MR-to-VIS upconversion mechanisms upon excitation into I-4(11/2) around 980 nm in the Er3+ doped low energy phonon host material RbGd2Br7 are identified and analyzed. The small energy difference between the first excitation step I-4(15/2)-->I-4(11/2) and the second step I-4(11/2)-->F-4(7/2) leads to a competitive situation of excited state absorption and energy transfer upconversion processes. Their relative efficiency strongly depends on the excitation energy and temperature. Fingerprinting techniques based on the temporal evolution of the upconverted luminescence after a IO ns laser pulse are used to distinguish the two mechanisms. Rate constants for the relevant processes are determined. With W-t = 68 s(-1) at 10 K the energy transfer step in the upconversion process is comparable to Er3+ doped CsCdBr3.