Reflectance, luminescence and Raman experiments on Eu3+ crystal field transitions in Eu2BaZnO5

Three spectroscopic techniques have been combined to resolve the complex problem of Eu3+ crystal field levels in Eu2BaZnO5.Eu3+ luminescence has been investigated in the off-resonance condition for several excitation energies as a function of temperature. Raman phonons and several Raman crystal field transitions are obtained. From reflectance experiments (between 1.25 and 3.7 eV), 5D multiplet levels are determined. The schemes of the lowest electronic levels of both Eu3+ sites have been established combining data from these three spectroscopies which show a good agreement with the calculated values. Crystal field parameters are obtained in an approximation to a C2v local symmetry. The high value of fourth-rank parameters indicates a partial covalent character of Eu-O bonds. The obtained spin-orbit coupling value, ζ = 1280(70) cm-1, is similar to those in other europium oxides. The variation of the Raman crystal field transition intensity with temperature presents an unexpected deviation with respect to the ground state population, specially pronounced in the low temperature range. The peaks corresponding to the three highest levels of the 7F2 multiplet are anomalous probably due to some hybridization with the nearest oxygen levels. The relative intensity of luminescence peaks associated with transitions from 5D0 and 5D1 levels vary versus temperature as a function of the probability of the non-radiative decay. We propose a mechanism that can explain the observation of anti-Stokes luminescence even at low temperatures. (author)