It was noted that the properties of many defects in ionic solids exhibited systematic variations, as a function of the lattice parameter of the host crystal, which reflected a corresponding scaling of the defect wave functions. Previous studies had suggested that F-center wave functions scaled in direct proportion to the inter-ionic separation. However, this conflicted with both experimental and simulation results. It was shown here that a linear scaling of the wave functions was applicable to the 1-electron model ground states of many electron-excess defects, in highly ionic materials, including substitutional ions and F-center family defects. It was concluded that this explained the wide range of exponents that were found for defect optical absorptions that satisfied the Mollwo-Ivey relationship, as well as the existence of exponents that were greater than the so-called classical limit of 2.

M.S.Malghani, D.Y.Smith: Materials Science Forum, 1997, 239-241, 365-8