External heavy atom effect on radiative spin-forbidden transitions

Interpretation of europium(III) spectra

“…The energy levels of the Gd 3+ ion are well above those of the triplet level so that no gadolinium(III)-centered emission is observed. Moreover, the heavy paramagnetic Gd 3+ ion enhances the intersystem crossing from the singlet to the triplet state, because of mixing of the triplet and singlet states ("heavy atom effect" and "paramagnetic effect") [352][353][354][355][356]. The triplet state acquires partially a singlet character by the spin-orbit coupling interaction, and the selection rules are relaxed.…”

Fluorescent dyes as efficient photosensitizers for near-infrared Nd3+ emission

“…The reduction of the fluorescence intensity of the dye in the complex is most probably caused by an external heavy atom effect induced by the presence of the heavy and paramagnetic Nd 3ϩ ion. Due to spin-orbit coupling and paramagnetic interactions, the spin-forbidden singlet-triplet intersystem crossing process is enhanced, 15, 16 and this results in a reduction of the fluorescence intensity. The alternative processes that may deactivate the antenna singlet excited state in the presence of the lanthanide ion are singlet energy transfer and photo-induced electron transfer, but they can be ruled out.…”

“…5,15 This phenomenon is generally referred to as the external heavy atom effect. 16 The presence of the heavy and paramagnetic lanthanide ion increases the spin-forbidden intersystem crossing process of the antenna chromophore at the expense of the antenna fluorescence.…”

Synthesis of 2,6‐Bis(oxazolyl)pyridine Ligands for Luminescent LnIII Complexes

“…[10] The emission spectra exhibit the characteristic peaks for each metal ion, 5 D 0 Ǟ 7 F J (J = 0, 1, 2, 3, 4) for Eu III (578, 592, 614, 652, and 698 nm) and 5 D 4 Ǟ 7 F J (J = 6, 5, 4, 3, 2, 1) for Tb III (489, 545, 583, 620, 652, and 668 nm) ( Figure 2). [10] The emission spectra exhibit the characteristic peaks for each metal ion, 5 D 0 Ǟ 7 F J (J = 0, 1, 2, 3, 4) for Eu III (578, 592, 614, 652, and 698 nm) and 5 D 4 Ǟ 7 F J (J = 6, 5, 4, 3, 2, 1) for Tb III (489, 545, 583, 620, 652, and 668 nm) ( Figure 2).…”

“…The shapes of the absorption and excitation spectra are virtually identical for the complexes of both metals, which is consistent with sensitization of the lanthanide emission 2,6-Bis(oxazolyl)pyridine Ligands for Luminescent Ln III Complexes through absorption of light by the ligand and subsequent energy transfer to the lanthanide ion, in general occurring by an electron-exchange mechanism. [10] The emission spectra exhibit the characteristic peaks for each metal ion, 5 D 0 Ǟ 7 F J (J = 0, 1, 2, 3, 4) for Eu III (578, 592, 614, 652, and 698 nm) and 5 D 4 Ǟ 7 F J (J = 6, 5, 4, 3, 2, 1) for Tb III (489, 545, 583, 620, 652, and 668 nm) ( Figure 2).…”