Fig. 1. Tanabe--Sugano energy level of Cr³⁺ in octahedral crystal field^[29]

Fig. 2. Schematic diagrams of cell surface polysaccharide detection based on Cr-PLNPs-PEG avidin^[41]. (a) Preparation and detection principle of Cr-PLNPs-PEG avidin; (b) ConA, WGA and PNA expression on DU145H cells and RWPE-1 cells; (c) ConA, WGA and PNA expression on DU145 cells before and after treating tunicamycin

Fig. 3. Application of Cr-PLNPs in vivo imaging^[48]. (a) Application diagram; (b) persistent image and decay curve of Cr-PLNPs after photo-stimulated by LED

Fig. 4. Cr-PLNPs-NH₂ used for in vivo targeted imaging^[47]. (a) Synthesis, functionalization and in vivo imaging of Cr-PLNPs-NH₂; (b) application of ZGO-TAT in cell targeted imaging in vitro; (c) application of ZGO-FA in vivo targeted imaging

Fig. 5. Cr-PLNPs applied to multimodal imaging^[58]. (a) NGR-ZGGO∶Cr, Pr@TaO_x@SiO₂ with core-shell structure; (b)excitation and emission spectra, persistent attenuation images of NGR-ZGGO∶Cr, Pr@TaO_x@SiO₂; (c) CT images (inset) and CT values of NGR-ZGGO∶Cr, Pr@TaO_x@SiO₂ with different mass concentrations

Fig. 6. Cr-PLNPs applied to PDT^[59]. (a) Synthesis of Cr-PLNPs-SiPc; (b) absorption spectra of Si-Pc and emission spectra of Cr-PLNPs; (c) tumor growth curve after PDT

Fig. 7. Lipo-Cr-PLNP-PTX used for imaging guided therapy^[63]. (a) Synthesis of Lipo-Cr-PLNP-PTX; (b) persistent luminescence imaging of Lipo-Cr-PLNP-PTX; (c) growth curve of tumor after chemotherapy

Fig. 8. Cr-PLNPs-CuS-RGD used for imaging guide PPT^[62]. (a) Synthesis of Cr-PLNPs-CuS-RGD; (b) in vivo imaging of Cr-PLNPs-CuS-RGD; (c) tumor growth curve after PTT

Fig. 9. TAT@Eu/Cr-PLNPs used to track ASC^[38]. (a) Preparation of TAT@Eu/Cr-PLNPs; (b) comparison with QDs and dye in vivo imaging of TAT@Eu/Cr-PLNPs

Fig. 10. Cr-PLNPs used for imaging of metastatic tumors and PDT adjuvant chemotherapy^[78]. (a) Synthesis route of DSPLNPs@hSiO₂@CCM; (b) imaging and PDT adjuvant chemophototherapy in vivo controlled by 808 nm laser with DSPLNPs@hSiO₂@CCM