Temperature-dependent spectroscopic analysis of F 2+** and F 2+**-like color centers in LiF

Abstract

A temperature-dependent spectroscopic analysis of the color center laser medium, LiF : F 2 +**, is shown. Special attention is devoted to the well-known F 2 +** color center as well as a new F 2 +**-like color center, conclusively discovered in this work, which is found to have a peak absorption near λ abs 0=80 8 nm and peak emission near λ ems 0=108 0 nm . Justification for the association of this new center with F 2 +**-like color centers is explained in the text. Standard F 2 +** color centers have kinetics of fluorescence lifetime of τ 13 K =32 ns , τ 300 K =21 ns , for a quantum efficiency of fluorescence, η=66%. Concerning the new F 2 +**-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 F 2 +**-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.