Effect of annealing on the optical properties of Nd:YAG transparent ceramics

The Nd:YAG transparent ceramics were fabricated by vacuum sintering at 1750 °C for 20 h, where the raw nanopowders were synthesized by a modified co-precipitation method. Subsequently the Nd:YAG ceramic specimens were annealed or even re-annealed in air or vacuum at 1250–1500 °C for 20 h. The Nd:YAG ceramic specimens were investigated by X-ray diffraction, ultraviolet spectroscopy, inductively coupled plasma atomic emission spectroscopy, electron paramagnetic resonance spectroscopy and scanning electron microscopy. The results showed that post-annealing could improve the optical properties and microstructure of Nd:YAG transparent ceramics. By air annealing, the in-line transmittances of the specimens increased, mainly due to the decrease of oxygen vacancies concentration in specimens. The air annealing at 1450 °C for 20 h was optimum for preparation of Nd:YAG transparent ceramics. Furthermore, the red shift of UV absorption edge after air annealing could be attributed to the absorption by Fe3+ charge transfer bands.

► The air annealing at 1450 °C for 20 h is optimum for preparation of Nd:YAG transparent ceramics.
► By air annealing, the in-line transmittances of Nd:YAG specimens increase, mainly due to the decrease of oxygen vacancies concentration in specimens.
► The red shift of UV absorption edge after air annealing should be attributed to the absorption by Fe3+ charge transfer bands.
► The absorption by Fe3+ charge transfer bands together with some scattering centers has contributed to the decrease of transmittance at λ < 400 nm.