Non-resonant energy transfer between Tb<sup>3+</sup> and Eu<sup>3+</sup> in the cubic hexachloroelpasolite crystals Cs<sub>2</sub>NaTb<sub>1-x</sub>Eu<sub>x</sub>Cl<sub>6</sub> (x=0.01-0.15)
M Bettinelli; C D Flint; M Bettinelli; Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, Padova Univ., Italy; C D Flint; Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, Padova Univ., Italy
Журнал:
Journal of Physics: Condensed Matter
Дата:
1990-10-22
Аннотация:
Luminescence decay curves have been measured for the Eu<sup>3+</sup> emission and Tb<sup>3+</sup> emission in the cubic crystals Cs<sub>2</sub>NaTb<sub>1-x</sub>Eu<sub>x</sub>Cl<sub>6</sub> at 80 and 293 K using pulsed dye laser excitation into the <sup>5</sup>D<sub>4</sub> state of Tb<sup>3+</sup> and the <sup>5</sup>D<sub>1</sub> state of Eu<sup>3+</sup>. For excitation of Tb<sup>3+</sup>, efficient energy transfer occurs to the <sup>5</sup>D<sub>0</sub> state (but not the <sup>5</sup>D<sub>1</sub> state) of Eu<sup>3+</sup> and there is fast energy migration within the <sup>5</sup>D<sub>4</sub> state. When excitation is into the <sup>5</sup>D<sub>1</sub> state of Eu<sup>3+</sup>, phonon-assisted coupling to the Tb<sup>3+</sup> ions results in enhanced relaxation to the <sup>5</sup>D<sub>0</sub> state but the lifetime of <sup>5</sup>D<sub>0</sub> is not affected by the presence of Tb<sup>3+</sup>. In all cases the non-resonant energy transfer involves creation or annihilation of phonons which have odd parity with respect to the metal centers and cannot be explained within the usual Born-Oppenheimer treatment of phonon-assisted energy transfer. The mechanism of the energy transfer processes is considered in detail.
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