The present work contains results on study of color centers in YAlO₃ (YAP) and Gd₃Ga₅O₁₂ (GGG) crystals both pure and activated with various dopants. By the origin the color centers in the crystals studied can be divided on growth CC (observed in as-grown crystals) and induced CC (created in crystals as a result of temperature treatments or irradiation).
The growth coloration of GGG crystals is caused by [V_OV_Ga]^- complexes and Fe³⁺ impurity (absorption near 37000 cm^-1), complex centers [CaF⁺], [CaO^-] and [Gd_octaO^-] (absorption near 29000 cm^-1) as well as F-centers (23000 cm^-1).
The growth coloration of YAP crystals (wide absorption band in the 48000-20000 cm^-1 range with several maxima) is caused by color centers formed as a result of deviation of crystal composition from the stoichiometric one (R=Y₂O₃/Al₂O₃>1) and presence of uncontrolled impurities such as Ca, Mg and Fe.
By the time stability at room temperature the induced CC can be divided on stable and transient CC. By the mechanism of formation they can be divided on ionization and radiation displacement ones. The stable coloration is caused by recharging of growth CC present in the crystals as well as formation of the radiation displacement defects by the impact mechanism.
The stable CC in the crystals studied can be O^- centers localized near defects in cation sublattice, F-centers and [V_OV_C]^- complexes. The transient CC can be F⁺-centers and self-trapped O^- centers that absorb near 15000 cm^-1. Influence of activator ions on the processes of CC formation is analyzed.
GGG:Nd active media are more radiation resistant in comparison with YAP:Nd crystals, therefore they and can be used in solid-state lasers for space applications.

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1. Thermal expansion of NdGaO₃ perovskite
2. Crystal structure and thermal expansion of PrGaO₃ in the temperature range 10-1253 K
3. Color centers in YAP:Pr crystals
4. Thermoluminescence of doped YAlO₃ crystals
5. Twin structure of LSGMO crystals studied by Laue method