Fig. 1. XRD patterns of NaYF₄:Yb³⁺/Tb³⁺（Yb³⁺∶Tb³⁺=20∶1）

Fig. 2. XRD patterns of NaYF₄:Yb³⁺/Tm³⁺（Yb³⁺∶Tm³⁺=10∶1）

Fig. 3. Scanning electron microscope (SEM) images of NaYF₄:Yb³⁺/Tb³⁺(Yb³⁺/Tb³⁺=10∶1)particles and Energy Dispersive X-Ray Spectroscopy(EDS)

Fig. 4. Scanning electron microscope (SEM) images of NaYF₄:Yb³⁺/Tm³⁺ （Yb³⁺∶Tm³⁺=15∶1）particles and Energy Dispersive X-Ray Spectroscopy (EDS)

Fig. 5. The emission spectrum of NaYF₄:Yb³⁺/Tb³⁺under the excitation of 980 nm

Fig. 6. Energy level transition diagram of Yb³⁺/ Tb³⁺

Fig. 7. The emission spectrum of NaYF₄:Yb³⁺/Tm³⁺under the excitation of 980 nm

Fig. 8. Energy level transition diagram of Yb³⁺/Tm³⁺