Laser Refrigeration by an Ytterbium‐Doped NaYF₄ Microspinner

Abstract

Thermal control of liquids with high (micrometric) spatial resolution is required for advanced research such as single molecule/cell studies (where temperature is a key factor) or for the development of advanced microfluidic devices (based on the creation of thermal gradients at the microscale). Local and remote heating of liquids is easily achieved by focusing a laser beam with wavelength adjusted to absorption bands of the liquid medium or of the embedded colloidal absorbers. The opposite effect, that is highly localized cooling, is much more difficult to achieve. It requires the use of a refrigerating micro‐/nanoparticle which should overcome the intrinsic liquid heating. Remote monitoring of such localized cooling, typically of a few degrees, is even more challenging. In this work, a solution to both problems is provided. Remote cooling in D2O is achieved via anti‐Stokes emission by using an optically driven ytterbium‐doped NaYF4 microparticle. Simultaneously, the magnitude of cooling is determined by mechanical thermometry based on the analysis of the spinning dynamics of the same NaYF4 microparticle. The angular deceleration of the NaYF4 particle, caused by the cooling‐induced increase of medium viscosity, reveals liquid refrigeration by over −6 K below ambient conditions.

Understanding and Preventing Photoluminescence Quenching to Achieve Unity Photoluminescence Quantum Yield in Yb:YLF Nanocrystals

“…(influenced by the number of phonons present, Supporting Information SI-18 and SI-19), but the results do not yet convincingly show evidence of cooling, possibly as a result of too efficient heat transfer from the surroundings to the NCs. Efforts to measure optical refrigeration on single NCs using optical levitation, as reported before, ,− are currently under way.…”

Inert Shell Coating for Enhanced Laser Refrigeration of Nanoparticles: Application in Levitated Optomechanics

“…It took several years to improve the quality of the crystals grown by the moisture-free bulk Czochraski method to laser-cool a 10% Yb 3+ :LiYF 4 bulk crystal down to an impressive record low temperature of 91 K from room temperature . The laser refrigeration of another host material, NaYF, was demonstrated first in reference 24 and later in reference 25 using Yb 3+ -doped β-phase NaYF optically trapped in an aqueous medium. Contrary to LiYF 4 (lithium–yttrium–fluoride), the stoichiometry of sodium–yttrium–fluoride materials is complex and can vary depending on the synthesis, , hence our use of the notation NaYF to describe this material.…”

Phonon‐Assisted Negative Thermal Quenching in a One‐Photon Up‐Conversion Phosphor for Thermometry

“…[1] While the energy of the emission is greater than DOI: 10.1002/lpor.202300499 that of excitation, it is determined to be an anti-Stokes emission (Figure 1b). [2] This unique anti-Stokes emission has drawn considerable interest for its promising technological applications in photovoltaics, [3] photocatalysis, [4] bioimaging, [5] laser, [6] optical refrigeration, [7] and so on. Nevertheless, both the Stokes and anti-Stokes emission of the involved phosphors is generally affected by ambient temperature, [8] which usually quenches at elevated temperature, causing decreased efficiency of the corresponding phosphor.…”