The linear polarization, of a hot luminescence which comprised the resonant secondary radiation of F centers, was measured by means of time-resolved ps spectroscopy over the entire Stokes wave-number range. The linear polarization maintained a constant value of about 40% up to the onset of ordinary luminescence. It then decreased to vanishingly small values with decreasing wave-number. This implied that the optically excited F center relaxed along the 2p-like adiabatic potential energy surface trough, and transferred to the 2s-like adiabatic potential energy surface trough to form the relaxed excited state. The lattice relaxation time and the dynamic transition time were estimated to be less than 15ps.

N.Akiyama, F.Nakahara, H.Ohkura: Radiation Effects and Defects in Solids, 1995, 134, 345-8