Pyridine-2,6-dicarboxylic acid for the sensitization of europium(iii) luminescence with very long lifetimes

Abstract

Convenient and mild syntheses of two europium(III) complexes, Na[Eu(dipic)₂·3H₂O]·4H₂O (dipic = dipicolinate anions) and Na[Eu(dipic)₂·phen]·H₂O (phen = 1,10-phenanthroline), were reported. These two europium(III) complexes were confirmed by ¹H NMR, FT-IR, UV-Vis spectroscopy, and elemental and lifetime analysis. Interestingly, the lifetimes were 2.31 ms and 2.38 ms for Na[Eu(dipic)₂·3H₂O]·4H₂O in the solid state and in ethanol solution, respectively, though high-frequency vibrations were present in the first coordination sphere. Furthermore, the lifetime for Na[Eu(dipic)₂·phen]·H₂O in ethanol solution is 3.23 ms, which is the longest lifetime reported to date. The Na[Eu(dipic)₂·phen]·H₂O complexes exhibited a quantum yield of 36.1% in ethanol solution, which was longer than that of Na[Eu(dipic)₂·3H₂O]·4H₂O. The value of the stimulated emission cross-section (σ_p) for Na[Eu(dipic)₂·phen]·H₂O in ethanol was very close to the values of the Nd-glass laser for practical use, which showed that it had potential application as a high-powered liquid laser medium.