Full-color emission and temperature dependence of the luminescence in poly-P-phenylene ethynylene-ZnS/Mn₂₊ composite particles

The synthesis of a nanocomposite material composed of anionic poly(phenylene ethynylene) (aPPE) polymer particles and ZnS/Mn²⁺ nanoparticles is described, and its luminescence properties are investigated. aPPE particles have two emissions, one in the blue (460 nm) and the other in the green (490 nm), that are assigned to the 0-0 transition and an excimer, respectively. ZnS/Mn²⁺ nanoparticles have an emission at 596 nm that is due to the ⁴T₁-⁶A₁ transition of Mn²⁺ and an emission at 706 nm that is ascribed to defect-related luminescence. The blue, green, yellow, and red emissions make the composite a potential material for full-color displays. More interestingly, the relative intensities of the different emissions may be varied by changing the excitation energy. Infrared spectra reveal that interactions exist between the two particles; however, photoluminescence excitation and emission spectra as well as observations of luminescence lifetimes indicate that there is negligible energy transfer from the polymer particles to the ZnS/Mn²⁺ nanoparticles. Temperature studies reveal that the ZnS/Mn²⁺ particles in the nanocomposite have a significantly reduced thermal quenching energy relative to that of bare ZnS/Mn²⁺ nanoparticles. In addition, between room temperature and 90 °C, the luminescence of the ZnS/Mn²⁺ nanoparticles at 596 nm increases in intensity with increasing temperature. This surprising phenomenon is attributed to thermoluminescence and thermal curing of the particle surface upon heating.