Femtosecond spectroscopy for the dynamics of relaxation of excitons in solids with strong electron-phonon coupling

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Lattice relaxation of excitons in alkali halides, fluorites, and SiO_2 have been studies by means of time-resolved spectroscopy in femtosecond time regime. Our new findings and results obtained in this study are summarized as follows :(1)Initial formation yields of F-H pairs and triplet self-trapped excitons, STEs, in alkali halides show a clear complementary relation.(2)Optical transition energies of self-trapped holes in amorphous SiO_2 have been determined.(3)Luminescence from the singlet STE in SiO_2 have been identified for the first time.(4)Self-trapping processes of holes in KBr and KI have been resolved for the first time. In particular, holes in KI are self-trapped into the well-known V_k center via an one-center type self-trapped state.(5)Initial process of F-center formation in alkali bromides has been found to involve two different pathways ; one directly from the electron-hole pairs under relaxation and the other via the off-center instability from the on-center STEs.(6)Relaxation of electron-hole pairs in CaF_2 has been observed for the first time in femtosecond time regime. The relaxation pathways are found to be similar to those in alkali halides.