Self-trapping of the d-d charge transfer exciton in bulk NiO evidenced by X-ray excited luminescence
V. I. Sokolov, V. A. Pustovarov+, V. N. Churmanov+, V. Yu. Ivanov+, N. B. Gruzdev, P. S. Sokolov*, A. N. Baranov*, A. S. Moskvin×
Institute of Metal Physics UD RAS, 620990 Ekaterinburg, Russia
+Ural Federal University, 620002 Ekaterinburg, Russia
*Lomonosov Moscow State University, 119991 Moscow, Russia
×Department of Theoretical Physics, Institute of Natural Science, Ural Federal University, 620083 Ekaterinburg, Russia
Abstract
Soft X-ray (XUV) excitation did make it possible to avoid the
predominant role of the surface effects in luminescence of NiO and revealed a
bulk luminescence with a puzzling well isolated doublet of very narrow lines
with close energies near 3.3 eV which is assigned to recombination
transitions in self-trapped d-d charge transfer (CT) excitons formed by
coupled Jahn-Teller Ni+ and Ni3+ centers. The conclusion is
supported both by a comparative analysis of the CT luminescence spectra for
NiO and solid solutions NixZn1-xO, and by a comprehensive cluster
model assignement of different p-d and d-d CT transitions, their
relaxation channels. To the best of our knowledge, it is the first observation
of the luminescence due to self-trapped d-d CT excitons.