Detection of a precursor in a strong first-order structural phase transition by a fluorescence-lifetime measurement

A precursor of the strong first-order structural phase transition in a resorcinol [C₆{H}₆$(OH${)}₂$] crystal was detected by measuring the lifetime of the fluorescence. A critical decrease in the lifetime and an increase in the intensity of the impurity-induced fluorescence were found to occur starting from 30 K below Tc. Large-amplitude and short-lived vibrational fluctuations associated with the phase transition are suggested as a possible origin of the precursor.