FLi center

The fabrication of lasers based upon color centers adds a further dimension to the laser wavelengths available. Ordinary F centers do not exhibit laser action, but F centers that have a dopant cation next to the anion vacancy are satisfactory. These are typified by FLi centers, which consist of an F center with a lithium ion neighbor (Fig. 9.26a). Crystals of KC1 or RbCl doped with LiCl, containing FLi centers have been found to be good laser materials yielding emission lines with wavelengths between 2.45 and 3.45 p,m. A unique property of these crystals is that in the excited state an anion adjacent to the FLi center moves into an interstitial position... 

Figure 9.26 FLi color centers in KC1 (a) ground-state Fu center and (b) excited-state type II FLi center responsible for laser output.

The color of diamond due to nitrogen impurities has been described in Section 9.6.3 It has been found that nitrogen impurities that are located next to a carbon vacancy in diamond thin films endow the solid with quite new properties, somewhat similar to the properties of a solid containing FLi centers compared with ordinary F centers. The diamond structure is built up of carbon atoms each surrounded by four... 

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