Zero-Phonon Lines and Phonon Coupling in ZnS:Mn

The optical absorption and emission spectra of several ZnS:Mn crystals (0.07 to 1.0 mole%) were obtained at 4.2 and 77\ifmmode^\circ\else\textdegree\fi{}K. Fine structure was observed in all bands. The predominant structure was identified in terms of phonon emission coupled to one electronic transition in each band. Zero-phonon lines were found at 17 891, 19 683, 21 237, 22 638, and 25 297 ${\mathrm{cm}}^{\ensuremath{-}1}$. They should correspond to transitions between some levels of the cubic crystalline field---terms such as $^{6}A_{1}\ensuremath{\rightarrow}^{4}T_{1}$, $^{6}A_{1}\ensuremath{\rightarrow}^{4}T_{2}$, $^{6}A_{1}\ensuremath{\rightarrow}^{4}E$, $^{6}A_{1}\ensuremath{\rightarrow}^{4}A_{1}$, etc. Principal phonons participating are of energies of about 86, (183,263), 298, and 340 ${\mathrm{cm}}^{\ensuremath{-}1}$. Possible mode assignments are pointed out. In conclusion, we suggest that the usually observed widths and shape of manganese bands are due predominantly to phonon coupling.