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The photon echo (PE) spectroscopy and single‐molecule spectroscopy (SMS) may be combined to give a very powerful tool for comprehensive study of low‐temperature dynamics in dye‐doped disordered solids (polymers, glasses). At the same time, this type of studies are likely to reveal discrepancies when comparing characteristic times of optical dephasing T2 and single‐molecule zero‐phonon spectral lines (ZPL) broadening obtained from PE and SMS, correspondingly, for tetra‐tert‐butylterrylene in polyisobutylene in the temperature range of a few–dozen of Kelvins [see Phys. Status Solidi B 241, 3480 and 3487 (2004)]. Inexplicably, PE‐experiments demonstrated T2‐times to be much shorter than it is sufficient to cause the corresponding ZPL broadening. Here we experimentally solve this problem and show that at T = 4.5–15 K the incoherent PE gives T2‐times which correspond to the narrowest SM ZPL. On the SM‐level there is a pronounced additional ZPL‐broadening due to spectral diffusion processes which are strongly dependent on the characteristics time of the measurement (tens of nanoseconds for PE and seconds for SMS). There is also a broad distribution of ZPL spectral widths for different SMs due to different local environments, that contribute differently to both the optical dephasing and the spectral diffusion processes, but always in addition to the value of inverse optical dephasing times measured using a PE technique.

Luminescence imaging has been adapted to facilitate alignment and focusing of multiple non-collinear laser beams in pump–probe experiments. The technique has been validated in an experiment on four-wave mixing in a doped polymer placed into a high-pressure sapphire-anvil cell, itself inside an optical cryostat.

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