  We report direction dependent luminescence (DDL), i.e., the asymmetry in the
luminescence intensity between the opposite directions of the emission, in
multiferroic CuB2O4. Although it is well known that the optical constants can
change with the reversal of the propagation direction of light in multiferroic
materials, the largest asymmetry in the luminescence intensity was 0.5 % so
far. We have performed a measurement of photoluminescence with a He-Ne laser
irradiation (633 nm). The luminescence intensity changes by about 70 % with the
reversal of the magnetic field due to the interference between the electric
dipole and magnetic dipole transitions. We also demonstrate the imaging of the
canted antiferromagnetic domain structure of (Cu,Ni)B2O4 by using the large
DDL.
