Tunable Energy Transfer from Dicyanoaurate(I) and Dicyanoargentate(I) Donor Ions to Terbium(III) Acceptor Ions in Pure Crystals

A temperature-dependent photoluminescence study is reported for single crystals of M[Au(CN) 2 ] 3 and M[Ag(CN) 2 ] 3 (M = Tb; Gd; Y). The results indicate that in both Tb[Au(CN) 2 ] 3 and Tb[Ag(CN) 2 ] 3 exclusive excitation of the donor leads to sensitized luminescence for the acceptor, characteristic of the 5 D 4 → 7 F J ( J = 0−6) transition of Tb(III). However, the sensitized luminescence is much stronger in Tb[Ag(CN) 2 ] 3 than in Tb[Au(CN) 2 ] 3 due to a larger spectral overlap between the [Ag(CN) 2 - ] emission and the Tb(III) absorption. Upon increasing the temperature, energy transfer is enhanced in Tb[Ag(CN) 2 ] 3 but inhibited in Tb[Au(CN) 2 ] 3 . In Tb[Ag(CN) 2 ] 3, a large spectral overlap exists between the [Ag(CN) 2 - ] donor emission and the Tb(III) acceptor absorption at all temperatures. The Tb(III) sensitized emission is strong at all temperatures and is enhanced upon a temperature increase while the [Ag(CN) 2 - ] emission is quenched. An activation energy of 53.7 cm - 1 (±2.5 cm - 1 ) has been calculated for the energy transfer process in Tb[Ag(CN) 2 ] 3 . In Tb[Au(CN) 2 ] 3, the Tb(III) sensitized luminescence decreases upon increasing the temperature. The [Au(CN) 2 - ] emission is strong and does not undergo a complete quenching as the temperature increases toward room temperature. The [Au(CN) 2 - ] emission undergoes a red shift upon cooling, which leads to an increased spectral overlap with the 5 D 4 → 7 F 6 absorption band of Tb(III); thus energy transfer is tuned by controlling the temperature. The sensitized luminescence intensity of Tb(III) in Tb[Au(CN) 2 ] 3 is directly proportional to the numerical value of the donor−acceptor spectral overlap, in agreement with the theory of radiationless energy transfer.