A Comprehensive Strategy to Boost the Quantum Yield of Luminescence of Europium Complexes

Abstract

Lanthanide luminescence has many important applications in anion sensing, protein recognition, nanosized phosphorescent devices, optoelectronic devices, immunoassays, etc. Luminescent europium complexes, in particular, act as light conversion molecular devices by absorbing ultraviolet (UV) light and by emitting light in the red visible spectral region. The quantum yield of luminescence is defined as the ratio of the number of photons emitted over the number of UV photons absorbed. The higher the quantum yield of luminescence, the higher the sensitivity of the application. Here we advance a conjecture that allows the design of europium complexes with higher values of quantum yields by simply increasing the diversity of good ligands coordinated to the lanthanide ion. Indeed, for the studied cases, the percent boost obtained on the quantum yield proved to be strong: of up to 81%, accompanied by faster radiative rate constants, since the emission becomes less forbidden.

Seven‐Coordinate Luminophores: Brilliant Luminescence of Lanthanide Complexes with C3v Geometrical Structures

“…[10][11][12][13][14][15][16][17][18][19][20][21] Lanthanide complexes with asymmetric coordination structures exhibit high emission quantum yields (Φff) and large radiative rate constants (kr). [22,23] Lanthanide complexes generally provide eightcoordinate square anti-prism structures that are categorized as D4d in point group theory (8-SAP, Figure 1a). Recently, Hasegawa and co-workers have synthesized more asymmetric lanthanide complexes with eight-coordinate trigonal dodecahedron (8-TDH: D2d, Figure 1b) and nine-coordinate monocapped square anti-prism (9-SAP: C4v, Figure 1c) structures.…”

Synthesis and Photoluminescence Properties of Nonanuclear Tb(III) Clusters with Long Alkyl Chain Group

“…The radiative rate constants k r observed for lanthanide complexes greatly depend on the geometrical symmetry of the coordination structure. Lima et al has demonstrated that the distortion of coordination geometry of lanthanide ion leads to high emission quantum yields [7]. We have also reported that the asymmetric dodecahedron structure give rise to high k r [9].…”

“…In order to maximize the luminescence efficiency of lanthanide complexes, two considerable approaches are commonly accepted [7,8]. The one is suppressing nonradiative rate constant k nr and the other is enhancing radiative rate constant k r .…”

Flexible inorganic–organic thin film phosphors by ALD/MLD

“…[1][2][3] Luminescent europium complexes act as light conversion molecular devices, and offer an attractive substituent for the commonly used organic fluorophores due to their photochemical stability, long luminescence lifetimes and sharp emission peaks. 4 The Laporte-forbidden transitions of europium causing weak excitation of electrons are overcome by using a sensitizing chromophore or antenna as a ligand in the complex. 4 Various N-heterocyclic ligands including pyridine, phenanthroline, benzimidazole, pyrazole, oxazoline, hydroxylquinoline, azaxanthone, etc., have been employed as efficient sensitizing chromophores for the photoluminescence of europium; in particular, aromatic pyridine ligands are good candidates for enhancing the luminescence properties of Eu and other lanthanides due to their strong binding abilities to the lanthanide ions.…”

“…4 The Laporte-forbidden transitions of europium causing weak excitation of electrons are overcome by using a sensitizing chromophore or antenna as a ligand in the complex. 4 Various N-heterocyclic ligands including pyridine, phenanthroline, benzimidazole, pyrazole, oxazoline, hydroxylquinoline, azaxanthone, etc., have been employed as efficient sensitizing chromophores for the photoluminescence of europium; in particular, aromatic pyridine ligands are good candidates for enhancing the luminescence properties of Eu and other lanthanides due to their strong binding abilities to the lanthanide ions. 5,6 The pyridine chromophores incorporated in chelate ligands such as beta-diketonates or carboxylate ligands are known to afford highly stable complexes which prevent the non-radiative decay.…”