As Sadiq said, the linear-optical-absorption coefficient of doped metals may affected by doping with nanomaterials.In most cases, the linear optical absorption of such metals changes in a nonlinear manner.
It depends upon the metal to be doped and wavelength to be scanned. It can vary if transition or rare metals are doped. However, sub ppm level may cause (any) change in mu, linear absorption coefficient, needs to be investigated.