Massive enhancement of persistent spectral hole-burning in the R-lines of NaMgAl(oxalate)3 · 9H2O:Cr(III) by partial deuteration

Partial deuteration of NaMgAl(oxalate)3 · 9H2O:Cr(III) (0.5%) increases the quantum efficiency for persistent spectral hole-burning in the R1-line by three orders of magnitude. A 50% deuterated crystal shows an impressive initial hole-burning efficiency of ≈0.1% and sharp anti-holes are observed in the range of ±15 GHz. A decrease of the quantum efficiency upon deuteration has often been reported in the literature and this has been rationalized on the basis of the lower tunnelling probability of the deuteron in the double well potential of hydrogen bonds. In contrast, the present findings of a sensational increase can be rationalized by a hole-burning mechanism based on 180° flip motions of the lattice water molecules around their pseudo C2 axes. Considering the spin-flip nature of the electronic excitation this is an extraordinary finding. The deuteration effect may be used to design high-efficiency hole-burning materials for optical storage at liquid nitrogen temperatures.