Trapped-hole centers in alkaline-earth oxides

Alkaline-earth oxides frequently exhibit a visible coloration when stimulated with photons or ionizing radiation. The defects responsible for this coloration are often due to paramagnetic hole centers which absorb over a broad spectrum in the visible and near-visible region. As a result, the defects can be detrimental to the use of these materials as hosts for tunable lasers. In this article, we present our current understanding of trapped-hole (or V-type) centers in the alkaline-earth oxides with emphasis on experimental research using optical and magnetic resonance techniques. Discussions are focused on the production mechanisms, the structure of both intrinsic and impurity-compensated defects, and their thermal stability. (author)