Fluorescence et processus de transfert dans K₂GdF₅ : Tb³⁺ ou Eu³⁺

Laboratoire de Chimie des Solides, URA 444 (CNRS), Université Blaise Pascal et ENSCCF, 63177 Aubière Cedex, France.

Résumé

Les transferts d'énergie de Gd³⁺ vers Tb³⁺ ou Eu³⁺ sont étudiés dans K2GdF5 en faisant varier la concentration en ions accepteurs entre 0 et 5 %. L'analyse des émissions, des excitations et des cinétiques de la fluorescence permet d'estimer les rendements et les probabilités de transfert et de proposer les mécanismes dominants dans les processus de transfert.

Abstract

A study of the energy transfer process from gadolinium to terbium or europium in K₂GdF₅ was performed for a 0-5 % range of acceptor concentrations. From measurements of fluorescence decay times, the energy transfer efficiencies and probabilities were derived. At 300 K and 77 K, excitation into the Gd³⁺ ion results in mainly Tb³⁺ or Eu³⁺ emission. It is shown that the excitation energy migrates among the Gd³⁺ sublattice before to be transferred to the Tb³⁺ or Eu³⁺ acceptor. The energy levels involved in the energy transfer and the mechanism of the transfer are discussed. Our results suggest that the Gd³⁺ (⁶P) → Tb³⁺ energy transfer occurs by a dipole- dipole mechanism while an exchange interaction is more likely at the origin of the Gd³⁺ (⁶p) → Eu³⁺ energy transfer.