Dynamics of the Optical Excitation—Deexcitation Cycle of O2− Centers in KCl

The time dependence of the fluorescence of O−2 centers following picosecond‐pulse excitation is studied. The risetime of the spontaneous fluorescence yields an upper bound for the relaxation time in the excited state: τ*R < 20 ps. The fluorescence decay time decreases from 92 ns at 4.2 K to 50 ns at 300 K. By comparing the results to superfluorescence experiments a lower bound for the relaxation time in the ground state is obtained: τR ⪆ 50 ps.