Phan Van Do

A bright yellow light from a Yb3+,Er3+-co-doped Y2SiO5 upconversion luminescence material

A bright yellow light from Yb3+ and Er3+ doped Y2SiO5 upconversion materials in particle and fiber form were prepared by a co-precipitation, and electrospinning method. The morphologies of the prepared samples were investigated through FT-IR, FE-SEM, XRD and Raman measurements. The upconversion properties of the samples are carefully studied based on the absorption, fluorescent and decay time measurements. Under 980 nm excitation, the prepared material shows bright yellow emission. By controlling the concentration of Yb3+ or Er3+ and the excitation laser power, the ratio of red to green emission intensity can be varied to adjust the color tuning properties of the phosphor. The upconversion mechanism, and transition probabilities were elucidated owing to Judd–Ofelt theory. The radiative quantum efficiencies for the red (4F9/2) and green (4S3/2) bands were estimated to be 87% and 55%, respectively. The color coordinates of the system were evaluated as a function of the dopant concentrations and plotted on a standard CIE index diagram. The change of band intensity ratio with dopant concentrations gives a promising potential of the current phosphor for lighting application.

A fractal model for streaming potential coefficient in porous media: Fractal model for streaming potential

Streaming potential is the result of coupling between a fluid flow and an electric current in porous rocks. The modified Helmholtz–Smoluchowski equation derived for capillary tubes is mostly used to determine the streaming potential coefficient of porous media. However, to the best of our knowledge, the fractal geometry theory is not yet applied to analyse the streaming potential in porous media. In this article, a fractal model for the streaming potential coefficient in porous media is developed based on the fractal theory of porous media and on the streaming potential in a capillary. The proposed model is expressed in terms of the zeta potential at the solid−liquid interface, the minimum and maximum pore/capillary radii, the fractal dimension, and the porosity of porous media. The model is also examined by using another capillary size distribution available in published articles. The results obtained from the model using two different capillary size distributions are in good agreement with each other. The model predictions are then compared with experimental data in the literature and those based on the modified Helmholtz–Smoluchowski equation. It is shown that the predictions from the proposed fractal model are in good agreement with experimental data. In addition, the proposed model is able to reproduce the same result as the Helmholtz–Smoluchowski equation, particularly for high fluid conductivity or large grain diameters. Other factors influencing the streaming potential coefficient in porous media are also analysed.

The studies of energy transfer between Sm3+ ions in lead sodium telluroborate glasses using Inokuti-Hirayama model

Lead sodium telluroborate (LSTB) glasses doped with different concentrations of Sm3+ ions were prepared by melting method. The excitation, emission spectra and lifetimes of LSTB:Sm3+ have been investigated. The quenching of luminescence intensity happens after 0.75 mol% concentration of Sm3+ ions. The non-exponential decay curves are fitted to the Inokuti and Hirayama model to give the energy transfer parameters between Sm3+ ions. The dominant interaction mechanism for energy transfer process is dipole–dipole interaction. The energy transfer probability (WDA) increases whereas lifetime (τexp) decreases with the increase of Sm3+ concentration in glass.

Optical properties of Eu3+ ions in boro-tellurite glass

The excitation, emission spectra and and lifetime of Eu-doped borotellurite glasses (BTe) have been investigated. The sideband phonon energy and electron-phonon coupling strength ( g ) have been found. The intensity parameters Ω λ were calculated from the emission spectrum. These parameters were used to predict radiative properties such as transition probabilities ( A R ), calculated branching ratios ( β R ) and stimulated emission cross-sections ( σ λp ) for 5 D 0 → 7 H J H F J transitions.