Defect properties of Ce-doped and undoped YAG crystals were studied by Doppler broadening of positron annihilation γ-rays and thermoluminescence (TL) as a function of temperature (25–300C). 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 decreased with increasing temperature up to 100C, and then increased with temperature. The TL intensity in Ce-doped YAG showed the opposite behavior to L+. The results indicated that point defects probed by positrons may be responsible for the energy transfer to Ce ions and TL intensity. Possible defects detected by positrons were negatively charged or neutral defects related to impurity antisites, cation vacancies, and vacancy complexes.

Point Defects in Ce-Doped Y3Al5O12 Crystal Scintillators. C.L.Wang, D.Solodovnikov, K.G.Lynn: Physical Review B, 2006, 73[23], 233204 (4pp)