Memory of low magnetic fields in persistent spectral hole-burning of the 2E←4A2 spin-flip transition in NaMgAl(oxalate)3·9H2O:Cr(III)

The effects of weak magnetic fields (<16 mT) in persistent non-photochemical spectral hole-burning of the R1-line (2E←4A2 transition) in NaMgAl(oxalate)3·9H2O:Cr(III) are reported. The observed hole patterns can be quantitatively rationalized with excited state g-factors, gzex=1.395±0.015, gxex=2.00±0.08, and gyex=1.82±0.08. The deviation from trigonal behavior implies the presence of a significant low symmetry ligand–field. Measuring the hole-burning spectrum in a magnetic field after burning in zero field and vice versa yields the same hole pattern. The latter provides a persistent memory of magnetic fields. Zeeman effects in spectral holes may also be used to stabilize and tune the frequency of single-mode semiconductor lasers.