Fig. 8. (a) Schematic design of a Ce³⁺ doped Er-RENPs. (b) TEM and HRTEM images. (c) The luminescence spectrum of the Er-RENPs with or without 2% Ce³⁺ doping. (d) Schematic illustration outlining the surface modification of the Er-RENPs. (e) The luminescence spectrum of oleic acid-capped Er-RENPs dispersed in cyclohexane and Er-RENPs@PMH-PEG dispersed in water. (f) The photostability of Er-RENPs@PMH-PEG in PBS and FBS solutions. (g) Color photograph of a C57BI/6 mouse. (h) and (i) time-course NIR-IIb brain fluorescence images showing the perfusion of RENPs into various cerebral vessels. (j) Cerebral vascular image in the NIR-IIb region with corresponding PCA overlaid image. (k) SBR analysis of the NIR-IIb cerebrovascular image. Reproduced from ref. 132 with permission from Springer Nature.