OPTICAL-PROPERTIES OF THE OXYGEN-PERTURBED F-2+ COLOR-CENTERS IN 6 DIFFERENT ALKALI-HALIDES

We studied the formation and optical properties of (F2+)H centres in six different crystals doped with oxygen: NaCl, KCl, KBr, RbCl, RbBr and KI. The results are entirely new in the case of KI and mostly original for RbCl and RbBr. The absorption and emission bands are compared with those of pure F2+ centres in similar host lattices. In order to obtain an interpretation of the relationship between the wavelengths of the low-energy transitions 1ssigma(g) <----> 2ppi(u) and the nature of the host crystal, we applied a semi-empirical model based on the analogy of F2+-like centres to molecular hydrogen ions immersed in a dielectric medium. This model, with the influence of both lattice parameter and dielectric constant, explains nicely the experimental results, including those for KI, which are inadequately described in the framework of the simpler Mollwo-Ivey law.