Optical Properties of $\alpha -\mathrm{M}\mathrm{n}\mathrm{S}$

Optical characteristics of $\alpha -\mathrm{M}\mathrm{n}\mathrm{S}$ have been determined from 0.02 to 14 eV. Single crystals were used for measurements above 0.05 eV. The shift with temperature of the ${}_{}{}^6{}_{}{}^{}A_{1g}^{}{}_{}{}^{}\to {}_{}{}^4{}_{}{}^{}A_1^{}{}_{}{}^{}$ crystal-field splitting peak is shown to be reasonably attributed to the effect of magnetic ordering. A broad weak band near 1 eV may be either an impurity band or the unallowed transition $\mathrm{Mn}\left(3\mathrm{}{d}^{++}\right)\to \mathrm{Mn}\left(3\mathrm{}{d}^{+}\right)$. The absorption edge at 2.8 eV is explained as due to transitions from the wide ${\mathrm{S}}^{2-}\mathrm{}\left(3p\right)\mathrm{}$ band to the narrow ${\mathrm{Mn}}^{+}\mathrm{}\left(3d\right)\mathrm{}$ band. Two tiny peaks in the edge at 2.96 and 3.05 eV are suggested to be zero-phonon spin-orbit-split exciton peaks associated with this transition. High-energy absorption structure taken from Kramers-Kronig analysis of ultraviolet reflectance data are assumed to be associated with wide-band to wide-band transitions as in nonmagnetic compounds. A simple band diagram is suggested to explain the electronic transitions. The reststrahlen reflectance on a pressed powder was analyzed and the following parameters obtained: low- and high-frequency dielectric constants, 20 and 6.8; longitudinal and transverse optical mode frequencies, 320 and 185 ${\mathrm{cm}}^{-1\mathrm{}}$.