Optical properties of quasi-one-dimensional MMX-chain compounds: R4[Pt2(pop)4X].nH2O, (R=K and NH4, X=Cl and Br)

Polarized reflection and luminescence spectra of single crystals of quasi-one-dimensional halogen bridged binuclear metal complexes (MMX-compounds), R4[Pt2(pop)4X].nH2O (R=K and NH4; X=Cl and Br; n=0 (R=NH4) and 3 (R=K); pop=P2O5H22−) have been measured. Intense asymmetric Lorenzian-like absorption bands caused by charge transfer excitons from Pt2+Pt2+ ions to the neighboring Pt3+Pt3+ ions polarized parallel to the chain axis have been observed. A board luminescence band with large Stokes sift energy caused by the radiative recombination of the self-trapped excitons has been observed. These features are the characteristics features of the charge density wave systems. In K4[Pt2(pop)4Cl].3H2O, coexistence of two CT-absorption bands have been observed.