Lifetime studies on excited (F₂⁺)* and M centers in NaF doped with magnesium

Abstract

The lifetime and the decay properties of the relaxed excited state (RES) of the (F2+)* center in NaF:Mg are investigated: similarities with the F2+ center RES in pure NaF are once more evidenced. Nevertheless, two strange new effects are found: a) the radiative quantum yield is an increasing function of temperature up to 300 K; b) the (F2+)* luminescence can be induced by light excitation in the M center absorption band, in spite of the apparent absence of (F2+)* levels which can absorb in this spectral range. Furthermore, an absence of perturbative effects by magnesium ions on the decay properties of the M centers is ascertained.

The absence of energy transfer between F and M centres in alkali halides: the case of NaF

“…Furthermore, we want to stress that we obtained the same behaviour that had been found previously by Bosi and Nimis [24] for the quantum yield of the M luminescence in x-ray coloured NaF:Mg samples: in fact, they ascertained the absence of perturbative effects by magnesium ions on the decay properties of the M centre (in particular, no change of the lifetime value). In any case, for the sake of comparison, we present in figure 3 both I corr (M 1 ) and (M F ) data for the NaF:Li additively coloured sample (present work) together with the ones, I Mg (M 1 ), previously obtained [24] in the NaF:Mg sample by light excitation in the M 1 band (please note that the data are normalized to unity at the lowest T in order to obtain the relative quantum yield).…”

“…As a further proof we recall that, as anticipated, the absolute quantum yield of the F luminescence decreases as a function of the absolute (initial) concentration as well as of the local F-centre concentration (an ageing effect which implies the shortening of the distance between F centres) but the F-centre luminescence lifetime is unchanged. This seems to be a general rule for the F centre in alkali halides: as regards the NaF case, we refer to the papers of Bosi et al [3 (see, for instance, figure 7), 21,22,24]. Nevertheless, we recall the existence of another effect: the change of the F-centre lifetime as a consequence of the interaction between F and α centres.…”