Enhanced Lasing Properties of Dissymmetric Eu(III) Complex with Bidentate Phosphine Ligands

The luminescent and lasing properties of Eu(III) complexes were enhanced by using an dissymmetric Eu(III)
complex. The photophysical properties (the emission spectral shapes, the emission lifetimes, the emission
quantum yields, and the stimulated emission cross section (SEC)) were found to be dependent on the geometrical
structures of Eu(III) complexes. The geometrical structures of Eu(III) complexes were determined by X-ray
single crystal analyses. The symmetrical group of Eu(hfa)3(BIPHEPO) (tris(hexafluoroacetylacetonato)europium(III) 1,1‘-biphenyl-2,2‘-diylbis(diphenylphosphine oxide)) was found to be C1, which was more
dissymmetric than Eu(hfa)3(TPPO)2 (tris(hexafluoroacetylacetonato)europium(III) 1,2-phenylenebis(diphenylphosphine oxide):  C2 symmetry) and Eu(hfa)3(OPPO)2 (tris(hexafluoroacetylacetonato)europium(III) 1,2-phenylenebis(diphenylphosphine oxide):  C2 symmetry). The analytical data were supported by Judd−Ofelt
analysis. The most dissymmetrical Eu(III) complex, Eu(hfa)3(BIPHEPO), showed large electron transition
probability and large SEC (4.64 × 10-20 cm2). The SEC of Eu(hfa)3(BIPHEPO) was superior to even the
values of Nd-glass laser for practical use (1.6−4.5 × 10-20 cm2). The lasing properties of Eu(III) complexes
in polymer thin film were measured by photopumping of a Nd:YAG laser (355 nm). The threshold energy of
lasing oscillation was found to be 0.05 mJ. The increasing rate of the lasing intensity of Eu(hfa)3(BIPHEPO)
as a function of the excitation energy was much larger than that of Eu(hfa)3(TPPO)2 and Eu(hfa)3(OPPO)2.
The dissymmetrical structure of Eu(hfa)3(BIPHEPO) promoted the enhancement of the lasing property.