Sampling Sub-Diffraction Temperature Gradients with Spectrally Orthogonal Nanoparticle Luminescence.

Area of Science:

• Nanotechnology
• Optical Physics
• Materials Science

Background:

• Optical thermometry using single nanoparticles offers sub-diffraction spatial resolution but is limited to single-point measurements.
• Probing temperature gradients requires multi-point measurements, which is challenging with conventional methods.

Purpose of the Study:

• To develop a multi-point optical thermometry technique capable of resolving temperature gradients within sub-diffraction regions.
• To utilize spectrally orthogonal luminescence from different nanoparticle species for simultaneous temperature sensing.

Main Methods:

• Employed lanthanide-doped upconverting nanoparticles (UCNPs) with spectrally distinct, temperature-dependent luminescence (NaYF4:Yb3+,Er3+ and NaYF4:Yb3+,Tm3+).
• Used a single laser to excite both UCNP types concurrently, acquiring their separate luminescence spectra.
• Validated the approach using tandem UCNP pairs and compared results with individual UCNP measurements.

Main Results:

• Successfully demonstrated simultaneous acquisition of spectrally distinct luminescence from two different UCNP types.
• Achieved excellent agreement between tandem UCNP pair measurements and individual UCNP measurements.
• Resolved a temperature difference of ~19 K between two UCNPs separated by ~108 nm, despite overlapping diffraction-limited emission spots.

Conclusions:

• This method enables multi-point temperature gradient mapping within sub-diffraction regions.
• The technique is valuable for applications requiring localized temperature measurements without obstructing the sample surface, such as in catalysis.