Yellow light-emitting polymer bearing fluorescein dye units: Photophysical property and application as luminescence converter of a hybrid LED

Yellow-light emitting polymer particles (spherical shape ∼500-700 nm) were prepared from a solution of polyester bearing fluorescein dye units in tetrahydrofuran, via simple evaporation of the solvent. The morphology of the polymer particles was dependent on the concentration of a base such as triethylamine (TEA), probably due to a change in the balance between interactions among the polymer chains and interactions of the polymer chain with TEA molecules. Thus when a polymer solution containing an appropriate amount of TEA (pH 7.76) was evaporated, the resulting polymer particles became more distinct in the shape and larger in size (∼1-2 μm). A hybrid light-emitting diode (LED) was fabricated, employing the polymer and a blue LED (460 nm) as a luminescence converter and a primary light source, respectively. When the polymer content was 10 wt.% in epoxy, a white emission was observed (1.81 lm at 20 mA).