Optical Properties of Electron Center in Layered Ionic Crystals (C_nH_2n+1NH₃)₂MnCl₄: n=1, 2, 3 Irradiated with X-Rays at 15 K

Abstract

A new optical absorption band was found at the peak energy of 17 kcm⁻¹ (590 nm) besides the Cl₂⁻ band (22.5 kcm⁻¹=445 nm) in (C_nH_2n+1NH₃)₂MnCl₄ (n=1, 2, 3) irradiated with X-rays at 15 K. The absorption intensity of the new band increases with the X-ray dosage in proportion to that of the Cl₂⁻ band. The intensity thermally decreases in two steps at temperatures around 50 K and 80 K accompanying the decrease of Cl₂⁻ band. The absorption band can not be bleached by the 590 nm light (17 kcm⁻¹) at 15 K. The band is assigned to an electron center where an electron is trapped at the ammonium head in the neighborhood of a Cl⁻ vacancy.