Electronic band structure and optical absorption of nanotubular zinc oxide doped with Iron, Cobalt, or Copper

The absorption spectra of the precursor-derived solid solutions Zn$_{1-x}$M$_x$O (M = Fe, Co, Cu) with a tubular morphology of aggregates have been investigated in the ultraviolet and visible regions. The maximum metal concentration $x$ in the Zn$_{1-x}$M$_x$O solid solutions is 0.075 for iron, 0.2 for cobalt, and 0.1 for copper. It has been found that the optical absorption and the band gap of the Zn$_{1-x}$M$_x$O compounds depend on the type of dopant. The obtained experimental data have been interpreted using the results of the performed ab initio calculations of the electronic band structure and optical absorption.