AbstractIon implantation followed by rapid thermal annealing is used to induce layer intermixing and thus selectively blue-shift the emission wavelength of InP-based quantum well hetero- structures. The intermixing is greatly enhanced over thermal intermixing due to the supersaturation of defects. The magnitude of the observed blue-shift has been studied previously as a function of ion fluence and ion mass: the dependence on ion mass is well established, with heavier ions producing a larger shift. We show here that chemical effects can also play a significant role in determining the induced blue-shift. Data are presented from the implantation of the similar mass ions; aluminum (m~27), silicon (m~28) and phosphorus (m~31). The P- induced blue shift displays a monotonic increase with fluence, consistent with previous studies; however, the fluence dependence of Al- and Si-induced blue-shifts both deviate significantly from the behaviour for P. These results have important implications for attempts to scale intermixing behaviour with ion mass.