The peak of the luminescence spectrum of zinc oxide (ZnO) is usually observed above 500 nm (yellow region). By in-situ growth of ZnO nanoparticles in a poly(ethylene glycol) (PEG) matrix, we have succeeded in producing ZnO/polymer composites with stable luminescence peaks down to 465 nm (blue region). The unbalanced precursor molarity approach, where the molarity of one precursor (LiOH) is several times larger than the molarity represented by a chemical reaction balance, was used. The blue luminescence, which was accompanied by an enhancement of luminescence intensity, was observed at very high LiOH concentrations. This was probably due to the simultaneous reduction in the crystalline size and improvement in the crystallinity. Doping ZnO nanoparticles with europium also generated a red luminescence at 616 nm, due to the 5D0 →7F2 transition of Eu ions.