Abstract
AbstractEmission by FA(II)‐centres in alkali halides is investigated by treating the centre as a molecule immersed in a dielectric medium. The molecule consists of a single electron in the field of two unit positive charges and a central anion of effective charge (‐Ze). Its ground and first excited states are estimated variationally as a function of interionic separation and of Z. Lattice relaxation is treated in the rigid point‐ion model with Coulomb and nearest‐neighbour Born‐Mayer interaction. Only displacements of the saddle‐point ion and its two nearest neighbours are considered. These displacements determine Z, which gives a single‐parameter characterization of the defect. Three new FA(II)‐CentreS are postulated, namely in NaF:Li, RbF:Li, and RbF:Na, and their emission energies are estimated from a semi‐empirical scheme to be 0.915, 0.513, and 0.591 eV, respectively.
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