Abstract
Four emission bands have been studied at low temperatures with differently doped ZnO crystals. In the () ion, two transitions to the (F) ground state give rise to new luminescence bands, viz., starting from the (F) term (around 3600 ) and from the mixed (P)(G), levels (around 15 100 ). Fine-structure and polarization properties of these transitions agree with conclusions on and spin-orbit splittings drawn from previous absorption data. An emission of ZnO:Ni near 6000 is identified as the (F)(F) transition of the () ion in a trigonal environment. While the samples display the () transmission spectrum, a charge-transfer process leads to a donor-type conversion of the center entailing the transient state. A similar mechanism is proposed to explain the emission of ZnO:Cu in the 5600–6900- range. Its fine-structure and polarization behavior can be understood in terms of (F) →(F) transitions of a () ion. Its occurrence is established in a model of one-electron configurations also covering the other known Cu transitions. The excitation spectrum presented is explained by a Tanabe-Sugano type of reasoning for the excited states which are reached in the → conversion.
- Received 5 May 1986
DOI:https://doi.org/10.1103/PhysRevB.35.18
©1987 American Physical Society