Electron spin dynamics in Ce3+ : YAG crystals: Hyperfine interaction of 4f and 5d electrons

The electron spin dynamics of $\mathrm{C}{\mathrm{e}}³⁺$ ions in YAG crystals is studied by time-resolved photoluminescence spectroscopy with an alternating left and right circularly polarized continuous-wave laser modulation technique. The electron spin relaxation due to hyperfine interaction with randomly oriented nuclear spins can be efficiently suppressed by a weak external longitudinal magnetic field. The suppression of the hyperfine-induced spin relaxation makes the electron spin polarization increase from 0.001 to 0.016 for the lowest $4f$ state, and from 0.08 to 0.32 for the lowest $5d$ state. The suppression magnetic fields for the $4f$ electrons are several times weaker than that for the $5d$ electrons, dependent on the crystal orientation. The dispersion of the local hyperfine field distribution $\mathrm{\ensuremath{\Delta}}B$ is isotropic and equal to 4.0 mT for the $5d$ electrons, and anisotropic for the $4f$ electrons with $\mathrm{\ensuremath{\Delta}}{B}_[001]=0.8\phantom{\rule{0.16em}{0ex}}\mathrm{mT},\mathrm{\ensuremath{\Delta}}{B}_[110]=1.1\phantom{\rule{0.16em}{0ex}}\mathrm{mT},\mathrm{\ensuremath{\Delta}}{B}_{[1\overline{1}0]}=2.4\phantom{\rule{0.16em}{0ex}}\mathrm{mT}$. The hyperfine coupling strength for the $4f$ electrons is \ensuremath{\sim}4 times weaker than that for the $5d$ electrons.