  Photoluminescence, thermally stimulated luminescence (TSL) and EPR
characteristics of the Ce3+ doped single crystals of multicomponent
Y1Lu2GaxAl5-xO12 and Lu3GaxAl5-xO12 garnets with different Ga contents (x = 0,
1, 2, 3, 4, 5) excited in the Ce3+ - related absorption bands are investigated
in the 9 - 500 K temperature range. The distribution of Ga3+ and Al3+ ions in
the crystal lattice is determined by the NMR method. The relative number of
Ga3+ ions in the tetrahedral crystal lattice sites, the maxima positions of the
TSL glow curve peaks and the corresponding trap depths are found to decrease
linearly with the increasing Ga content. At the same time, the reduction of the
activation energy Ea of the TSL glow curve peaks creation under irradiation in
the 4f - 4d1 absorption band of Ce3+ is strongly nonlinear. To explain this
effect, the suggestion is made that Ea is the energy distance between the
excited 5d1 level of Ce3+ and a defect level located between the 5d1 level and
the bottom of the conduction band and arising from the Ga3+ ion perturbed by
the nearest neighboring Ce3+ ion. The electrons thermally released from the
excited Ce3+ ions are suggested to be trapped at the perturbed Ga3+ ions
resulting in the appearance of electron Ga2+ centers. In spite of the fact that
the paramagnetic Ga2+ ions were not detected by EPR, the described above
process was found for Fe3+ impurity ions, namely the electron transfer from the
5d1 excited levels of Ce3+ to Fe3+ was directly detected by EPR.
