Effect of Oxygen Vacancies on the Mechanoluminescence Response of Magnesium Oxide
Ekaterina Novitskaya, Aaron Manheim, Manuel Herrera, Olivia A. Graeve
Abstract
The mechanoluminescence response of oxide materials has implications for the use of these materials in structural health monitoring applications, where crack propagation needs to be monitored. Thus, we describe the mechanoluminescence of MgO powders, showing that the signal is dependent on the existence of oxygen vacancies. Cathodoluminescence (CL) spectra of the powders exhibited an emission at 2.10 eV associated with F+ centers (oxygen vacancies), as well as intense CL emissions at 3.70 and 4.10 eV, associated with M+ and M– centers (paired-oxygen vacancies). Furthermore, CL measurements revealed an emission at 1.70 eV, which was not influenced by mechanical stress and can be attributed to an electronic transition between excited and ground F+ states. The presence of oxygen vacancies was confirmed by X-ray photoelectron spectroscopy and electron energy loss spectroscopy. Measurements of CL intensity with respect to electron irradiation time confirmed the presence of high amounts of F+ centers, as well as a saturation time effect in which emission intensity achieves a maximum only after a certain time of irradiation. The existence of this saturation effect was correlated to the mechanoluminescence signal.