Excitation und deexcitation of Tm 3+ centres in ZnS involving “External” Excited States

The excitation and thermal quenching behaviour of two Tm 3+ centres in ZnS crystals are studied by measuring broad‐band excitation spectra and the temperature dependence of the decay time, (τ), of the blue 1 G 4 , → 3 H 6 , emission of samples with different codopants. It is shown that these centers possess “external” excited states which manifest themselves by excitation peaks and τ( T ) dependences characteristic of the centre investigated. Values are given of the transfer rates from the external to the 4f states, which lie between 10 10 and 10 12 s −l . It is believed that the occurrence of external states is a general property of RE 3+ centers in 11‐VI compounds and that these states, in many cases, have a crucial effect on luminescence yield.