RESUMO
The electrical conductivity of Na2O substituted zinc borate glasses has been studied in the frequency range of 10 mHz to 1 MHz and in the temperature range from 313 to 573 K. The conduction mechanism has been ascertained using the values of the frequency exponent (s) extracted from the fitting of experimental data of the real part of electric conductivity in light of the Almond-West equation. Depending on the glass composition, the ac conduction in the glasses happened via correlated barrier hopping and non-overlapping small polaron tunneling conduction models. The electric modulus studies support the assertion of composition dependent conduction mechanisms. Furthermore, electronic conduction and ionic conduction have been studied from impedance investigations. Equivalent circuit models were used to fit the Nyquist and Bode plots of each sample at the temperatures under consideration. It has been found that the activation energy values calculated from conductivity, electric modulus, and impedance measurements are more or less the same.
RESUMO
Dy3+ doped calcium aluminum borosilicate (CABS) glasses have been synthesized via quick melt quench technique. CABS: xDy3+ glasses (x = 0.1, 0.5, 1, 1.5 and 2 mol%) were subjected to various morphological and photoluminescence studies. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy were conducted to study the structural and bonding nature of the undoped glass. The excitation spectra of Dy3+ doped CABS glasses under 574 nm emission show many sharp peaks amongst which the transition from 6H15/2 â 6P7/2 (351 nm) had the highest intensity. Under 351 nm excitation, glasses exhibit sharp peaks in the blue, yellow and red regions corresponding to the transitions 4F9/2 â 6H15/2, 6H13/2, 6H11/2 and 6H9/2 respectively. The dipole-dipole nature of the interaction between the Dy3+ ions is confirmed via Dexter theory and Inokuti-Hirayama (I-H) model. CIE coordinates estimated from the emission profiles of these glasses under 351 nm excitation fall in the white region. Considering that these glasses exhibit sharp visible emission under UV excitation, have stable yellow to blue (Y/B) ratios and fast decays with intense energy transfers, we propose to utilise these glasses for white light generation and other white light LED (w-LED) and solid-state lighting (SSL) applications.
RESUMO
With an intend to develop white light emitting phosphor, for w-LED application, a series of dysprosium (Dy3+) doped novel Na3Ba2LaNb10O30 phosphors were prepared using solid state reaction technique at 1300 °C. Their structural, morphological and vibrational spectroscopic analysis was performed. We illustrate the luminescence characteristics of the prepared phosphors for various Dy3+ ion doping concentration. The XRD analysis demonstrates that the prepared phosphors were in single phase, and of tetragonal tungsten bronze structure of the P4bm space group. The FE-SEM image reveals that the prepared phosphors contained irregular shaped both nano and micro particles. Under near-ultraviolet (n-UV) irradiation at 387 nm, the photoluminescence (PL) emission spectra shows three characteristic bands at 481 nm (blue), 575 nm (yellow) and 666 nm (red). Obtained optimized Dy3+ ion concentration for the prepared sample is 7.0 mol%, beyond which the concentration quenching begins. Bonding between Dy-O is covalent in nature as confirmed by bonding parameters and the Dexter theory revealed that the energy transfer among Dy3+ ions is dipole-diploe interaction. CIE chromaticity coordinates, CCT and color purity confirms the formation of warm white light emitting phosphors. Lifetime analysis demonstrates the longer decay time in the phosphors. The Internal Quantum Yield (IQE) and brightness (B) for the optimised phosphor is calculated as 45.35% and 11.41% respectively, which makes it a suitable phosphor for w-LED.
RESUMO
AIM: The aim of this study is to investigate the effect of scattering and differential attenuation on dose profile of 6 MV photon beam in the presence of cadmium (Cd)-free compensator which has been used in compensator-based intensity-modulated radiotherapy. MATERIALS AND METHODS: Totally, 10 slabs of Cd-free compensator having thicknesses ranging from 2.4 to 61.4 mm have been prepared. Dose profiles have been taken using computer-controlled radiation field analyzer for five field sizes from 30 mm × 30 mm to 200 mm × 200 mm and at three depths in water phantom. Off-axis dose variation (ODV) has been measured with off-axis percentage depth dose scan and with ion chamber by measuring point dose at two diagonal points with respect to dose at central axis point in a plane and at three depths. RESULTS: A decrease in beam flatness has been observed with increase in compensator thickness and depth in phantom. ODV has been found to increase with compensator thickness. Selective beam hardening has been observed due to differential attenuation from compensator. Point dose measurements show approximately 20% and 23% underdose region at 70 and 106 mm off-axis diagonal point, respectively, as compared to dose at central axis point for a field size of 200 mm × 200 mm at a depth of 15 mm, with 30.2-mm slab thickness. Significant increase in scattered penumbra has been observed with field size and thickness of compensator due to increase in scattered photon. CONCLUSIONS: The presence of compensator changes photon beam mean energy along the cross-section resulted in decreased beam flatness and increased scattering. This may lead to overestimation of dose along off-axis within radiation field if change in flatness is not taken into account and more exposure to healthy tissues in penumbral region due to large-angle scattering.
