Studies
of Terbium Bridge: Saturation Phenomenon,
Significance of Sensitizer and Mechanisms of Energy Transfer, and
Luminescence Quenching
- Publication date
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Abstract
Terbium chain in the form of S →
(Tb<sup>3+</sup>)<sub><i>n</i></sub> → A (S = Ce<sup>3+</sup> or Eu<sup>2+</sup>, A = Eu<sup>3+</sup>), as a promising
energy transfer (ET) approach,
has been proposed to enhance Eu<sup>3+</sup> emission for solid-state
lighting. However, the viewpoint of ET from S to A via the terbium
chain (Tb<sup>3+</sup>–Tb<sup>3+</sup>–Tb<sup>3+</sup>–...) is very doubtful. Here, hosts of Ba<sub>3</sub>Ln(PO<sub>4</sub>)<sub>3</sub>, LnPO<sub>4</sub>, LnBO<sub>3</sub>, and Na<sub>2</sub>Ln<sub>2</sub>B<sub>2</sub>O<sub>7</sub> doped with Ce<sup>3+</sup> → (Tb<sup>3+</sup>)<sub><i>n</i></sub> →
Eu<sup>3+</sup> or (Tb<sup>3+</sup>)<sub><i>n</i></sub> →
Eu<sup>3+</sup> are synthesized to prove the universality of S →
(Tb<sup>3+</sup>)<sub><i>n</i></sub> → A in inorganic
hosts and to study the unsolved issues. Saturation distance of Tb<sup>3+</sup>–Eu<sup>3+</sup>, estimated with the empirical data
of different hosts, is proposed to be a criterion for determining
whether a spectral chromaticity coordinate keeps constant. A branch
model is put forward to replace the chain model to explain the role
of (Tb<sup>3+</sup>)<sub><i>n</i></sub> in ET from Ce<sup>3+</sup> to Eu<sup>3+</sup> and the necessity of high content of
Tb<sup>3+</sup>; the term “terbium bridge” is used to
replace “terbium chain”, and the value of <i>n</i> is determined to be two or three. The intensity quenching of Eu<sup>3+</sup> emission is attributed to the surface defects ascribed to
the smaller particles and larger specific surface area rather than
the concentration quenching of Tb<sup>3+</sup>. Based on the saturation
distance and the mechanism of luminescence quenching, the necessary
concentration of Tb<sup>3+</sup> for (Tb<sup>3+</sup>)<sub><i>n</i></sub> can be estimated as long as the cell parameters
are already known and the luminescent efficiency of Eu<sup>3+</sup> can be further improved by optimizing the synthesis method to decrease
the quantity of surface defects