Exciton Bohr radius ($a_X=4\pi {ϵ}_0{ϵ}_r{\hslash }^2/({\mu }^{\ast }{e}^2)$)

The characteristic relative-motion length of a hydrogenic Wannier-Mott exciton, with dielectric screening and exciton reduced mass ${\mu }^{\ast }$. Comparing a quantum dot's dimensions with this scale helps distinguish strong carrier confinement from confinement of a comparatively intact bound pair.