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

用飞秒时间分辨光谱研究了碱金属卤化物、萤石和SiO_2中激子的晶格弛豫。我们的新发现和结果概括如下：（1）碱金属卤化物中F-H对和三重态自陷激子（STE）的初始形成产额存在明显的互补关系。（2）测定了非晶SiO_2中自陷空穴的光学跃迁能。（3）首次发现了SiO_2中单重态STE的发光。（4）首次解决了KBr和KI中空穴的自陷过程。特别地，KI中的空穴通过单中心型自陷态自陷到众所周知的V_k中心。（5）碱金属溴化物中F心形成的初始过程涉及两条不同的途径：一条是由弛豫过程中的电子-空穴对直接形成的，另一条是由中心上的STE通过偏离中心的不稳定性形成的。（6）首次在飞秒时间范围内观察到CaF_2中电子-空穴对的弛豫。弛豫途径被发现是类似的碱金属卤化物。

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.