Thiocyanates as novel host lattices for emitting rare earth ions:: Luminescence of Sr(SCN)2:Eu2+

Excitation and emission spectra of Sr(SCN)(2):Eu2+ at different temperatures are presented. A strong bright green emission due to 4f(6)5d(1) --> 4f(7) transitions is observed at low temperature. The spectra of this new kind of host lattices are compared to those of sulfides and nitrides. This comparison shows that the influence of the degree of covalency of the host lattice is remarkably large. Additionally, some Fano antiresonances due to S-8 --> 6I(j) and S-8 --> D-6(J) transitions are observed in the excitation spectra. The luminescence is strongly quenched with increasing temperatures, and no emission could be observed above 220 K. The lifetime is 453 ns at 12 K. Due to the shape of the excitation spectra, the quenching behavior with increasing temperature, and the short lifetimes, it can be assumed that there is an increasing amount of nonradiative relaxation at higher temperature. These observations are explained by the fact that the excited 4f(6)5d(1) state is located in the vicinity of the conduction band and the respective excitonic state is thermally populated followed by nonradiative relaxation to the ground state.