Key points are not available for this paper at this time.
The small-particle limit for scattering by spheres (Rayleigh scattering) has an upper limit on the refractive index. Also, the limiting expression for perfectly reflecting spheres has a lower limit on the refractive index. These limits are delineated here for both absorbing and nonabsorbing spheres.
Kerker et al. (Sun,) studied this question.