Effect of annealing on microstructure and luminescence characteristics in spark plasma sintered Ce³⁺-activated (Gd, Lu)₃Al₅O₁₂ garnet ceramics

In the case of spark plasma sintered (SPSed) oxides, it is known that carbon contamination and oxygen vacancies are introduced during the sintering process due to the SPS characteristic of a carbon-rich environment. The introduction of carbon contamination and oxygen vacancies had a direct effect on the transmittance, and the annealing process mostly recovered the low transmittance of sintered bodies. It also affected the luminescence characteristics. The luminescence intensity of sintered bodies, which was very low due to carbon contamination and oxygen vacancies, could be dramatically improved through the annealing process. In the specimens with longer holding times during SPS, the grain size was increased, and the porosity was also significantly reduced, resulting in higher intensity improvements. Through the SPS process, the sintered body was effectively densified, and the annealing could compensate for the drawback of SPS and enable better luminescence properties.