Lifetime of excited Cu+ in alkali halides

An experimental study is made of the time decay of excited Cu+ ions diluted in potassium halides in order to determine the role of the host crystal in the impurity absorption and emission processes. The Cu+ ions are responsible for a few ultraviolet absorption bands which, after optical stimulation, give rise to emission at ≈︁ 4000 Å. The lifetime, τR, of the lowest excited state, presumably 3d94s, is measured and found to be ≈︁ 50 μs in KCl:Cu, ≈︁ 100 μs in KBr:Cu and ≈︁ 5 μs in KI:Cu). The thermal de‐excitation energies, ΔEd, are also measured and found to be ≈︁ 0,73 eV (KCl:Cu), ≈︁ 0,76 eV (KBr:Cu), ≈︁ 0,61 eV (KI:Cu). These results together with measurements of other workers may suggest that the transition 3d10 ≈︁ 3d94s, forbidden in the free ion, becomes partially allowed due to the crystal field. The implications of an off‐centre position of the Cu+ ion inthe K+ vacancy are also discussed and found to be consistent with the experimental data.