Time-resolved transient spectral hole-burning experiments in zero field and in low magnetic fields B( parallelc) are reported for the chromium(III) R(1)-line, 2A((2)E)<-- 2A((4)A(2)) of Chatham lab created emerald, Be(3)Al(2)Si(6)O(18)ratio Cr(III)(0.0017% per weight), in the temperature range of 3 to 12 K. In low magnetic fields and temperatures >5 K conversion of side-holes to anti-holes is observed with progressing time. Anti-holes are due to the population stored in ground state levels. The dynamics of the hole pattern can be well modelled by a set of coupled differential equations for the levels of the (4)A(2) and (2)E multiplets. The measurements allow the simultaneous determination of g-factors and spin-lattice relaxation rates in the excited state and the ground state. At 6 K the relaxation times between the split +/-1/2 2A((2)E) excited state levels and +/-3/2 2A((4)A(2)) levels of the ground state are about 0.16 ms and 9 ms, respectively. From the temperature dependence it follows that the spin-lattice relaxation rates are dominated by Orbach processes in the experimental temperature range.
Photon-gated hole burning, or selective bleaching enabled by a second light source, has been observed in
Co2+ in tetrahedral sites of
LiGa5O8. This leads to long-lived spectral holes with a width of \ensuremath{\sim}1 GHz at 1.6 K. It is proposed that two-step photoionization of
Co2+ is responsible for the hole burning. Much narrower (\ensuremath{\sim}40 MHz) transient holes and antiholes were burned using population storage in nuclear hyperfine levels. These two mechanisms of hole burning are reported here for transition-metal ions for what is believed to be the first time.