Spectroscopic studies of polaron and bipolaron defects in the stringly localized CDW solid [Pt II(en) 2][Pt IV(en) 2Cl 2](CIO 4) 4

Abstract

The resonance Raman spectroscopy of defect states in [Pt(en) 2][Pt(en) 2Cl 2](CIO 2) 4 serves to resolve the twwo intragap defect adsorption features (A and B bands) located immediately to the red of the charge transfer band edge into five separate transition. Of these five absorptions, two are associated with a mode at 263 cm −1, assigned to electron polarons, and two with a mode at 287 cm −1, assigned to hole polarons, while a fifth band, associated with a mode at 272 cm −1, is not readily assigned. Of the polaron absorptions, we find that the electron and hole defects exhibit offset adsorptions in the order Ap − <Ap + < Bp +t < Bp +, where P − and P + refer to electron and hole polarons, respectively. This energy asymmetry can be quantitatively reproduced by a two band 3/4-filled model that includes both the metal and halides bands. Alternatively, the asymmetry may be a result of preferential pinning of one type of polaron at a preexisting defect site on the lattice. Temperature dependence of the defect Raman signals shows that the 287 cm −1 hole polaron and the unassigned 272 cm −1 peaks are diminished by raising temperature from 12 to 200 K while the 263 cm −1 electron polaron signal gains relative intensity over this temperature range.