Tm-Yb-Tm energy transfers and effect of temperature on the fluorescence intensities in oxyfluoride tellurite compounds
G Ozen; J -P Denis; M Genotelle; F Pelle; G Ozen; Lab. de Physico-Chimie des Mater., CNRS, Meudon, France; J -P Denis; Lab. de Physico-Chimie des Mater., CNRS, Meudon, France; M Genotelle; Lab. de Physico-Chimie des Mater., CNRS, Meudon, France; F Pelle; Lab. de Physico-Chimie des Mater., CNRS, Meudon, France
Журнал:
Journal of Physics: Condensed Matter
Дата:
1995-05-29
Аннотация:
Up-conversion processes in PbF<sub>2</sub>+TeO<sub>2</sub>+WO<sub>3</sub> glass-ceramics doped with Tm<sup>3+</sup> and codoped with Tm<sup>3+</sup> and Yb<sup>3+</sup> ions were investigated under 680 nm excitation. Emission, excitation and time-resolved spectra and decay profiles were measured at temperatures between 12 and 300 K. A strong blue emission centred at 478 nm originating from the <sup>1</sup>G<sub>4</sub> level of Tm<sup>3+</sup> was observed in a doubly doped sample via a two-step energy transfer mechanism, (Tm) <sup>3</sup>F<sub>4</sub> to (Yb) <sup>2</sup>E<sub>5/2</sub> energy transfer and a positive feedback (Yb) <sup>2</sup>F<sub>5/2</sub> to (Tm) <sup>1</sup>G<sub>4</sub> process, raising the excited Tm<sup>3+</sup> ion from the <sup>3</sup>F<sub>4</sub> to the <sup>1</sup>G<sub>4</sub> level following the absorption of 680 nm excitation light. The time-resolved emission spectra prove the validity of these energy transfer processes. The optical properties of the excited levels and the energy transfer processes involved in the up-conversion were interpreted using a kinetic model describing the interactions between rare-earth ions in terms of energy migration and luminescence quenching. The microscopic interaction parameter for Tm-Tm intersection in the absence of Yb<sup>3+</sup> ions was determined to be 6.1*10<sup>-40</sup> cm<sup>6</sup> s<sup>-1</sup> in the sample having 1.0 mol% TmF<sub>3</sub>. The same parameter for the energy transfer from Tm to Yb was calculated to be 1.2*10<sup>-38</sup> cm<sup>6</sup> s<sup>-1</sup> in the sample having 0.15 mol% TmF<sub>3</sub> and 15 mol% YbF<sub>3</sub>. No effect of temperature on the emission intensity of the (Tm) <sup>3</sup>F<sub>4</sub> level was observed although the emission intensities of the (Tm) <sup>1</sup>G<sub>4</sub> and (Yb) <sup>2</sup>F<sub>5/2</sub> levels were decreased with increasing temperature. The former decrease accounts for the migration of energy between Yb<sup>3+</sup> ions and controls the temperature dependence of the blue-up conversion emission.
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