CLUSTERING PROCESSES IN CAF2-GD-GD+SM(LU AND CAF2)

The combined results obtained by ionic thermal currents OTC) and elect ron paramagnetic resonance (EPR) techniques on CaF2 double-doped eithe r with Gd+Lu or Gd+Sm are presented here. Tn both systems a fraction o f the Gd ions are observed in tetragonal and cubic sites. The Gd+Lu sy stems shows a very weak ITC spectrum in contrast to the Gd+Sm samples which present at least eight peaks of dipolar origin. The differences observed are accounted for by the existence in one case of an hexamer structure from the lowest Lu doping level and in the second case by th e scavenging of F-i(-) by clusters of increasing size with the Sm conc entration. The experimental results confirm the predictions from HADES simulations that take into account the ion size effects.