Cross-relaxation process between +3 rare-earth ions in LiYF4 crystals

The cross-relaxation probability (sec(-1)) involving the S-5(2) and I-5(8) levels of holmium ions in LiYF4 was investigated and its concentration dependence determined. By using a random distribution function of ions in the crystal, it was possible to determine the concentration dependence of the nonradiative probability for the ion-ion energy transfer by dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole electric interactions. The applied model shows that the ion-ion cross-relaxation transfer between Ho3+ ions in LiYF4 crystals, cannot account for the experimental results. At a high concentration level of activators (>1%), the excited ion must interact with two neighbors of same specie competing with the single ion cross-relaxation transfer.