Three photo-induced absorption bands of one-dimensional halogen-bridged mixed-valence complex, [Pt(en) 2][PtBr 2(en) 2](SO 4) 2.6H 2O

Abstract

Weak absorption bands below the low-energy absorption edge of the intervalence charge-transfer (IVCT) transition in one-dimensional halogen-bridged mixed-valence complex [Pt(en) 2][PtBr 2(en) 2](SO 4) 2.6H 2O have been investigated at 4.2K for the light polarized parallel to the Pt chain axis. In this complex, we found that three weak absorption bands (A-, B-, C-bands) were observed below the IVCT band. It is the first example of a non-doped halogen-bridged mixed-valence complex having three weak absorption bands. The absorption intensity of the C-band is much weaker than those of the A- and B-bands, but it is remarkably enhanced by the Au-doping. The A-, B- and C-bands have the photo-induced absorption effect, and its effect depends sensitively on the crystal quality and on the condition of the crystal growth, and is enhanced by the Au-doping. The photo-induced absorption decays during several minutes since stopping the irradiating light in the region of the IVCT band. From these behaviors of the A-, B-, and C-bands, we discuss the relation between the origin of these bands and the mismatch of the valence alternation.