  Donors in silicon hold considerable promise for emerging quantum
technologies, due to the their uniquely long electron spin coherence times. Bi
donors in silicon differ from P and other Group V donors in several significant
respects: they have the strongest binding energy (70.98 meV), a large nuclear
spin (I = 9/2) and strong hyperfine coupling constant (A = 1475.4 MHz). These
larger energy scales allow a detailed test of theoretical models describing the
spectral diffusion mechanism that is known to govern the electron spin
coherence time (T2e) of P-donors in natural silicon. We report the electron
nuclear double resonance spectra of the Bi donor, across the range 200 MHz to
1.4 GHz, and confirm that coherence transfer is possible between electron and
nuclear spin degrees of freedom at these higher frequencies.
