Upconversion nanoparticles with active shell exhibit high thermometry sensitivity in water

Nanoscale fluorescence thermometry based on upconversion nanoparticles (UCNPs) has recently attracted much attention. Here we report that UCNPs with active shell exhibit high thermometry sensitivity in water. UCNPs with NaGdF4:Yb,Tm,Mn/NaYF4:Yb active core/active shell were successfully synthesized, while the temperature is determined based on the fluorescence intensity ratio of 475 nm (1G4 -> 3H6) and 450 nm (1D2 -> 3F4) of Tm3+. These active core/active shell nanoparticles show a thermometry sensitivity of 0.048/K in aqueous environment, which is higher than 400% of that (0.012/K) in the environment without water molecules. This is ascribed to selective quenching of 450 nm (1D2 -> 3F4) emission band relative to the 475 nm (1G4 -> 3H6) band of Tm3+ by water, while the separated quenching and emission processes in active core/active shell structure avoid the simultaneous quenching of 450 nm and 475 nm bands. The high thermometry sensitivity of these nanoparticles is also confirmed in the temperature monitoring of plant cells.

Automated summary

Nanoscale fluorescence thermometry based on upconversion nanoparticles (UCNPs) with active shell shows high sensitivity in water. The fluorescence intensity ratio of Tm3+ at 475 nm (1G4 -> 3H6) and 450 nm (1D2 -> 3F4) is used to determine the temperature. The active core/active shell nanoparticles exhibit a thermometry sensitivity of 0.048/K in aqueous environment, which is 400% higher than that in the environment without water molecules. This enhanced sensitivity is attributed to selective quenching of the 450 nm emission band by water and the separated quenching and emission processes in the active core/active shell structure.