Energy transfer from linear stacks of tetracyanoplatinates(II) to rare earth ions

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Abstract
M2[Pt(CN)4]3⋅nH2O compounds (with M3+=Sm3+, Eu3+, Tb3+,...) represent a new solid state class for investigations of nonradiative excitation energy transfer. The donors are linear stacks (columns) of square planar [Pt(CN)4]2− complexes and the acceptors are rare earth ions which are located between the stacks. Radiationless energy transfer and sharp line rare earth ion emission have been observed for Sm2[Pt(CN)4]3⋅18H2O (SmCP) and Eu2[Pt(CN)]3⋅18H2O (EuCP) but not for Tb2[Pt(CN)4]3⋅21H2O (TbCP), although Tb3+ generally is a bright emitter. The results are discussed in the scope of the Förster–Dexter theory of resonance energy transfer. It is seen that the spectral overlap integral vanishes for TbCP but not for SmCP nor EuCP. The energy transfer only (or predominantly) occurs from the lower excited state of tetracyanoplatinate stacks. Using emission lifetime data, a transfer rate of 108–109 sec−1 is obtained as a lower limit. Such a high rate can only be explained, as an estimate shows, by an exchange transfer mechanism. The spectroscopic properties of the tetracyanoplatinates(II) with and without acceptor ions in the neighborhood are compared.