We investigate scintillation properties and energy trapping processes in Pr-doped Lu3Al5O12 (Pr:LuAG) optical ceramics, specifically focusing on the effects of sintering aids. Ceramics with good transmittance and scintillation properties comparable with those of single crystals were obtained without the use of sintering aids. Their introduction caused a transparency improvement, accompanied, however, by a deterioration of scintillation properties in terms of light yield and time decay. We interpret the results, discussing the role of aliovalent sintering agents on the formation of point defects acting as traps affecting the transport of charge carriers to the luminescence centers.