ZnO Oxygen Vacancies Formation and Filling Followed by in Situ Photoluminescence and in Situ EPR

Abstract

Oxygen vacancies of zinc oxide were followed by photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies. The green PL emission was associated with oxygen vacancies: its intensity is enhanced upon static thermal treatment under inert or under vacuum, whereas it decreases upon oxygen treatment. A unique EPR signal at g = 1.96 was measured at room temperature after thermal in situ treatment under flow of inert or oxygenated atmospheres, its double integration follows the same trends than the green PL emission and its evolution was shown to probe the oxygen vacancy concentrations. The relative concentration of the related paramagnetic species would be increased/decreased upon trapping/release of the electron associated to the formation/filling of oxygen vacancy. The influence of Ti impurities on the PL and RPE signals was investigated. Finally, it is concluded that the EPR signal is related to oxygen vacancies and its position shift could be explained by the involvement of some mixing orbitals. Thanks to static (PL and EPR) and dynamic (EPR) in situ characterizations, the conditions of formation or filling of oxygen vacancies are discussed depending of the atmosphere and temperature of the pretreatment of kadox and ex-carbonate zinc oxide. High temperature treatments, inert atmospheres, and vacuum lead to the formation of new oxygen vacancies. This process is reversible upon oxygenated atmospheres. The efficiency of such filling up depends on the temperature and starts to prevail on the oxygen vacancy formation below 500 K. It is also shown that few native oxygen vacancies can also be filled up.

Correlation between structural and electronic order–disorder effects and optical properties in ZnO nanocrystals

“…3, we can observe that the EPR signal intensity increases under UV-LED illumination, and this behavior can be associated with structural and electronic order-disorder effects of both Zn or O atoms. These values are similar to those previously reported in the literature, [47][48][49][50] and a review of the subject has been reported by Hunger and Weitkamp. 56 To understand, the origins of the EPR signal could be assigned to the holes trapped on oxygen atoms, in particular, oxygen vacancies at the particle surface or bulk.…”

“…[46][47][48][49][50] According to the literature, this EPR signal can be associated with possible defects that are induced in the ZnO lattice, as zinc vacancies (V Zn ), oxygen on interstitial sites (O i ), mobile electrons either in the conduction band and/or shallow donor states and oxygen vacancies ðV z O Þ. [46][47][48][49][50] However the latter is the defects most commonly accepted for this EPR signal and are assigned to singly ionized oxygen vacancy defects ðV þ1 O Þ. This is evidenced by UV-light irradiation that produces an increase in the EPR signal and is related to oxygen vacancy concentrations.…”

Investigation of physical properties of screen printed nanosized ZnO films for optoelectronic applications

“…The derivative signals have g-values ∼ 1.9964 in both the films powder. This signal corresponds to singly ionized oxygen vacancies present in ZnO lattice [38,39] which are formed in these films during growth process when oxidation of zinc takes place by the atmospheric air during sintering process. As the g-value is less than free electron g-value of 2.0023 which indicates the donor origin of the paramagnetic centre.…”

On the origin of white photoluminescence from ZnO nanocones/porous silicon heterostructures at room temperature

“…First, we note that the signal at g = 1.96, typically observed in ZnO in many morphologies [24,[38][39][40], is absent from our spectra (it was not observed for any of the samples studied). The g = 1.96 resonance has been attributed to O vacancies [24,[38][39][40], and hence associated with strong luminescence in the visible from ZnO [40,41].…”