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Ratiometric highly sensitive luminescent nanothermometers working in the room temperature range. Applications to heat propagation in nanofluids

2013; Royal Society of Chemistry; Volume: 5; Issue: 16 Linguagem: Inglês

10.1039/c3nr02335d

2040-3372

Carlos D. S. Brites, Patrícia P. Lima, Nuno J. O. Silva, Ángel Millán, V. S. Amaral, Fernando Palacio, Luís D. Carlos,

Transition Metal Oxide Nanomaterials

There is an increasing demand for accurate, non-invasive and self-reference temperature measurements as technology progresses into the nanoscale. This is particularly so in micro- and nanofluidics where the comprehension of heat transfer and thermal conductivity mechanisms can play a crucial role in areas as diverse as energy transfer and cell physiology. Here we present two luminescent ratiometric nanothermometers based on a magnetic core coated with an organosilica shell co-doped with Eu3+ and Tb3+ chelates. The design of the hybrid host and chelate ligands permits the working of the nanothermometers in a nanofluid at 293–320 K with an emission quantum yield of 0.38 ± 0.04, a maximum relative sensitivity of 1.5% K−1 at 293 K and a spatio-temporal resolution (constrained by the experimental setup) of 64 × 10−6 m/150 × 10−3 s (to move out of 0.4 K – the temperature uncertainty). The heat propagation velocity in the nanofluid, (2.2 ± 0.1) × 10−3 m s−1, was determined at 294 K using the nanothermometers' Eu3+/Tb3+ steady-state spectra. There is no precedent of such an experimental measurement in a thermographic nanofluid, where the propagation velocity is measured from the same nanoparticles used to measure the temperature.