Luminescent Properties of Co-Doped Complexes of Eu(III)- Tb(III) with 2,4,6-Pyridinetricarboxylate

   A series of Eu(III)-Tb(III) co‑doped complexes was synthesized under hydrothermal conditions at 180 °C by reacting europium(III) and terbium(III) perchlorates with 2,4,6‑pyridinetricarboxylic acid (ptc) in systematically varied molar ratios. The molar ratios of Eu(III) to Tb(III) employed during synthesis were as follows: 1.0:0 (1), 0.9:0.1 (2), 0.8:0.2 (3), 0.7:0.3 (4), 0.6:0.4 (5), 0.5:0.5 (6), 0.4:0.6 (7), 0.3:0.7 (8), 0,2:0.8 (9), 0.1:0.9 (10), and 0:1.0 (11). The excitation and emission spectra, luminescence lifetimes, and quantum yields of the complexes were measured. Emission spectroscopy analysis revealed that under ultraviolet excitation, the luminescent color of the complexes gradually shifted from red to orange, yellow, and green as the Eu(III) content decreased and the Tb(III) content increased. Luminescence lifetime measurements showed that the pure Eu(III) complex (1) exhibited the shortest lifetime. In the co-doped complexes, the lifetime of the Eu(III) ⁵D0→⁷F₂ transition gradually increased as the Eu(III) content decreased. Conversely, the pure Tb(III) complex (11) displayed the longest lifetime, and the lifetime of the Tb(III) ⁵D4→⁷F₅ transition decreased rapidly as the Tb(III) content was reduced. Absolute quantum yield (QY) measurements indicated that the pure Eu(III) complex (1) had the lowest QY, whereas the pure Tb(III) complex (11) showed the highest. Among the co-doped complexes (2–10), the QY gradually increased with decreasing Eu(III) content, and correspondingly decreased with increasing Eu(III) content. These results suggest that in this series of complexes, Tb(III) can sensitize the luminescence of Eu(III), whereas Eu(III) exerts a quenching effect on the luminescence of Tb(III).

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