TRANSFORMATION OF PHONON MODE BEHAVIOR IN THE AGCLXBR1-X SYSTEM

Systematic studies of far infrared reflection spectra and photoluminescence spectra of free excitons have been performed in AgClxBr1-x mixed crystals at low temperatures in the composition range x = 0 to 1 and between x = 0.10 and 0.39, respectively. Reflection spectra exhibit the existence of two TO-phonon modes for 0.03 less-than-or-equal-to x less-than-or-equal-to 0.50, whereas only one TO-phonon mode is recognized for x > 0.87. Variation of reflection bands with the composition x indicates the transformation of phonon mode behaviour from the two-mode type to the one-mode type with increasing x. Photoluminescence spectra also exhibit the existence of two LO-phonon modes in AgBr-rich crystals, 0.12 less-than-or-equal-to x less-than-or-equal-to 0.27.