โ Scribed by Leonardo Bosi; Daniela Gallo; Marco Zelada
No coin nor oath required. For personal study only.
The fluorescence of the Cu + impurity centre in NaCI was investigated in the range 19-300 K. Accurate lifetime and quantum yield measurements partially contradict the results obtained in the past by Pedrini. Contrary to what happens in the potassium halides the Cu + de-excitation mechanism cannot be interpreted simply in terms of the Pedrini model (two excited states in thermal equilibrium are involved in the emission process, one of which is metastable and lies close below the emitting level). The discrepancies are supposed to be related to the instability of the on-centre configuration of Cu + in NaC1.
In several host matrices Cu + does not occupy the position of the ion it substitutes, but goes towards an 'off-centre' position. The forecast for off-centre displacement was achieved [1]; nevertheless, it can be noted that the position in the lattice of Cu รท in the relaxed excited state (RES) could be different from that in the ground state.
Pedrini investigated [2,3] the lifetime ~-(T) as a function of temperature T of Cu + in LiCI (harmonically on-centre) and NaC1 (anharmonically on-centre) and assumed that the data can be fairly well explained by the presence of a metastable level lying close below the emitting level. Consequently, he forecast the following ~-(T) dependence:
๐ SIMILAR VOLUMES