Condensed-phase Ytterbium Coordination Complexes for Field Sensing

Crystals composed of molecules containing a single rare-earth ion (REI) featuring narrow f-f transitions may be utilized as sensors analogous to atomic vapor cells but with much higher spin density. However, few REI crystals are able to sustain their advantages at temperatures above several kelvins. Our previous work has highlighted the potential application of large Ytterbium-centered molecules in the solution phase for magnetic sensing even at room temperature. Here, we report on advancements in (thiolfan)YbCl(2-MeTHF) and (thiolfan)^*YbCl(2-MeTHF)₂, revealing narrow hole-burning linewidths in the tens of kilohertz at 77 K. Remarkably, these optical absorption spectra remain stable across temperatures from 20 – 90 K. By harnessing the transition’s power and polarization dependence, we demonstrate frequency-selective optical depletion of a spectral subset of electronic spins. The systematic study shows large REI molecules not only increase the densities of manipulable electronic spins on the order of Avogadro’s number (10²³) but also preserve narrow transitions at higher temperatures, offering an alternative approach to pushing the boundaries of gas-phase atomic systems.