Optical and nonradiative transitions involving triplet states of laser-active F3+ colour centres in LiF crystals

Spin triplet electronic states in laser-active F₃⁺ colour centres in LiF crystals were found. The triplet — triplet spectra of the absorption from the ³E state to higher triplet states (³[IMG align=ABSMIDDLE alt=${\mathit\Gamma}$]uiop[/IMG]_α,³[IMG align=ABSMIDDLE alt=${\mathit\Gamma}$]uiop[/IMG]_β), the spectrum of the triplet — triplet ³[IMG align=ABSMIDDLE alt=${\mathit\Gamma}$]uiop[/IMG]_α → ³E fluorescence, and the spectrum of the phosphorescence accompanying the triplet — singlet intercombination ³E → ¹A₁ transition were determined. Moreover, the temperature dependences of the probabilities of nonradiative singlet — triplet (¹E → ³E) and triplet — singlet (³E → ¹A₁) transitions were determined. An analysis was made of the influence of spin triplet states on the characteristics of an LiF : F₃⁺ laser. A method was proposed for tunable lasing in a wide visible range as a result of a triplet — triplet transition in the F₃⁺ colour centres in an LiF crystal.