ENERGY-TRANSFER AND PICOSECOND RELAXATION OF F-CENTERS IN RBCL, KCL, AND KBR

Possible decay mechanisms of excited F centers are investigated in both additively colored and x-irradiated RbCl, KCl, and KBr, containing typically more than 3×1016 cm-3 F centers and sizable amounts of dimer (F2) and higher F aggregates. Time-resolved ground-state recovery measurements under F-band excitation at low temperature and optical-absorption data show a picosecond deexcitation process, occurring for a substantial number of F centers and possessing shorter decay times for higher relative concentrations of F2 and N centers. This establishes energy transfer from excited F to F2 centers, a controversial topic throughout the literature, and towards N centers in KCl to be both competitive relaxation channels. Transient absorption measurements in heavily colored KCl by Gadonas et al., which show increased transparency in the F2-band region 500 ps after pulsed F excitation, fully support the above conclusion. A similar behavior was also observed in RbCl and KBr. This additional decay channel could adversely affect laser operation in several color-center lasers. © 1990 The American Physical Society.