High quantum efficiency YbAG-crystals

In this work, the growing process of Yb-doped YAG crystals is modified to achieve stoichiometric YbAG samples with a minimum quenching of the image-fluorescence. The best samples were grown by the Czochralski technique from rhenium-crucibles under reducing atmosphere image. The as-grown YbAG crystals are of light blue color due to image-centers. The fluorescence lifetime of image after annealing the YbAG crystals under oxidizing atmosphere is image. The non-annealed samples show strong quenching of the image-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 image-centers giving rise to a cooperative energy transfer process among two excited image-ions and one non-excited image-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 image-ion and a charge compensating oxygen vacancy with one trapped electron (imagecolor center). This type of center was identified by ESR- and ENDOR-measurements.