Optical absorption and
photoluminescence (PL) measurements were performed on single crystals of
undoped Y3Al5O12 (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 Ce3+ 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 256 nm 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 256 nm 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.
Source:IOPscience
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