Abstract
Native point defects in ZnO are so complicated that most of them are still debating issues, although they have been studied for decades. In this paper, we experimentally reveal two sub-components usually hidden in the low energy tail of the main broad green luminescence band peaking at 547 nm (~2.267 eV) in intentionally undoped ZnO single crystal by selecting the below-band-gap (BBG) optical excitations (e.g. light wavelengths of 385 nm and 450 nm). Moreover, both sub-components are manifested as long persistent phosphorescence once the BBG excitations are removed. With the aid of a newly developed model, the energy depths of two electron traps involved within the long lived orange luminescence are determined to be 44 meV and 300 meV, respectively. The candidates of these two electron traps are argued to be most likely hydrogen and zinc interstitials in ZnO.
Highlights
Zinc oxide (ZnO) is a simple but outstanding inorganic compound having many applications in different fields such as catalysis, electro-acoustic transducers, transparent conductors, optoelectronics, paints & rubber, and pharmaceuticals etc.[1]
The overall PL spectrum consists of a sharp UV peak and a broad green luminescence (GL) band centered at ~547 nm, which is well consistent with those commonly reported for high-quality ZnO in the literature
The visible emission excited by the 385 nm light was an orange luminescence (OL) band peaking at ~607 nm, while the orange and a highly structured red luminescence (RL) bands are simultaneously observed under the excitation of 450 nm light
Summary
Zinc oxide (ZnO) is a simple but outstanding inorganic compound having many applications in different fields such as catalysis, electro-acoustic transducers, transparent conductors, optoelectronics, paints & rubber, and pharmaceuticals etc.[1]. The discovery and modeling of visible phosphorescence in high-quality ZnO single crystal under the below-band-gap (BBG) optical excitations may pave a new way to investigate the defects in ZnO19,23. We unveil the hidden orange and red sub-components of the common green luminescence (GL) band in an intentionally undoped ZnO single crystal grown with the melt-growth technique by taking BBG optical excitations.
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