Fig. 1. XRD patterns of (a) NaYF₄:20%Yb³⁺/2%Ho³⁺ and (b) LiYF₄:20%Yb³⁺/2%Ho³⁺ microcrystals. (a) NaYF₄:20.0%Yb³⁺/2.0%Ho³⁺微米晶体和(b) LiYF₄:20.0%Yb³⁺/2.0%Ho³⁺微米晶体的XRD图谱

Fig. 2. The SEM images of (a) NaYF₄:20%Yb³⁺/2%Ho³⁺ and (b) LiYF₄:20%Yb³⁺/2%Ho³⁺ microcrystals. (a) NaYF₄:20.0%Yb³⁺/2.0%Ho³⁺微米晶体和(b) LiYF₄:20.0%Yb³⁺/2.0%Ho³⁺微米晶体的SEM图谱

Fig. 3. Schematic illustration of confocal microscopy setup.共聚焦显微光谱测试系统示意图

Fig. 4. Upconversion emission spectra and corresponding optical micrographs of single NaYF₄:20%Yb³⁺/2%Ho³⁺ and LiYF₄:20%Yb³⁺/2%Ho³⁺ microcrystal under local excitation at 980 nm (100 mW/cm²). 在980 nm激光激发下, 单颗NaYF₄:20.0%Yb³⁺/2.0%Ho³⁺微米晶体和LiYF₄:20.0%Yb³⁺/2.0%Ho³⁺微米晶体的上转换发射光谱图(激发功率为100 mW/cm²)

Fig. 5. (a), (b) Upconversion emission spectra and corresponding optical micrographs, (c), (d) the peak area of the green and red emission intensity and corresponding R/G ratio of single NaYF₄:20%Yb³⁺/2%Ho³⁺ (a), (c) and LiYF₄:20%Yb³⁺/2%Ho³⁺ (b), (d) microcrystal with excitation power densities increasing from 20 mW to 100 mW. 在980 nm激光激发下, 单颗粒(a) NaYF₄:20.0%Yb³⁺/2.0%Ho³⁺微米晶体和(b) LiYF₄:20.0%Yb³⁺/2.0%Ho³⁺微米晶的上转换发射与其激发功率的依赖关系, 插图为其对应光谱图案; (c)和(d)为对应不用激发功率下的峰面积, 插图为其随激发功率变化的红绿比图

Fig. 6. (a), (b) UC emission spectra and corresponding optical micrographs, (c), (d) the peak area of the green and red emission intensity and corresponding R/G ratio of cluster NaYF₄:20%Yb³⁺/2%Ho³⁺ (a), (c) and LiYF₄:20%Yb³⁺/2%Ho³⁺ (b), (d) microcrystals with excitation power densities increasing from 20 mW to 100 mW. 在980 nm激光激发下　(a) NaYF₄:20.0%Yb³⁺/2.0%Ho³⁺微米粉末和(b) LiYF₄:20.0%Yb³⁺/2.0%Ho³⁺微米粉末的上转换发射与其激发功率的依赖关系, 插图为其对应发光光谱图案; (c)和(d)为对应不用激发功率下的峰面积图, 插图为其随激发功率变化的红绿比图

Fig. 7. Energy level diagrams and proposed energy transfer pathways.Ho³⁺离子相应的能级图及其可能跃迁机理图

Fig. 8. (a) Downconversion emission spectra and (b) emission mechanism of single NaYF₄:20%Yb³⁺/2%Ho³⁺ and LiYF₄:20%Yb³⁺/2%Ho³⁺ microcrystal under laser 532 nm excitation. 在532 nm激发下, 单粒NaYF₄:20.0%Yb³⁺/2.0%Ho³⁺微米晶体和 LiYF₄:20.0%Yb³⁺/2.0%Ho³⁺微米晶的下转换发射光谱(a)及相应跃迁机理图(b)