaxation curves show that the kinetics of cation exchange is strongly temperature- and composition-dependent and that relaxation times for cation redistribution at about 1000 oC are less than 1 s. The activation energy of cation redistribution is about 2.0 eV.

Abstract: In this paper we report on a new optical technique to measure in situ the fraction solid during solidification. The technique utilizes the extreme properties of silica aerogels, being optically transparent in the visible and near infrared. From measured brightness time profiles the fraction solid can be derived using a suitable theoretical approach. The technique is tested on a technical AlSiMg alloy (A357) solidified directionally in the furnace facility Artemis. The results are compared with the well known theoretical expressions of the lever rule and the Scheil relation. The measured fraction solid as a function of temperature agrees well with model of Scheil which shows the capabilities of the new technique.

Abstract: Complex emission spectra of europium doped rare earth calcium oxoborates, EuCa4O(BO3)3 - EuCOB, and GdCa4O(BO3)3: Eu3+- GdCOB: Eu3+, were finely analyzed for better understanding of some local perturbations detected in these solid media. Highlighting a “size effect” of dopant / matrix ions, the interaction between the host lattice and the embedded ion is demonstrated. The evolution of the crystal field strength of R3+ ions along the rare earth series is presented for C-type RE2O3 oxides. According to R3+ - RE3+ ionic radii difference (R3+ for a dopant ion and RE3+ for a matrix ion), two opposite standings are evidenced along a series. Effect of high concentration doping on spectral line broadening is illustrated following a half-height width of 2P1/2 level of Nd3+ ion in A-type La2O3 oxide.

Abstract: We have studied effects of thermal treatment in vacuum and wet oxidation on the optical transmission of SiC samples with porous layer on the Si face in the visible and near infrared spectral range. An analysis of changes in the absorption coefficient shows that the process of graphitization in vacuum begins at a temperature below 700°C and can be observed at wet oxidation at 1000°C.