TUNABLE RADIATIONLESS ENERGY-TRANSFER IN EU[AU(CN)(2)](3)CENTER-DOT-3H(2)O BY HIGH-PRESSURE

The title compound consists of two-dimensional layers of [Au(CN)(2)](- ) complexes alternating with layers of Eu3+ ions. Due to this structur e type, the lowest electronic transitions of the dicyanoaurates(I) exh ibit an extreme red shift of Delta<(nu)over bar/Delta p = -130 +/- 10 cm(-1)/kbar under high-pressure application at least up to approximate to 60 kbar (T = 20 K), while the shifts of the different Eu3+ transit ions 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 Eu3+ accepters. A s a consequence, one observes a strong emission from Eu3+, which is as signed to stem mainly from D-5(0) but also weakly from D-5(1). At T = 20 K, D-5(3) seems to be the dominant acceptor term. It is a highlight of this investigation that, with increasing pressure, the emission fr om the dicyanoaurate(I) donor states can continuously be tuned in by t uning off the resonance condition (spectral overlap) for radiationless energy transfer to D-5(3). With further increase of pressure, success ively, D-5(2) and D-5(1) become acceptor terms, however, being less ef ficient. Interestingly, D-5(0) does not act as an acceptor term even w ith maximum spectral overlap. Between 30 and 60 kbar, when only the F- 7(0) --> D-5(1) acceptor absorption overlaps with the donor emission, one finds a linear dependence of the (integrated) D-5(0) emission inte nsity on the spectral overlap integral, as is expected for resonance e nergy transfer. As the dominant transfer mechanism, the Dexter exchang e mechanism is proposed. Besides the high-pressure studies of the Eu3 line structure at T = 20 Kt the Eu3+ 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.