Anomalous europium luminescence in LaF3

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 LaF3-Eu2+ contains not only asymmetric weakly structured band at 245 nm but also less intense bands at 330, 380 nm. Broadband Eu2+ emission at 600 nm appeared below 80 K with decay time 2.2 mu s at 7.5 K. Emission at 600 nm is attributed to so-called anomalous luminescence. Bulk conductivity is directly proportional to absorption coefficient of Eu2+ bands. Dielectric relaxation peak of LaF3-EuF3 is attributed to rotation of dipoles Eu2+-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. (C) 2016 Elsevier Ltd. All rights reserved.