THE LOWER EXCITED-STATES OF A CU- LOCALIZED OR NOT( IMPURITY IN NAF )

The lowest excited states of a Cu+ impurity in NaF are studied with Ha rtree-Fock-Roothaan calculations on large embedded clusters. Attention is focussed on the question of how localized these excitations are. T he interest in the nature of the excited states has recently revived, because it was concluded from OD-EPR experiments on the luminescent st ate of Cu+ in NaF, that there is almost no electron spin density in Cu 4s. However, one- and two-photon absorption spectra on the Cu+ impurit y in NaF have been interpreted in terms of localized Cu+(3d(10)) to Cu +(3d(9)4s(1)) excitations. Our results suggest that low lying states e xist, in which the excited electron and the electron hole are only loo sely coupled.