The authors demonstrate amplified spontaneous emission (ASE) from quaterthiophene single crystals and study its behavior at low temperature. The room temperature photoluminescence exhibits line narrowing (spectral width down to 10 nm) at 553 nm for excitation fluence larger than 1 mJ cm~(-2). At low temperature (10 K), ASE is observed from two vibronic transitions at 510 nm (0-1) and 553 nm (0-2), with line narrowing down to 5 A, for fluences larger than 100 μJ cm~(-2). The stimulated emission cross section is of the order of 10~(-15) cm~2, and the ASE is found to be strongly affected by thermally induced dynamic disorder. The emission stability under photopumping is also studied and discussed.
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