M.A. Couto dos Santos

Intensity parameters of 4f—4f transitions in the Eu(dipivaloylmethanate)3 1, 10-phenanthroline complex

Abstract We present and discuss experimental and theoretical relevant intensity parameters of 4f—4f transitions in the Eu(dipivaloylmethanate) 3 1, 10-phenanthroline complex which is a highly luminescent material under UV excitation. The theoretical analysis is based on the crystallographic data of the compound and on a theoretical scheme which takes into account the forced electric dipole and dynamic coupling mechanisms as developed in previous work. The good agreement found between theory and experiment provides support to the model used and indicates that, at least in the present case, further contributions to the intensities beyond the second-order theory are of no relevance.

Theoretical analysis of the fluorescence yield of rare earth ions in glasses containing small metallic particles

We examine the fluorescence yield of rare earth ions in glasses containing a uniform volumetric distribution of metallic particles with small specific volume. The role of energy transfer between the ions and the particles is discussed. Depending on the particle size and the ion emission quantum efficiency, quenching or enhancement of the fluorescence is predicted.

Predicting the spectroscopic behaviour of Eu3+ in BaLiF3 via defect modelling and crystal field parameter calculations

Abstract The solution of Eu 3+ ions in BaLiF 3 is analysed through a defect simulation technique. The new relaxed positions of the nearest neighbour fluoride ions with respect to the central Eu 3+ ion are used to calculate the crystal field parameters. The set of non-zero crystal field components shows that the symmetry of the central ion is C 2h . The Eu 3+ ion dissolved in the matrix is thus generating a new site with a symmetry not usually found in the perovskite family. This explains the observed emission characteristics of the Eu 3+ ion that have been recently reported. It was found that the solution energy for Eu 3+ in the BaLiF 3 matrix is highly positive, indicating that the substitution of the Eu 3+ at the Ba 2+ site has a low probability, this latter result explaining why the observed emission intensities are weak.

Photoionization cross-section of isotropic defects or impurity centers in isolators

An analytical expression to calculate the photoionization cross-section of isotropic defects or impurity centers is being proposed by using the time-dependent perturbation theory. The ground-state wave function of the electron captured in the impurity state is described by a three-dimensional isotropic harmonic oscillator and the electron excited state in the continuum conduction band is described by a plane wave. The expression has been obtained considering all multipoles terms in the Hamiltonian, and that the radiation field which interacts with electrons is semi-classical and linearly polarized. This approximation is assumed because the effects of the linear contribution are dominant. The available data of the Al2 O3 :C and Lu2 SiO5 :Ce systems are in good agreement with our predictions. Such satisfactory comparison is a strong indication that the present model can be used to provide good predictions of the photoionization cross-section in several areas.