Polarized Infrared Absorption of Dipole Centers in Cadmium Halide and PbI_2 Crystals (Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties)

概要

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Polarized infrared (IR) absorption measurements on CN^- or OH^- centers in cadmium halide and PbI_2 crystals were carried out at 6 K with a high spectral resolution of 0.025cm^<-1> at 2000cm^<-1> by using a FTIR spectrometer. Several sharp absorption lines with widths less than O.1cm^<-1> are observed in the energy region of the stretching vibration, i.e. 2000 to 2250cm^<-1> for CN^<-1> and 2500 to 4500cm^<-1> for OH^-. These lines are classified into several groups attributed to (1) an isolated center simply substituted for a halogen ion, (2) an interstitial center located between the cadmium and halogen ion sheets and (3) a coupled center with an anion vacancy or a host metal ion. Almost all of the dipole axes (bond axes) of the CN^- ions doped in MI_2 (M = Cd or Pb) are parallel to the crystal c-axes, while those of the isolated and coupled CN^- centers in CdX_2 (X = Cl or Br) lean away from the direction of the c-axis. The most OH^- ions doped in CdX_2 (X = Cl, Br or I) and PbI_2 are arranged in the halogen-ion planes with their dipole axes parallel to the crystal c-axes. The first overtone yields values of χ_e and ω_eχe for CN^- and OH^-" in CdX_2 and PbI_2. These values explain well the isotope shift of the main stretching band in CdX_2 and PbI_2.
社団法人日本物理学会の論文
2004-03-15