High quantum efficiency YbAG-crystals

Abstract In this work, the growing process of Yb-doped YAG crystals is modified to achieve stoichiometric YbAG samples with a minimum quenching of the Yb 3 + -fluorescence. The best samples were grown by the Czochralski technique from rhenium-crucibles under reducing atmosphere ( H 2 + N 2 ) . The as-grown YbAG crystals are of light blue color due to Yb 2 + -centers. The fluorescence lifetime of Yb 3 + after annealing the YbAG crystals under oxidizing atmosphere is 862 ± 15 μ s . The non-annealed samples show strong quenching of the Yb 3 + -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 Yb 2 + -centers giving rise to a cooperative energy transfer process among two excited Yb 3 + -ions and one non-excited Yb 2 + -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 Si 2 + -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.