In this communication the diffusion of neodymium into rfsputtered films of tantalum pentoxide (Ta2O5) has been investigated using the SIMS technique. The diffusion characteristics were obtained for, a temperature of 1100degreesC, and the results showed a time-dependent diffusion coefficient that reflects a transition of the sputtered films from the amorphous to the crystalline phase. The potential for doping films of Ta2O5 with neodymium by diffusion, for the realization of novel active optical devices, is also discussed.