Thermally stimulated exoelectron emission (TSEE) was studied for MgO single crystals. First, the TSEE response was measured for annealed or quenched samples. Some samples were ion-implanted by H+, He+ or Al+; then, after thermal annealing, the TSEE showed an increase relative to the non-implanted samples. This process was dependent on the element, energy and implanted dose. After a few reading cycles the TSEE of the ion-implanted samples started to decrease. However, upon re-annealing it increased once more. This showed that a fraction of the newly produced centers could be stabilized using a proper, yet still unknown, thermal treatment.