Figure 6

Decay curves of fresh (red, dotted line) and DMEM-aged (red, solid line, red) 20 nm bare UCNP and fresh (dotted line, blue) and H2O-aged (straight line, blue) 20 nm UC-citrate nanoparticles. The aged UCNP were collected and redispersed in milli-Q water for the measurement of the decay kinetics. The Yb3+ emission was excited at 976 nm and detected at 1010 nm.