Spectral diffusion induced by energy transfer in doped organic glasses: Delay-time dependence of spectral holes

Abstract

A new effect in doped organic glasses, which we refer to as “energy transfer (ET)-induced spectral diffusion (SD),” ET→SD, has recently been reported by us. In this process “extra” SD, in addition to “normal” SD in glasses, is triggered by the energy balance released on “downhill” ET. Quantitative aspects of the ET→SD process have been investigated by means of time-resolved hole-burning experiments on free-base chlorin (H2Ch) in polystyrene (PS) presented here. The “effective” homogeneous linewidth Γhom′ was determined as a function of delay time td (10−5−103 s), temperature (1.2 to 4.2 K) and concentration (c=1×10−5 to 6×103 M), at various excitation wavelengths within the S1←S0 0-0 band. Γhom′ as a function of temperature was found to obey the relation Γhom′=Γ0′+aT1.3, characteristic for glasses, and we present an analysis of the residual linewidth Γ0′ and the coupling constant a. In this analysis we determined (i) the separate contributions to Γ0′ arising from the fluorescence lifetime, ET, and ET→SD, (ii) the separate contributions to a arising from “pure” dephasing, “normal” SD, and “extra” spectral diffusion caused by ET→SD. The contributions of ET→SD to Γ0′ and a prove to be proportional to the concentration and to the logarithm of the delay time (∝c log td).