Exciton and Interband Spectra of Crystalline MnF_2*

Abstract

Reflection and absorption spectra of MnF2 (crystals were kindly supplied by F. Legend, Center for Nuclear Studies at Saclay, France, and V. Saccarino, University of California, Santa Barbara, California) in the region from 4.5 to 31 eV were investigated at room and liquid-nitrogen temperatures. Peaks associated with the onset of allowed transitions are explained in terms of excitons at r (10.48 and 10.55 eV) and at X (10.24 eV) and on this basis some features of the band structure are proposed. Splitting of these peaks is interpreted in terms of the spin-orbit splitting of p-like valence bands arising primarily from F- ions. The energy-loss spectrum contains peaks corresponding to plasma frequencies of electrons in half-filled d-like bands and in F- valence bands. Transitions over the range from 4.5 to 9.5 eV are ascribed to d excitons associated with states 6S(d5) → 4F(d5), 6D(d4s), and 4D(d4s) of the Mn2+ ion in an orthorhombic crystal-ligand field.