Electron spin dynamics in C e3+: YAG crystals: Hyperfine interaction of 4f and 5d electrons

The electron spin dynamics of Ce3+ 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 ΔB is isotropic and equal to 4.0 mT for the 5d electrons, and anisotropic for the 4f electrons with ΔB[001]=0.8mT,ΔB[110]=1.1mT,ΔB[110]=2.4mT. The hyperfine coupling strength for the 4f electrons is ∼4 times weaker than that for the 5d electrons.