On the optical properties of undoped and rare-earth-doped yttrium aluminium garnet single crystals

摘要

Optical absorption and photoluminescence (PL) measurements were performed on single crystals of undoped Y _3Al _5O _(12) (YAG) and a number of rare-earth-doped YAG to study the effect of dopant type and concentration, growth atmosphere, post-growth annealing and UV irradiation on the optical properties of YAG crystals. The presence of hydrogen in the growth atmosphere was found to be essential for enhancing the incorporation of Ce ions in the Ce ~(3+) state in Ce-doped YAG (Ce:YAG). Annealing in air was shown to have no effect on the PL emission of Ce:YAG crystals. An absorption peak around 256nm was observed in the undoped YAG and Ce:YAG crystals after air anneal at 1200°C. Optical absorption and annealing experiments support the association of the 256nm peak with Fe impurities and oxygen ions. UV irradiation modifies the valency of impurities and generates electronic defects leading to an increase in the optical density of YAG crystals. Optimizing the growth and annealing conditions is critical in order to develop Ce:YAG single crystals as efficient scintillators.