Spectral hole burning in doped organic crystals and polymer glasses under hydrostatic pressure

We give an overview of results obtained in our isobaric studies of spectral holes in, chlorin-doped glassy polystyrene, frozen n-octane and crystallin e p-terphenyl under various fixed pressures up to 8.4 kbar at 4.2-18 K. Som e results on low-pressure (<0.1 kbar) tuning of spectral holes at 1.5-4.2 K in benzoophenone, biphenyl and frozen n-octane doped with chlorin and in f rozen n-hexane doped with dimethyl-s-tetrazine are also described along wit h a theoretical work on the pressure effects in such nonisobaric studies. T he most interesting effect, observed in our high-pressure isobaric experime nts and explained theoretically, is the pressure-induced narrowing of spect ral holes in glassy polystyrene, caused mainly by reduction in the number o f soft localized modes in a glass under pressure.