Temperature-dependent spectroscopic analysis of F2+** and F2+**-like color centers in LiF

A temperature-dependent spectroscopic analysis of the color center laser medium, LiF : F2+**, is shown. Special attention is devoted to the well-known F2+** color center as well as a new F2+**-like color center, conclusively discovered in this work, which is found to have a peak absorption near λabs0=808 nm and peak emission near λems0=1080 nm. Justification for the association of this new center with F2+**-like color centers is explained in the text. Standard F2+** color centers have kinetics of fluorescence lifetime of τ13 K=32 ns, τ300 K=21 ns, for a quantum efficiency of fluorescence, η=66%. Concerning the new F2+**-like color center, the 13 K lifetime was found to be τ≈5 ns. We show that Alexandrite laser radiation can simultaneously excite the absorption bands of both F2+**-like centers in their region of spectral overlap. The resulting emission from both centers is the mechanism responsible for the ultrabroadband range of tunability, ∼800–1300 nm, from this laser medium at RT. This crystal is the heart of a potential ultrabroadband, near-IR laser; frequency doubling this fundamental output will realize a truly white-light laser.