Electron spin phase relaxation of phosphorus donors in nuclear spin   enriched silicon
  We report a pulsed EPR study of the phase relaxation of electron spins bound to phosphorus donors in isotopically purified 29^Si and natural abundance Si single crystals measured at 8 K. 
Eisuke Abe, Kohei M. Itoh, Junichi Isoya, and Satoshi Yamasaki