Optical properties of fluorite-type crystals with MA color centers

Measurement of Oscillator Strengths of “F2A” Centres in MeF2:A+ (Me = Ca, Sr; A+ = Li+, Na+, K+)

“…Unfortunately, for these two crystals, t o the best of our knowledge, the only fluorescing centre with a measured lifetime (36 ns) is F2 in CaF, [14]. Using (6), with the values of Eabs and Efluo from literature and with grc = g, = 1, we obtain./ = 0.063) which is quite smaller than the values of Table 1 for the " F 2 A " centre in doped CaF,. This is an extra evidence that "F2g" centres in doped crystals are not Fz centres close to an alkaline impurity.…”

“…They are reproducible to 0.01, but, of course, their accuracy may be worse because of unsuspected systematic errors. For instance, if the oscillator strength of the F band in KC1 is different from our assumed 0.85 (see Table 3 (6), using the data of [6].…”

“…Since the Stokes shift is relatively small for "FZA" centres, the electronic wave functions are probably not very different in the non-relaxed and in the relaxed excited states and the matrix element of the dipole operator should be nearly the same in absorption and emission. We therefore use the simplified version (6) of Fowler and Dexter's formula, together with the lifetime data of [6]2) to obtain the f,-values listed in the last column of Table 1. I n the case of SrF,:K+, the excited state lifetime has not yet been measured, to the best of our knowledge.…”