Study of Energy Transfer from Sb3+, Bi3+, Ce3+ to Sm3+, Eu3+, Tb3+, Dy3+

Energy transfer from the sensitizers (S) Sb3+, Bi3+, or Ce3+ to the activators (A) Sm3+, Eu3+, Tb3+, or Dy3+ has been studied in four different host lattices, viz., YOCl, YBO3, YAl3B4O12, and YPO4. The efficiency of the energy transfer in these systems varies markedly. This is the case even for a given combination of S and A in different host lattices. In most, but not all, cases SS energy transfer is also important. The SA energy transfer is probably nonradiative and occurs mainly by exchange interaction if the S emission band overlaps only 4f−4f absorption bands of A, but by electric multipole—multipole interaction, if the S emission band overlaps allowed absorption bands of A. Taking these ideas and the energy overlap of S emission and S absorption or S emission and A absorption into account, it is possible to explain the results in a qualitative way. If, however, the energy difference between the state S* (excited) +A and the state consisting of the ions S++A− is relatively small, no energy transfer by exchange is observed.