Mechanisms of Energy Transfer Involving Trivalent Tb and Nd in Sodium Rare-Earth Tungstates

Self-quenching of Nd emission from Nd4F3/2 in the Na0.5(Y, Nd)0.5WO4 tungstates (scheelite structure) and transfer from Nd4F3/2 to Tb or Eu involves dipole—dipole interactions. Self-quenching of Nd is largely by thermally activated interactions at 295°K. However, processes requiring the simultaneous transfer of ∼600 cm−1 to the phonon spectrum are indicated for reduced temperatures. Radiative transfer between Nd ions and excitation migration between exchange coupled Tb ions to Nd sinks are observed also. Transfer from Tb to Nd from either Tb5D3 or Tb5D4 is by dipole—quadrupole interactions. Corrections for self-quenching, internal conversion, and excessive drain time to the excited level of interest are discussed.