It is suggested that a broad absorption band which occurs in additively coloured CaF₂ at 521 nm and in additively coloured SrF₂ at 595 nm is a superposition of absorptions from two types of F₂ centre, one oriented along (100) and the other along (110). Broad emission bands of the two types of centre are also superimposed, peaking in CaF₂ at 585 nm and in SrF₂ at 644 nm. Under high resolution a zero phonon line of the (110) oriented F₂ centre is observed at 20K in both emission and absorption bands; it occurs in CaF₂ at 539.6 nm and in SrF₂ at 605.3 nm, The excitation spectra for both the zero phonon line emission and the broad band emission have been investigated and their polarization properties established. Both the zero phonon line and the broad absorption band may be made dichroic by bleaching with linearly polarized light at 77K; this treatment produces preferential alignment of the centres. The destruction of the dichroism by thermally induced disorientation has been studied. Optical pumping gives rise to a reduction of intensity of absorption of F₂ centres due to population of metastable excited states; the lifetimes of these states have been measured. Uniaxial stress measurements on the zero phonon lines show that the centres involved have orthorhombic I symmetry and that the dipole moment of the transition is along (100). The zero phonon lines also show a large linear Stark effect. From the combined stress and Stark measurement it follows that the point symmetry of the centres giving rise to the zero phonon lines is C_2v.