The number of electrons emitted per impinging ion is known to be very high for hydrogenated B-doped diamond films. However, following ion bombardment the yield of emitted electrons rapidly decreases due to structural and chemical changes induced by the irradiation process. These changes eventually result in negative electron affinity loss and graphitization of the diamond film. Here we report results on ion-induced electron emission (IIEE) from undoped, sub-micron thick and hydrogenated diamond films. We found that the IIEE properties of these films are more stable upon similar bombardment conditions as compared to those of micron and sub-micron thick B-doped films. The enhanced IIEE properties of the sub-micron films are most likely associated with a reduced charging.