Approximate widths of zero phonon lines broadened by point defect strain fields

In 1967 Stoneham showed how the width of a zero phonon line may be determined from the strain field of point defects in the crystal. The direct application of the theory is difficult because of the need to evaluate numerically a two-dimensional integral. It is shown here how the integral may be trivially evaluated to within a few per cent for any zero phonon transition between non-degenerate electronic states. The method exploits the change in linewidth which results from the defects being forbidden to approach closer than some minimum distance to the optical centres. This change is found to be approximately the same for all transitions between non-degenerate levels.