Jahn-Teller Type Self-Trapping of Holes in Mixed Crystals AgBr1-xClx

Electron spin resonance study shows that holes in Cl-rich AgBr 1- x Cl x mixed crystals are self-trapped as the Ag 2+ complexes having Br ligand ions, (AgBrCl 5 ) 4- , (AgBr 2 Cl 4 ) 4- I, II and (AgBr 4 Cl 2 ) 4- besides (AgCl 6 ) 4- . The complexes (AgBr 2 Cl 4 ) 4- II and (AgBr 4 Cl 2 ) 4- which have two and four Br ligand ions in the same plane respectively have the tetragonal symmetry due to the crystalline field created by Br ions and the Jahn-Teller effect. The anisotropy in g values for these complexes is, however, reduced somewhat compared with that expected by the static Jahn-Teller effect. The decay temperatures of the complexes (AgCl 6 ) 4- and (AgBrCl 5 ) 4- are decreased with the increase of the concentration of Br ions. This fact is discussed with the theory of optical-phonon-assisted hopping.