Lu3Al5O12:Ce3+ (LuAG:Ce) is a scintillator with a fast response time. The light yield is lower than theoretically expected and to increase the light yield co-doping with Pr3+ is investigated. To better understand the energy flow to the Ce3+ ion, first low temperature emission and excitation spectra of Pr3+ doped LuAG were investigated, allowing the accurate determination of the zero-phonon lines for the 5d states of Pr3+ in LuAG and the temperature dependent energy transfer from the Self Trapped Exciton to Pr3+. In addition VUV excitation and soft X-ray excited emission spectra of the co-doped LuAG:Ce,Pr were studied. The results show that energy transfer from Pr3+ to Ce3+ occurs but it is followed by back transfer to the 4f states of Pr3+.