fig4

Figure 4. (A) Schematic diagram of the ML mechanism and energy transfer for SrAl₁₂O₁₉: Cr³⁺, Nd³⁺ (or Yb³⁺ or Er³⁺ or Yb³⁺, Er³⁺); (B) ML spectra of SrAl₁₂O₁₉:2%Cr³⁺, 1%Nd³⁺ (or 1%Yb³⁺ or 1%Er³⁺ or 1%Yb³⁺, 5%Er³⁺) samples employed a visible-NIR detector (600-1,000 nm); (C) ML spectra of SrAl₁₂O₁₉:2%Cr³⁺, 1%Nd³⁺ and (D) ML spectra of SrAl₁₂O₁₉:2%Cr³⁺, 1%Er³⁺ using a NIR detector (900-1,700 nm). ML: mechanoluminescence; NIR: near-infrared.