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Raman heterodyne spectroscopy is a powerful tool for characterizing the energy and dynamics of spins. The technique uses an optical pump to transfer coherence from a spin transition to an optical transition where the coherent emission is more easily detected. Here Raman heterodyne spectroscopy is used to probe an isotopically purified ensemble of erbium dopants in a yttrium orthosilicate (Y 2 SiO 5 ) crystal coupled to a microwave cavity. Because the erbium electron spin transition is strongly coupled to the microwave cavity, we observed Raman heterodyne signals at the resonant frequencies of the hybrid spin-cavity modes (polaritons) rather than the bare erbium spin-transition frequency. Using the coupled system, we made saturation recovery measurements of the ground-state spin relaxation time T 1 = 10 ± 3 s and also observed Raman heterodyne signals using an excited state spin transition. We discuss the implications of these results for efforts toward converting microwave quantum states to optical quantum states.

The luminescence from europium doped lanthanum trifluoride (Eu 3þ :LaF 3 ) nano-crystals can be greatly enhanced by capping with b-diketonate organic ligands. Here, we report on photo-stability measurements for the case of nano-crystals capped with thenoyltrifluroacetone (TTA) and compared with those capped with an inactive ligand, oleic acid. With exposure to UV pump light, we observed significant decrease in fluorescence and change in emission spectrum of the TTA-capped nano-particles whilst the fluorescence lifetime remained approximately constant. After a dose of order 70 kJ cm À2 , the luminescence level was similar to that of oleic acid capped nano-crystals. We discuss possible mechanisms. V C 2014 AIP Publishing LLC. [http://dx.