Absorption spectra of MgF2 and AlF3 in the region of the Mg and Al Lsub(2,3) excitations

The absorption spectra of thin films of MgF2 and AlF3 were measured in the region of the Mg and Al Lsub(2,3) excitations using synchrotron radiation. The spectrum for MgF2 is similar to that previously reported, but with two differences. The lowest energy (exciton) structure is resolved into two peaks leading to new values of the spin-orbit and exchange splitting, 0.33 and 0.21 eV, respectively, and there are a number of peaks in the original spectrum that were not obtained. The AlF3 spectrum shows that these arose from AlF3 contamination of the original films. The AlF3 spectrum bears a striking resemblance to that of MgF2, indicating that critical point structures probably play no role. Structure in the first exciton peak is not resolved in the absorption spectrum but thermotransmission spectra reveal a splitting of 0.44 eV. (author)