Fluorescence line narrowing of trivalent praseodymium in lanthanum trifluoride single crystal—Phonon-induced relaxation

Phonon-induced relaxation of Pr³⁺: LaF₃ is studied by a fluorescence-line-narrowing technique at temperatures from 4 to 50 ^∘{}K. For temperatures exceeding 15 ^∘{}K the theory fits the data within the experimental error. For the lowest temperatures, however, mechanisms other than phonon-induced relaxation must contribute to the linewidth. Several such mechanisms are discussed.