Eliminate of colour center and growth of large-size Tb3Ga5O12 crystals

•Large-size TGG with Φ76 mm * L100 mm crystals were successfully grown.•The vacancy defect of Ga causes the change of Tb valence in TGG crystal.•Increasing the content of Ga2O3 in raw material can eliminate the color center.•Annealing can eliminate color center and improve optical properties of crystals. A series of large-size TGG single crystals with Φ76 mm * L100 mm were grown successfully by Czochralski (Cz) method. The formation mechanism of colour center was discussed and the results show the colour center of TGG crystals is strongly related with composition of atmosphere and raw material. The large-size TGG crystals with only light-yellow colour center can be obtained by increasing the content of Ga2O3 in the melt. In order to improve the optical properties of crystal, the suitable annealing conditions for TGG crystals were also studied for the first time. The results show the common colour center of TGG crystals can be eliminated by selecting suitable annealing conditions. And the as-grown TGG crystals have good transmittance of 80% and extinction ratio over 35 dB after annealing, which means that it can well meet the current requirements for the application of magneto-optical devices.