Tunable Radiationless Energy Transfer in Eu[Au(CN) 2 ] 3 ·3H 2 O by High Pressure

The title compound consists of two-dimensional layers of [Au(CN) 2 ] - complexes alternating with layers of Eu 3+ ions. Due to this structure type, the lowest electronic transitions of the dicyanoaurates(I) exhibit an extreme red shift of Δν̄ max /Δ p = −130 ± 10 cm - 1 /kbar under high-pressure application at least up to ≈60 kbar ( T = 20 K), while the shifts of the different Eu 3+ transitions lie between −0.70 and −0.94 cm - 1 /kbar. At ambient pressure, the usually very intense emission of the dicyanoaurates(I) is completely quenched due to radiationless energy transfer to the Eu 3+ acceptors. As a consequence, one observes a strong emission from Eu 3+, which is assigned to stem mainly from 5 D 0 but also weakly from 5 D 1 . At T = 20 K, 5 D 3 seems to be the dominant acceptor term. It is a highlight of this investigation that, with increasing pressure, the emission from the dicyanoaurate(I) donor states can continuously be tuned in by tuning off the resonance condition (spectral overlap) for radiationless energy transfer to 5 D 3 . With further increase of pressure, successively, 5 D 2 and 5 D 1 become acceptor terms, however, being less efficient. Interestingly, 5 D 0 does not act as an acceptor term even with maximum spectral overlap. Between 30 and 60 kbar, when only the 7 F 0 → 5 D 1 acceptor absorption overlaps with the donor emission, one finds a linear dependence of the (integrated) 5 D 0 emission intensity on the spectral overlap integral, as is expected for resonance energy transfer. As the dominant transfer mechanism, the Dexter exchange mechanism is proposed. Besides the high-pressure studies of the Eu 3+ line structure at T = 20 K, the Eu 3+ emission is also investigated at T = 1.2 K ( p = 0 kbar) by time-resolved emission spectroscopy, which strongly facilitates the assignments of the emitting terms.