Effect of air annealing on the color center in Yb:Y3Al5O12 transparent ceramics with MgO as sintering additive

• High quality Yb:YAG transparent ceramics were fabricated with MgO as sintering aids.
• The Yb:YAG samples were annealed at 1250–1450 °C for 20 h in air.
• The complex color center [Mg2+F+] formed during the annealing.
• The complex color center can be eliminated after post-HIP.

High quality Yb:Y3Al5O12 (YAG) transparent ceramics were fabricated by vacuum sintering with MgO as sintering aids. The Yb:YAG samples were annealed at 1250–1450 °C for 20 h in air. The experimental results showed that the transparency of Yb:YAG samples declined markedly with the annealing temperatures of 1250–1450 °C. The samples became increasingly orange-yellow in color with the increase of annealing temperature. The potential reasons of discoloration were discussed for the first time. It was attributed to the complex color center [Mg2+F+] formed during the annealing, which was evidenced by optical absorption in the range of 300–500 nm wavelength and the presence of an electron spin resonance (ESR) line at g = 1.9806. The formation mechanism of the complex color center was explained in detail. The complex color center can be eliminated after post-HIP (hot isostatic pressing). And by air annealing and post-HIP, the transmittance of the samples increased from 80.3% to 83.4%.