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

A new effect in doped organic glasses, which we refer to as "energy transfe r (ET)-induced spectral diffusion (SD)," ET-->SD, has recently been reporte d by us. In this process ''extra'' SD, in addition to "normal" SD in glasse s, is triggered by the energy balance released on "downhill" ET. Quantitati ve aspects of the ET-->SD process have been investigated by means of time-r esolved hole-burning experiments on free-base chlorin (H(2)Ch) in polystyre ne (PS) presented here. The "effective" homogeneous linewidth r(hom)' was d etermined as a function of delay time t(d) (10(-5) - 10(3) s), temperature (1.2 to 4.2 K) and concentration (c = 1 x 10(-5) to 6 x 10(3) M), at variou s excitation wavelengths within the S-1 <-- S-0 0-0 band. Gamma(hom)' as a function of temperature was found to obey the relation Gamma(hom)' = Gamma( 0)' + aT(1.3), characteristic for glasses, and we present an analysis of th e residual Linewidth Gamma(0)' and the coupling constant a. In this analysi s we determined (i) the separate contributions to Gamma(0)' arising from th e fluorescence lifetime, ET, and ET-->SD, (ii) the separate contributions t o a arising from "pure" dephasing, "normal" SD, and "extra" spectral diffus ion caused by ET-->SD. The contributions of ET-->SD to Gamma(0)' and a prov e to be proportional to the concentration and to the logarithm of the delay time (proportional to c log t(d)). (C) 1999 American Institute of Physics. [S0021-9606(99)53001-8].