Figure 2

(a) Overlay of 1D ²⁷Al MAS NMR spectra for Al₂O₃, Er-doped Al₂O₃, un-doped α-Al₂O₃ phase and un-doped θ-Al₂O₃ phase. The MAS rate was equal to 10 kHz. (b) 2D ²⁷Al MQ-MAS spectra of un-doped Al₂O₃ (c) 2D ²⁷Al MQ-MAS spectra of Er-doped Al₂O₃.