Laser refrigeration of rare-earth doped sodium-yttrium-fluoride nanowires

Abstract

Hexagonal sodium yttrium fluoride (β-NaYF 4 ) crystals are currently being studied for a wide range of applications including color displays, solar cells, photocatalysis, and bio-imagβing. β-NaYF 4 has also been predicted to be a promising host material for laser refrigeration of solids. However, due to challenges with growing Czochralski β- NaYF 4 single-crystals, laser refrigeration of bulk β-NaYF 4 has not yet been achieved6. Recently hydrothermal processing has been reported to produce Yb-doped β-NaYF 4 nanowires (NWs) that undergo laser refrigeration during single-beam optical trapping experiments in heavy water. The local refrigeration of the individual nanowire is quantified through the analysis of its Brownian motion through the analysis of forward scattered light that is focused onto a quadrant photodiode. The individual β-NaYF 4 nanowires show maximum local cooling of 9°C below ambient conditions. Here we present the emission lifetime for the 4 S 3/2 – 4 I 15/2 transition for Er(III) ions in Yb/Er-codoped -NaYF 4 NW ensembles was measured to be (220 ± 6) μs using a an electron multiplying charge coupled device (EMCCD) as a detector with high spatial resolution. This lifetime is consistent with values reported in the literature.