Interstitial fluorine ion

Przybylinska et al. (1992) proposed a model for the TL of Cdp2 Eu. It is based on extensive studies using OA, PL and TL. Out of 17 types of complex centers of various symmetries only two were foimd to take part in the TL. These were the Eu -Og and Eu -Fj" complexes (Ol stands for a substitutional oxygen and Fj" is an interstitial fluorine ion). Annealing of the crystal at 500°C in fluorine was found to show an OA and PL emission at 290 run and aimealing in oxygen resulted in a band at 260 nm. These... 

Figure 9.6 (a) Representation of a MF2 unit cell (M = Ca, Cd, Pb, Sr). The black circles represent cations. For the sake of clarity, F anions, which sit at the corner of each small cube, are not represented on this figure, (b) Representation of the unit cell when doped with Ln. The interstitial fluorine ion compensating the positive charge can for example be situated along the < 100> direction or along the <111>... 

Mg-inhibition. Even if sediments or interstitial waters are at or near saturation with phosphate, there are still impediments to CFA crystallization. One of the most significant is the role of Mg-inhibition. Martens and Harris (1970) demonstrated in the laboratory that when phosphate and fluorine are added to a solution with a composition similar to that of ocean water in Mg VCa ratio, apatite does not crystallize. Instead, a Ca-phosphate gel precipitates with a Ca/P ratio of 1.35 compared to the ratio of 1.67 found in apatite. In their experiments, the gel was kept in the proxy seawater solution for 8 months with no appearance of apatite. However, when the gel was placed in a Mg-free solution, apatite quickly formed. Mg-inhibition results from the smaller Mg ion replacing Ca in the apatite structure, the resultant lattice distortion prevents effective crystal growth (Martens and Harris 1970). Later work by Gulbrandsen et al. (1984) showed that given enough time, in their experimentation seven years, apatite would indeed crystallize from the gel despite the Mg in solution. 

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