title: Ratiometric highly sensitive luminescent nanothermometers working in the room temperature range. Applications to heat propagation in nanofluids.
abstract: 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 Eu(3+) and Tb(3+) 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' Eu(3+)/Tb(3+) 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.
authors.affiliation: Departamento de Física and CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Carlos D S
authors.initials: CD
authors.lastname: Brites
authors.forename: Patrícia P
authors.initials: PP
authors.lastname: Lima
authors.forename: Nuno J O
authors.initials: NJ
authors.lastname: Silva
authors.forename: Angel
authors.initials: A
authors.lastname: Millán
authors.forename: Vitor S
authors.initials: VS
authors.lastname: Amaral
authors.forename: Fernando
authors.initials: F
authors.lastname: Palacio
authors.forename: Luís D
authors.initials: LD
authors.lastname: Carlos