High quantum efficiency YbAG-crystals

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2007

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In this work, the growing process of Yb-doped YAG crystals is modified to achieve stoichiometric YbAG samples with a minimum quenching of the Yb3 +-fluorescence. The best samples were grown by the Czochralski technique from rhenium-crucibles under reducing atmosphere (H2 + N2). The as-grown YbAG crystals are of light blue color due to Yb2 +-centers. The fluorescence lifetime of Yb3 + after annealing the YbAG crystals under oxidizing atmosphere is 862 ± 15 μ s. The non-annealed samples show strong quenching of the Yb3 +-fluorescence with a lifetime of only a few tens of microseconds depending on the actual growth conditions. This strong quenching is partially attributed to the Yb2 +-centers giving rise to a cooperative energy transfer process among two excited Yb3 +-ions and one non-excited Yb2 +-ion. Typical quenching centers in Yb:YAG crystals grown from Ir-crucibles are Fe- and Ni-impurities. Another effective quenching center in non-annealed crystals is a complex center consisting of a Si2 +-ion and a charge compensating oxygen vacancy with one trapped electron (F+color center). This type of center was identified by ESR- and ENDOR-measurements. © 2006 Elsevier B.V. All rights reserved.

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Forschungsinformationssystem der UHH

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