Optical Properties of Electron Trapped Center in Layered Ionic Crystals (CH₃NH₃)₂CdCl₄and (C₂H₅NH₃)₂CdCl₄Irradiated with X-Rays at 15 K

Abstract

New optical absorption bands (IR bands) were found at around 10∼20 kcm -1 besides absorption band of Cl 2 - molecular center in two-dimensional crystals of (CH 3 NH 3 ) 2 CdCl 4 and (C 2 H 5 NH 3 ) 2 CdCl 4 irradiated with X-rays at 15 K. The absorption intensities increase with the X-ray dosage in proportion to that of the Cl 2 - center and decrease at temperatures higher than 25 K for (CH 3 NH 3 ) 2 CdCl 4 and 35 K for (C 2 H 5 NH 3 ) 2 CdCl 4 accompanying the decrease of Cl 2 - . The both bands are also bleached by the light irradiation on the IR bands at 15 K. The IR bands are assigned to an electron center where an electron is trapped by an alkylammonium head in the neighborhood of a Cl - vacancy.