(INVITED) Energy transfer processes in Sr3Tb(PO4)3 eulytite-type materials singly doped with Nd3+ and Sm3+

In this study the optical spectroscopy, the excited state dynamics and in particular the energy transfer Tb3+→Ln3+ (Ln = Nd or Sm), have been investigated in detail in eulytite double phosphate hosts of the type Sr3Tb(PO4)3 doped with 1 mol% Ln3+. It has been found that for Ln=Nd and Sm, the energy transfer efficiency (ηT) is 0.76 and 0.73, respectively, thanks to the assistance of fast migration in the Tb3+ 5D4 level. The pathway responsible for the transfer of excitation has been unambiguously identified in the case of Sr3Tb0.99Nd0.01(PO4)3, whilst the situation is more complex for Sr3Tb0.99Sm0.01(PO4)3, due to high density of the final Sm3+ states that could be involved. The Tb3+→Nd3+ energy transfer has been tentatively attributed to the exchange interaction on the basis of the short transfer distance and multipolar selection rules.