The composite CdSe/ZnS core – shell mixed with pyrene molecules in polymethyl methacrylate (PMMA) polymer was used to generate intense white light when illuminated by InGaN/GaN UV LED. The addition of pyrene molecules in low concentration to the core – shell system tuned the chromaticity coordinates to (0.25, 0.34) and increased the intensity of the emitted white light. This improvement was attributed to the overlap of pyrene excimer emission with the absorption spectrum of CdSe/ZnS core – shell which leads to a cold white light generation. The synthesis of core – shell nanoparticles, with the pyrene molecules in PMMA films, is presented. The photoluminescence spectra of the pyrene, CdSe/ZnS core – shell and their mixture composite in PMMA were tested. The Gaussian fit was used to determine the chromaticity coordinate of the emitted white light.