Previous steady-state and time-resolved luminescence spectroscopy of 3p1P1 atomic magnesium, isolated in thin film samples of the solid rare gases, is extended to include the higher energy 4p1P1 excitation. Well-resolved site splittings are recorded in Mg/Ar samples for excitation to the 4p1P1 level. A small red shift in the absorption energy to the 4p1P1 level for Mg/Ar contrasts with a small blue shift on absorption to the 3p1P1 level. Direct emission from the 4p1P1 level is not observed in any of the rare gas matrices; instead, intense emission from the low energy 3p1P1 level is. Measurements of the emission decay curves in Mg/Ar have revealed slow rates in the steps feeding the 3p1P1 level following 4p1P1 excitation. The reason for the differential shifting of the 4p1P1 and 3p1P1 levels as well as the lack of direct 4p1P1 emission is thought to be related to the strong binding interaction between Mg in the 4p1P1 state and the rare gases.