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

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. © 2013 The Royal Society of Chemistry.We acknowledge Fundaçao para a Ciência e a Tecnologia (FCT, Portugal), COMPETE and FEDER programs (Pest-C/CTM/LA0011/2011, PTDC/CTM/101324/2008) and Integrated Spanish–Portuguese Action PT2009-0131 for financial support. The work in Zaragoza has been supported by the grants MAT2011-25991 and CONSOLIDER CSD2007-00010 from the Ministry of Economy and Competitivity. CDSB (SFRH/BD/38472/2007) and PPL (SFRH/BPD/34365/2006) thank FCT for grants. NJOS acknowledges FCT for the Ciência 2008 program.Peer Reviewe