Fluctuating fluorescence of single color centers in lithium fluoride crystals

Single F$_2$- and F$_3^+$- color centers in the LiF crystal were studied by confocal fluorescence microscopy. The time dependences of their fluorescence intensity were analyzed and statistically processed. Our studies show that, the F$_3^+$- color center, being photoexcited, is able enter the triplet state, while in ground (singlet) state it changes orientation with a frequency of 1.5–2 Hz at room temperature, due to reorientational diffusion, unlike the F$_2$- center, which is reoriented only being in the triplet state. This subtype of rotational diffusion of the center does not lead to its translational diffusion.