Nitrogen-Ion Implantation Induced Bandgap Tailoring in Multifunctional Brownmillerite KBiFe<inf>2</inf>O<inf>5</inf>

In the present work, KBiFe2O5 (KBFO) films were implanted with 1 MeV N+-ions at different fluencies i.e., 1015, 1016 and 1017 ions cm-2 and their structural, optical and electronic properties were analyzed. From the X-ray diffraction studies, it is evident that the crystal structure of these films belong to that of brownmillerite. Effective bandgaps of these implanted films, as observed from the UV-visible absorption spectroscopy, are tuned from 1.72 eV to 1.60 eV with increasing the ion fluences. X-ray photoelectron spectroscopy reveals that the valence states of Bi and Fe ions in both pristine and implanted films are in trivalent states and also confirm the presence of nitrogen in the implanted films. A clear shift in valence band (VB) edge position towards lower binding energy in N+-ion implanted films is observed due to the occupation of N 2p states above O 2p states in the VB.