Optical transitions and multiphonon Raman scattering of Cu doped ZnO and MgZnO ceramics

Abstract

Cu doped ZnO and MgZnO ceramics were created via a process of cold pressing and annealing, and their optical properties and phonon dynamics were studied. It was found that the ceramics exhibit infrared absorption peak energies at 5783 and 5822 cm−1, indicative of intraband transitions in a substitutional Cu ion of oxidation state +2. The UV photoluminescence (PL) intensity of the ceramics was found to weaken significantly relative to an undoped sample. The low PL intensity is discussed in terms of the CuxZn1−xO alloy system and the indirect bandgap of the CuO end member, as well as in terms of the nonradiative Cu centers. Due to the weak PL, up to ten LO multiphonons were observed in the Raman spectra, pointing to a strong polaron coupling. The resonance behavior of the highest intensity mode was found to exhibit outgoing resonance characteristics.