The as-prepared double-perovskite Ba2LaNbO6 (space group 12/m at ambient temperatures) exhibited an unexpected well-resolved red luminescence, which was found to arise from parts-per-million impurity of Mn4+. The ions Mn4+ or Cr3+ doped into this host are situated at Nb5+ sites with slightly distorted octahedral symmetry, with the distortion greater for the case of greater charge mismatch. The Stokes luminescence spectra of the dopant ions comprise nu(3), nu(4), and nu(6) moiety mode vibronic origins, and the high vibrational frequency ratio nu(4)/nu(3) signals the stiffness of the O-M-O (M = Mn, Cr) angle in the double perovskite. The site symmetry at the La3+ site of lanthanide ions doped into Ba2LaNbO6 comprises a 2-fold axis at most. All dopant ions exhibit concentration quenching in this lattice.