Abstract
Optically detected two‐pulse and three‐pulse echo experiments have been performed under pressure to 50 kbar using a diamond anvil cell. In this paper we report the results on excited triplet neat biacetyl (BA) and BA‐d6. Three‐pulse echoes are easier to perform, and coherence has been maintained for durations longer than one triplet lifetime. In contrast, the two‐pulse echo technique is prone to have spurious contributions, and it is besieged by the envelope modulation effect for BA‐d6. Our data point to the importance of spectral diffusion caused by the bulk nuclei. Their flip–flop motion creates a fluctuating magnetic field on the triplet spin, destroying its coherence. As pressure increases, an increase in number density of such nuclei shortens the phase memory time (TM). A plot of TM vs relative volume produces a linear correlation. Our three‐pulse echo lifetime shows a 40% increase from BA‐h6 to BA‐d6. This very small deuteration effect might suggest that electronic flip–flop, rather than nuclear spin flip–flop, is the dominant relaxing mode. However, a study of TM on different exciting light levels disproves this mechanism