Anomalous europium luminescence in LaF3

Abstract Optical spectra (absorption, emission, excitation, decay) and dielectric relaxation were measured for divalent europium and partially for ytterbium in lanthanum fluoride crystals. Optical absorption of LaF 3 –Eu 2+ contains not only asymmetric weakly structured band at 245 nm but also less intense bands at 330, 380 nm. Broadband Eu 2+ emission at 600 nm appeared below 80 K with decay time 2.2 μs at 7.5 K. Emission at 600 nm is attributed to so-called anomalous luminescence. Bulk conductivity is directly proportional to absorption coefficient of Eu 2+ bands. Dielectric relaxation peak of LaF 3 –EuF 3 is attributed to rotation of dipoles Eu 2+ -anion vacancy. The long-wavelength absorption at 300–400 nm region are assigned to transitions from 4f 7 Eu 2+ ground state to states of neighbouring fluorine vacancy.