Photochemical hole burning of phthalocyanine in polymer glasses: Thermal cycling and spectral diffusion

In this paper we report an analysis of hole burning line shapes yielding both reversible and irreversible contributions to the linewidth which are due to spectral diffusion. These terms show a linear T dependence and can, through cycling experiments, be investigated in the temperature range of 0.5<T<25 K. The range 1<T<25 K is particularly interesting because, under normal conditions, Debye contributions and local mode contributions overwhelm the small spectral diffusion terms at these temperatures. Comparison between optical data and specific heat data supports our model of spectral diffusion.