Poly(vinyl alcohol) (PVA)/poly(vinyl acetate) (PVAc) blends in different proportions show phase separation in the solid state. The dimensions, shapes, and distributions of the domains produced by the phase separation process are dependent on the composition and can be observed by conventional optical microscopy. However, using fluorescence optical microscopy of polymer blends in different compositions containing anthracene and/or fluorescein molecules dissolved in the matrices we were able to do a chemical discrimination of each domain. We also observed that anthracene is mainly localized in PVAc domains and fluorescein in PVA domains, and that the diffusion process of these fluorophers within the matrices is controlled by specific polymer-dye interactions.