抄録
A color center, denoted as the P.F center, has been found in KCl crystals doped with alkaline earth or rare earth ions, as an intermediate product in the stage of optical F→FZ conversion. The P.F center is characterized by absorption and emission spectra closely resembling to those of F centers, but much shorter fluorescence decay-time, 230 ns, as compared with the F center. It is proposed that the P.F center is an F center perturbed by the electric field of an impurity-complex. Using the data on the P.F center, the lifetime of the 2p→1s transition for the unperturbed F center is determined as 50 ns, on the basis of the vibronic model proposed by Ham and Grevsmühl. The experimental data on F centers can be explained consistently only when the energy difference between the 2s and 2p states are assumed to be about 0.05 eV. The result also suggests that the relaxed excited state of the F center is more contracted than predicted by Fowler’s large orbit hypothesis.
