Influence of annealing on X-ray diffraction of natural alexandrite
In this work we present results of X-ray diffraction using powder method, on natural alexandrite samples from Minas Gerais State (Brazil), as a function of a sequence of annealing. From these measurements we determine lattice parameters before (a=9.405 Å, b=5.471 Å, c=4.409 Å) and after annealing, and its structure is confirmed as orthorhombic. Measurements done after an annealing of 15 minutes at 700 °C and for 5 hours at 1000 °C indicate the migration of atoms present in the sample through different phases, which were also identified by Microprobe Analysis (WDS). However we have verified that such migration does not modify the structure. X-ray diffraction measurements have been carried out in conjunction with optical absorption in the UV–Vis as a function of annealing.
The electric field gradient in natural iron-doped chrysoberyl Al2BeO4 and sinhalite MgAlBO4 single crystals
This work reports on the evaluation of the electric field gradient (EFG) in natural chrysoberyl Al2BeO4 and sinhalite MgAlBO4 using two different procedures: (1) experimental, with single crystal Mössbauer spectroscopy (SCMBS) on the three principal sections of each sample and (2) a “fully quantitative” method with cluster molecular orbital calculations based on the density functional theory. Whereas the experimental and theoretical results for the EFG tensor are in quantitative agreement, the calculated isomer shifts and optical d–d-transitions exhibit systematic deviations from the measured values. These deviations indicate that the substitution of Al and Mg with iron should be accompanied by considerable local expansion of the coordination octahedra.
Simulating the Illuminance and Efficiency of the LEDs Used in General Household Lighting
Abstract The advantage of the LEDs illumination in general household lighting was proposed. High efficiency white LED as the light source was provided the energy saving illumination of the general household lightings. Different spaces in general household with different standards of average illuminance were designed and simulated by LightTools and DIALux software. The power consumptions and efficiency of traditional illuminated light sources and LED light source in lighting the household environment were analyzed and compared with each other at the same standard of average illuminance. Finally, it provided the advantage of using white LEDs in different spaces of the general household lighting.