  Within the effective mass approximation and variational method the effect of
dielectric constant mismatch between the size-quantized semiconductor sphere,
coating and surrounding environment on impurity binding energy in both the
absence and presence of a magnetic field is considered. The dependences of the
binding energy of a hydrogenic on-center impurity on the sphere and coating
radii, alloy concentration, dielectric-constant mismatch, and magnetic field
intensity are found for the GaAs-Ga_(1-x)Al_(x)As-AlAs (or vacuum) system.
