Structure of YAG Crystals Doped/Substituted with Erbium and Ytterbium

Two series of yttrium aluminum garnets doped with erbium and ytterbium ions have been studied by single-crystal
X-ray diffraction. The single crystals were obtained by the Czochralski method. The concentration of doping ions
was established by the plasma emission spectroscopy method. For the Er series, it is equal to 23.4, 46.7, 72.5,
and 100%, whereas, for Yb-doped YAGs, it equals 26.5, 48.2, 75.9, and 100%. The results are supplemented by
the data obtained for pure YAG. The X-ray data for all samples were collected at two temperatures:  295(2) and
102(2) K. Additionally, for YAGs doped with ca. 50% of doping ions, some more detailed temperature measurements
were performed. Pure single crystals of ErAG and YbAG were also studied as a function of diffraction angles.
Careful single-crystal measurements utilizing a CCD diffractometer revealed the unit cell parameters, which slightlybut significantlydeviate from cubic symmetry. The average unit cell parameters change linearly with the amount
of substituting Er and Yb cations, with two different slopes related to the ionic radii. Both of the dodecahedral
distances depend linearly on the concentration of the substituting ions, but the longer dodecahedral distance also
changes with temperature contrary to the shorter one. There is no correlation between the octahedral interatomic
distance [Al(VI)···O] and the unit cell parameter or temperature; however, weak trends appear for the tetrahedral
[Al(IV)···O] distance. Such weak trends are just the secondary consequences of the ion substitution taking place
at the dodecahedral site. The dependences between the unit cell parameters and the concentration of doping ions
allow us to establish concentrations of particular doping ions in mixed (Er, Yb) doped YAGs just on the basis of
the measured unit cell parameters and knowledge of the amount of Y.