Abstract

The absorption and luminescence spectra of α-perylene crystals have been measured under pressure in the range from ambient pressure (0 kbar) to 40 kbar. At 77 K, the free-exciton luminescence band shifts toward lower energy with pressure, at a rate of −58 cm −1/kbar, while the luminescence band arising from self-trapped excitons shifts toward higher energy at a rate of +55 cm −1/kbar, which is indicative of the instability of self-trapped excitons. The change in the exciton—phonon coupling strength from a strong- ( g > 1) to weak-coupling ( g < 1) regime occurs at about 6 kbar. At both room and liquid-nitrogen temperatures, the Y state turns out to be the most stable state at high pressure.

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