The field dependence of the low temperature infrared fluorescence of Ni2+in MnF2up to 110 kG is reported and the changes occurring at the spin‐flop transition at 94 kG are analyzed. These are accounted for by an upward shift of the fluorescent state energy of 16.7 cm−1and a modification of the ground term splittings. Both effects are shown to arise from the flip of the sublattice magnetizations from the [001] to the [100] directions. From the measured shift of the excited state the exchange energy for the3T2term is estimated to be about 110 cm−1.