Point defects in Ce-doped Y3Al5O12 crystal scintillators

Defect properties of Ce-doped and undoped Y3Al5O12 (YAG) crystals were studied by Doppler broadening of positron annihilation gamma rays and thermoluminescence (TL) as a function of temperature (25-300 degrees C). The positron diffusion length L+ was evaluated mainly from the S parameter versus positron energy. Compared with undoped YAG, Ce-doped YAG has a smaller positron diffusion length, due to its higher density of defects. L+ in Ce-doped YAG decreases with increasing temperature up to 100 degrees C, and then increases with temperature. The TL intensity in Ce-doped YAG shows the opposite behavior to L+. The results indicate that point defects probed by positrons may be responsible for the energy transfer to Ce ions and TL intensity. Possible defects detected by positrons are negatively charged or neutral defects related to impurity antisites, cation vacancies, and vacancy complexes.