The luminescence spectra of Eu3+ doped in a series of double perovskite lattices Ba2LnMO6 (Ln = Y, Gd; M = Nb, Ta) have been recorded at room temperature and 10 K. Together with FT-IR and FT-Raman spectra and aided by DFT vibrational energy calculations, assignments have been made for the crystal field levels of the 5DJ (J = 0,1) and 7FJ (J = 0–2) multiplets. The luminescence spectra are consistent with monoclinic symmetry of these systems. The crystal field parameters from the fitting of the energy level data set of Ba2YNbO6:Eu3+ enable the crystal field strength to be calculated, and the order of magnitude is Cl– < O2– < F– for the EuX6n– (n = 6 for halogen, 9 for oxide) moieties. For these systems, an empirical linear relationship between crystal field strength and electronegativity of ligand X has been found. By contrast, the nephelauxetic series from the depression of the Slater parameter F2 is Cl– ≈ O2– > F– > free ion for these systems. Copyright © 2012 American Chemical Society. Copyright © 2012 American Chemical Society.