Nonergodicity in long-term spectral dynamics of single dye molecules in the low-temperature polymer and organic glass

Abstract

Modern laser spectroscopy brings the advantage of direct experimental study of system ergodicity by comparative analysis of long-term spectral evolution of single molecules (SM) and their ensembles. Here we investigate the experimental spectral trails (measured in Naumov et al 2007 Phys. Rev. Lett. 98 145501) of two SMs which exhibit qualitatively different dynamics: one in a polymer and second in a glassy matrix at T = 4.5 K. For both SMs we have analysed the distributions of the 1st and 2nd cumulants of the fluorescence excitation spectra measured at different time points. It was found that these distributions differ to a variable degree from the corresponding distributions measured for an ensemble of SMs. We treat this result as ergodicity breaking in the systems under study within the considered time scale of hours. It means that the behaviour of time-averaged individual spectral parameters can differ from the ensemble parameters and requires a careful interpretation.