The excited-state structure of impurity-trapped excitons are measured in a multisite system. We use a two-color (UV-IR) pulsed photoluminescence enhancement technique, which probes the interlevel transitions and dynamics of impurity-trapped excitons in doped insulating phosphor materials. The technique is applied to NaMgF${}_{3}$:Yb${}^{2+}$, which exhibits emission from two charge-compensation centers with peaks at 22300 cm${}^{\ensuremath{-}1}$ (448 nm) and 24000 cm${}^{\ensuremath{-}1}$ (417 nm). The observed photoluminescence enhancement is caused by a combination of intraexcitonic excitation and electron trap liberation. The electron traps are inferred to have a depth of approximately 800 cm${}^{\ensuremath{-}1}$.