Figure 7.

(a) Red emission normalized luminescence spectra of QBC939 cells (incubated with UCNPs) under 980 nm excitation at different pH. (b) Variation of the relative luminescence intensity ratio of 475 nm to 645 nm at different pH values: (c,d) images of the QBC939 cell’s nucleus under 405 nm excitation; (e,f) the upconversion images of different sites in single cell upon 980 nm light excitation; and (g,h) merged images of (c&e) and (d&f), respectively, in 10 µm scale bar. (i) The upconversion emission spectra of (e,f) sites of the cell, normalized at 645 nm (Reproduced from Ref. [30], Creative Commons license: http://creativecommons.org/licenses/by/4.0/).