The manifestation of excitons in low-temperature luminescence spectra of solid solutions of zinc and nickel oxides

The X-ray luminescence spectra of Zn1-xNixO solid solutions of a number of compositions, including nickel oxide (x = 1), were studied in the vicinity of I-1 and I-2 lines with energies of 3.339 and 3.393 eV. A strong temperature dependence of these lines, similar to that which occurred during observation of donor and acceptor excitons of 3d impurities in compounds II-VI:3d, as well as a change in the intensity ratio with an increase in temperature and different decay kinetics, were found earlier, which made it possible to link the origin of I-1 and I-2 lines with radiative decay of excitons of various natures. Based on the results obtained in the work, it was confirmed that the band gap width of these compounds does not depend on the composition of the solutions (i.e., on the concentration x), and a set of nickel states, both d and s types, is found in NiO near the conduction band bottom. Based on the analysis of the electron energy spectrum calculated for the studied Zn1-xNixO solid solutions, it was established that one of the observed lines of the X-ray luminescence spectrum is associated with an exciton of s-p type, and the other one-with an exciton of p-d type. Published under license by AIP Publishing.