Quantum beats in the phosphorescence of a photo-excited triplet state

Abstract

We have observed quantum beats in the phosphorescence of tetramethylpyrazine-d ₁₂ in a durene host crystal where the two upper spin components (т_z, т_y) decay via a common radiative channel. The initial phase coherence required to make the beats observable was created by a 1/2π microwave pulse resonant with the т_z-т_y transition at 857 MHz. When, after a few microseconds, the phase coherence is lost it can be restored by a second microwave pulse and the beats then appear as an echo signal: from this experiment one obtains a dephasing time T ₂=1·2 μs.