Wide band-gap semiconductors have become an important base material for applications in optoelectronics and in high power, high temperature electronics. After doping with various rare earths, electroluminescence throughout the whole visible spectrum has been observed. We have studied the implantation behaviour of the rare earth Lu in ZnO. Our samples were implanted at the ISOLDE facility at CERN. In order to recover the sustained implantation damage the samples were treated in a rapid thermal annealing furnace. In a first attempt to measure the temperature dependence of the electric field gradient at the site of 172Lu/172Yb in ZnO a large jump in the quadrupole interaction frequency was observed between measurements at room temperature and 200°C. Above 200°C the frequency only changed very little. In order to understand this unusual behaviour we prepared another sample and studied the temperature range between room temperature and 200°C in more detail. The results obtained previously could be confirmed. The new data show a smooth increase of the quadrupole interaction frequency from about 146 MHz at room temperature to almost 390 MHz at 400°C. This behaviour is likely to be due to the influence of the rare earth's partially filled 4f shell.