Long-time spectral diffusion induced by short-time energy transfer in doped glasses: Concentration-, wavelength- and temperature dependence of spectral holes

We discovered a remarkable effect: spectral diffusion (SD) induced by energy transfer (ET), here called ET → SD. The 'effective' homogeneous linewidth Γ^′_hom of the S₁ ← S₀ 0-0 band of free-base chlorin (H₂Ch) in polystyrene (PS) was followed as a function of concentration and excitation wavelength by hole-burning. The results cannot simply be explained by Förster's ET mechanism: (1) the increase of Γ^′_hom towards the blue is larger than expected and follows an S-shaped curve; (2) Γ^′_hom increases linearly with concentration; and (3) the holes are Lorentzian. A model is proposed which predicts that Γ^′_hom should increase with delay time, even at T → 0. This is confirmed by experiments.