UV and Temperature-Sensing Based on NaGdF4:Yb3+:Er3+@SiO2–Eu(tta)3

A multifunctional nanosystem was synthesized to be used as a dual sensor of UV light and temperature. NaGdF 4 :Yb 3+ :Er 3+ upconverting nanoparticles (UCNPs) were synthesized and coated with a silica shell to which a europium(III) complex was incorporated. The synthesis of NaGdF 4 UCNPs was performed via thermal decomposition of lanthanide ion fluoride precursors in the presence of oleic acid. To achieve sufficient water dispersibility, the surface of the hydrophobic oleate-capped UCNPs in the hexagonal phase was modified by a silica coating through a modified Stöber process through a reverse microemulsion method. An Eu(tta) 3 (tta: thenoyltrifluoroacetonate) complex was prepared in situ at the silica shell. A dual-mode nanothermometer was obtained from a near infrared to visible upconversion fluorescence signal of Er 3+ ions together with UV-excited downshifting emission from the Eu 3+ complex. Measurements were recorded near the physiological temperature range (293-323 K), revealing excellent linearity ( R 2 > 0.99) and relatively high thermal sensitivities (≥1.5%·K -1 ). The Eu(tta) 3 complex present in the silica shell was tested as the UV sensor because of the Eu 3+ luminescence dependence on UV-light exposure time.