Investigation of intrinsic and extrinsic defects in solid solution Gd3(Al,Ga)5O12 crystals grown by the Czochralski method

Mixed garnet crystals with nominal stoichiometry Gd3Al2.5Ga2.5O12 undoped, single doped with Sm3+, Ho3+, Er3+ and Yb3+ and co-doped with Ho3+ + Yb3+ and Er3+ + Yb3+ were grown by the Czochralski method. Optical spectra and thermal conductivity of obtained single crystal samples were measured and analyzed. Recorded optical absorption spectra revealed that the intensity and spectral characteristics of color centre absorption in the UV region, close to the UV absorption edge of the host, are affected by the type of incorporated rare earth ions. On the other hand, spectral characteristics of stable color centers induced by an intense UV irradiation of crystals depend weakly on the rare earth admixture. Low temperature optical spectra provided the evidence that Sm3+ ions and Er3+ ions occupy at least two different types of sites in this host but Yb3+ ions seem to be located preferentially in identical sites. Thermal conductivity of the crystals at 300 K, weakly affected by incorporated rare earth ions, is comparable to that reported for ordered gallium gadolinium garnet crystals. At cryogenic temperatures, i.e. below ca 80 K, thermal conductivities of the crystals containing rare earth ions are markedly smaller than that of undoped one, however.