Figure 7

MIR emission spectra of α-NaYF₄:5%Er³⁺ nanocrystals calcined at different temperatures for 2 h.

Insert: sample photos of α-NaYF₄:5%Er³⁺ nanocrystals calcined at different temperatures for 2 h. The 0 °C stands for as-prepared α-NaYF₄:5%Er³⁺ nanocrystals.