Recently π-conjugated semiconductor polymers have been proposed as laser-active media. In order to achieve lasing, it is essential to observe optical gain in these materials. By using nanosecond pulses from a Q-switched Nd:YAG laser and the variable stripe length (VSL) method the steady-state photoluminescence (PL) spectra was measured for various soluble alkoxy derivatives of poly(para-phenylenevinylene) neat films. The PL emission is red-shifted from the ab- sorption and shows an exponential growth characteristic of a net gain coefficient. The results show evidence of stimulated emission (SE) which is largely due to intrachain singlet exciton recombination processes and its spectral shift is sidegroup dependent. The VSL method resolves the optical gain spectra as well as its shape in the visible spectral range.
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