Papers by Author: P. Aschehoug

Abstract: In this work, Eu3+-doped CdS nanocrystals embedded in a SiO2 matrix were synthesised by a sol-gel method since this method confers a great chemical homogeneity, and allows in-situ generation and controlled growth of CdS nanocrystals within the silica glass. The influence of the sol-gel conditions on the Eu3+ optical response has been investigated. The synthesis conditions can be varied to modify the structure of the material, and the dispersion of the rare earth ion, within the silica matrix. From the optical analysis an energy transfer appears from CdS nanoparticles to Eu3+ ions but also a back transfer Eu3+ to CdS nanoparticles is evidenced.

Abstract: In view of the improvement of luminescent intensity in classical phosphors, different new techniques of synthesis have been developed. One of them is the sol-gel technique for nanopowder synthesis. Applied to a binary system Gd2O3-SiO2 doped with trivalent europium ion, very fine powder form samples have been obtained. In that case the emission intensity of 5D0→F2 electronic transition of 4f6 configuration is greatly enhanced compared to the bulk oxide. The lifetime measurements are given too. The size of nanoparticles is of about 10 nm, determined by dynamic light scattering and XRD analysis.

Abstract: Tungsten-phosphate glasses doped with trivalent europium ion are synthesized and their spectroscopic properties are analyzed. Following the evolution of the 5D0 → 7F1 electronic transition in a series of various glass compositions via two rank crystal field parameters (cfp’s), a slight modification of the local symmetry is evidenced in the series. Decay lifetimes of 5D1 and 5D0 levels are also analyzed. Optical properties clearly correspond to Eu3+ in the glassy phase. At room as well as at liquid nitrogen temperatures, the emission spectra display comparable features with prominent 5D0 → 7F2 transition. However, at 77 K, the maximum 7F1 splitting exhibits an increase of ≈ 20-23 % for all compounds. This increase is directly connected to a change in local environment around the rare earth ion. The optical properties and the crystal field variation could be correlated with the shortness of the metal-oxygen distances produced by the pressure when cooling.