High-pressure optical absorption spectroscopic measurements of both erbium-doped and undoped Si nanoparticles have been carried out in a diamond anvil cell up to pressures of 180 kbar. The emphasis here is with respect to (a) the effect of particle size on the pressure dependence of the band gap as well as (b) indirect examination of the structural impact of the erbium dopant on the pressure-induced phase transition(s). It is found that in terms of electronic structure these Er-doped Si nanocrystals act very much like indirect gap silicon, with an observed band gap pressure dependence of -1.4 x 10(-6) eV/bar. Measurements of the optical spectra in terms of integrated area as a function of pressure of these doped nanoparticles reveal that the first-order phase transition must lie above 180 kbar, substantially elevated from the bulk value of 120 kbar. Thus, doped nanocrystals of this dimension maintain a significant elevation in the phase transition pressure (known in homogeneous Si nanocrystals relative to bulk crystalline Si), but the Er dopant does not introduce the type of structural defects that would lower the energy barrier to such a transformation.