Defect-induced electric fields in ZnS

The optical absorption edge in cubic ZnS shows both phonon- and impurity-induced effects which determine its precise shape. Applying external electric fields and measuring the shift of the absorption edge makes it also possible to compute the impurity excitonic mass which was found to be ? 0.02m₀. Comparing the edge shifts due to the impurity-induced electric fields with those due to the external fields, one finds the approximate value for the average impurity-induced field as being about 3 × 10⁴ V/cm.