Point Defects as Precursors of Electron-Hole Centers: Systematics and Theories of Radiation Centers in Minerals

Abstract

Many of the local (point) defects in solids are paramagnetic or can be made so, and hence are amenable to study by electronic paramagnetic resonance (EPR) as well as by optical spectroscopy. In many cases, it is convenient to classify these into two general types: missing-electron species and excess-electron species, as compared to some diamagnetic precursor. The concept of holes is useful when the number of electrons is insufficient to fill a given atomic or molecular orbital. Typically, when one more electron is required for this completion, i.e., one negative charge is missing (this is theoretically equivalent to the presence of a hypothetical positive charge), then one can speak of the existence of a hole in the orbital, and treat this as a physically meaningful entity. It is fruitful to speak of the paramagnetism and EPR spectrum of such a hole. However, the concept is not universally valuable, e.g., for species H⁰ and Fe³⁺ which have half-filled shells.