ALLOYING EFFECT ON THE N=1 AND N=2 EXCITONS IN MIXED K1-XRBXI CRYSTALS

Alloying effect on the exciton reflection spectra has been studied for mixed K1-xRbxI single crystals (0 less than or equal to x less than o r equal to 1) at 10 K. The shoulder like structure of the n = 1 excito n band, which arises from the exciton-phonon interaction, is kept well over the whole concentration range. On the other hand. the multiple L O-phonon sidebands of the n = 2 exciton are smeared out upon alloying, These results reveal that the alloying effect is very sensitive to th e spatial extension of excitons. Furthermore, free-exciton luminescenc e is observable even in the intermediate region of x, indicating that the exciton is not localized by the potential fluctuations in K1-xRbxI crystals.