SPECTRAL DIFFUSION IN ORGANIC GLASSES - TEMPERATURE-DEPENDENCE OF PERMANENT AND TRANSIENT HOLES

Spectral diffusion of the S1<--S0 0-0 transition (Q(y)) of bacteriochlorophyll a (BChl a) as guest in the glasses ethanol (EtOH), triethylamine (TEA), 2-methyltetrahydrofuran (MTHF) and diethylether at low temperature has been studied by transient and permanent hole burning with a single-mode GaAlAs diode laser at almost-equal-to 780 nm. Transient holes decay on about 100 ms, determined by the triplet-state lifetime of BChl a. Their widths are compared to those of permanent holes probed on a time scale of minutes; both follow a T1.3+/-0.1 temperature dependence between 1.2 and 42 K and extrapolate to the fluorescence life-time-limited value for T-->0. The amount of spectral diffusion, derived from the difference in width of permanent and transient holes over a time span between almost-equal-to 10(-5) and almost-equal-to 10(2) s, strongly depends on the glassy host.