Papers by Keyword: Optical Spectra

Abstract: A set of nonlinear equations about the band gap and the index n of material property with the absorptance, reflectance and transmittance were produced based on Tauc relation. Optimizing fitting the experimental spectroscopy data, such as absorption, reflection and transmission, the band gapand the index n related to the material property could be obtained accurately and reliably. Meanwhile, the experimental data were used as more as possible, and the artificial errors at pre-determining the index n were avoided. The lowest correlation coefficient and the largest average relative error between the experimental and the calculated data are 0.9588 and 2.7% in all considered cases respectively. The best results show the band gap obtained from this method is more accurate, easier and faster than traditional extrapolation. Hence, this work would promote the precision and reliability for predicting the band gap and index of materials naturally.

Abstract: In this work, effects of Ni²⁺ ions on soda lime silicate glasses have been investigated. Glasses were prepared in formula (65-x)SiO₂ : 25Na₂O : 10CaO: xNiO (where x is 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10 mol%). The densities of glasses not depend on Ni²⁺ concentration. The refractive indices decreased with increasing of NiO concentration. The optical absorption spectra were measured by uv-visible spectrophotometer and show peaks correspond with Ni²⁺ in glass matrices. Both of octahedral transitions and tetrahedral transition from Ni²⁺ ion were found around 450 and 625 nm respectively. The color of glasses were also measured in CIE L* a* b* system.

Abstract: We present the results of the study of middle infrared absorption (MIR) and X-ray absorption (XAS) spectra of nanostructured CuO and Cu₂O ceramics prepared by the high pressure torsion method from coarse-grain oxide powders. We have found that the MIR bands at ~140 meV in CuO and Cu₂O nanoceramics are associated with the presence of Cu⁺ and Cu²⁺ ions, respectively. X-ray absorption spectra indicate an appearance of extra Cu²⁺ and Cu⁺ ions in nanoCu₂O and nanoCuO ceramics, respectively.

Abstract: Barium-bearing glass samples were fabricated in a laboratory scale using quartz sands that was a by-product of feldspar floatation in Tak Province, northern Thailand, and 30-wt% barite from Loei Province, northeastern Thailand, as the main compositions. Cr2O3 of concentrations ranging from 0.01 to 5.0 wt% was doped into the glass mixture. The dried powders were wellmixed in a ceramic crucible and melted in an electric furnace at 1250°C for 6 hr. Bubble-free glass samples were yielded after cooling down. The glass colors were changed from colorless to green by the addition of Cr2O3. Dielectric property, color, specific gravity, and refractive index of the glass samples were analyzed. It was found that dielectric constant, specific gravity, and refractive index increased with increasing amount of Cr2O3 dopant. Measurements of UV-VIS-NIR spectra and microstuctural analysis using scanning electron microscope were also carried out and discussed.

Abstract: Optical properties of bilayer organic light-emitting diodes (OLEDs) based on MEH-PPV (2-methoxy, 5-(2′-ethyl-hexoxy)-1,4-phenylene vinylene) and Alq3 (tris(8-hydroxy-quinolinato) aluminum) are investigated in this paper. Numerical method solving 1D model based on driftdiffusion, continuity and Poisson`s equations extended by boundary conditions in treatment of internal organic interface is applied. The obtained space charge densities were employed in the emissive singlet exciton continuity equation resulting in the singlet exciton distribution and the emission zone profile. Dipole methods were utilized for the simulation of light emission in a layered medium. The electroluminescence (EL) spectra of OLED are considered by taking into account dominant interference effects. The exciton quenching near electrodes, allowing for a dominant nonradiative decay, is treated through effective emission zone narrowing.