Monitor local structure variation of Ce³⁺ activator in YAG:Ce nanophosphor with calcination temperature by nuclear magnetic resonance spectroscopy

Understanding the intrinsic relationship between photoluminescence (PL) properties and fine crystal structure is essential for developing excellent cerium doped Y₃Al₅O₁₂ (YAG:Ce) nanophosphors. Herein, we studied the crystal structure evolution of YAG:Ce nanophosphors with calcination temperature via multiple characterization techniques, and focused on clarifying the local structure of Ce³⁺ activator by advanced quantitative ²⁷Al magic angle spinning nuclear magnetic resonance (²⁷Al MAS NMR) spectroscopy. The results showed that the crystallinity of the YAG:Ce nanophosphors was improved and the lattice constant monotonously decreased with rising calcination temperature. Especially, as the calcination temperature increased from 830 to 1030 °C, more Ce³⁺ ions entered the first sphere of AlO₆ groups and the symmetry of AlO₄ species gradually increased in YAG:Ce nanophosphors, which caused the decrease of geometrical distortion surrounding Ce³⁺ activators. Due to the variations of fine structure, the PL intensity obviously increased with calcination temperature while its position remained constant. When the calcination temperature further increased to 1080 °C, CeO₂ impurity formed in the nanophosphor, resulting in the increase of the quenching centers.