Spectral diffusion in organic glasses. Temperature dependence of permanent and transient holes

Abstract

Spectral diffusion of the S 1←S 0 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 ≈ 780 nm. Transient holes decay on a time scale of 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 T 1.3±0.1 temperature dependence between 1.2 and 4.2 K and extrapolate to the fluorescence lifetime-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 ≈ 10 −5 and ≈10 2 s, strongly depends on the glassy host.