Relaxation und optische Kernspinpolarisation der Protonen in optisch angeregten Anthracen-Kristallen

Abstract

The influence of optically excited metastable triplet states on the spin lattice relaxation time T₁ of protons in anthracene is investigated at room temperature. From the H₀-field dependence of T₁ in the presence of excited triplets we calculate the hopping time of triplet excitons τ_c=(5±1) · 10^–12 sec. Especially in the low field region a new type of dynamic nuclear polarisation is observed. Triplet excitons, which are excited using unpolarized light produce via optical exciton spin polarisation an optical nuclear spin polarisation. Polarisation factors of more than 1000 are observed. Preliminary experiments with anthracene-tetracene mixed crystals are able to separate relaxation and polarisation effects due to mobile excitons from effects, which don’t need the mobility of excitons.