We demonstrate optical amplification over a band >850 meV, via simultaneous exploitation of stimulated emission from mixed polymer systems in which energy transfer from the higher to lower-gap material is inhibited thanks to a complex interplay between morphology and interchain decoupling, driven by chain encapsulation. Amplified spontaneous emission (ASE) is obtained both with ad-hoc pumping into the relevant bands or with a single excitation (400 nm) able to sustain ASE at both wavelengths simultaneously (two-colour ASE).