Table 1. Photochemical and Photophysical Parameters Showing the Advantages of UCNPs in Imaging Compared to Dyes and QDs.

parameter	days	QDs	UCNPs
emission fwhm	50 nm	20–50 nm	<20 nm
decay magnitude	1 ns	10 ns	100 μs
photobleaching	fast	slow	none
photoblinking	yes	yes	no
multiphoton excitation power (W/cm2)	106–109	104–106	1–103