White-light emission results from the superposition of green, red, and blue light. Low-cost, high-efficiency white-light emitting organic materials are highly attractive for various lighting sources, including flexible full-color displays and backlights. However, manufacturing these materials remains a challenge for both materials chemists and device physicists alike.

Fig. 1: Schematic illustration of a white-light emitting film composed of micelles containing red and green fluorescent dyes surrounded by a blue-light emitting polymer.

Now, Juan Peng from Fudan University in Shanghai and colleagues1 have designed a simple white-light emitting organic system using polymer-based films incorporating blue-, green-, and red-light emitting fluorescent dyes (Fig. 1).

In their system design, they introduced red- and green-light emitting organic dyes inside different nanosized phase-separated polymer aggregates known as micelles, which they mixed with a blue-emitting polymer to form a single layer. The simultaneous emission from the three dyes resulted in white-light emission.

“Our method of loading fluorescent dyes in the core of micelles is a simpler, cost-effective strategy to achieve white-light emission,” says Peng.

The researchers simply stirred the fluorescent dyes into separate micelle solutions in toluene for three days to load them into the micelles. Because the dyes were insoluble in toluene, the formation of homogenous fluorescent solutions indicated that the dyes were effectively incorporated into the micelle cores. Emission spectroscopy showed that the dyes retained their optical properties inside the micelles.

When two different dyes were loaded in the same micelle, fluorescence resonance energy transfer occurred between the dyes. However, when the dyes were loaded in separate micelles, the energy transfer was suppressed, allowing the dyes to emit simultaneously. Adjusting the relative ratios between the fluorescent species allowed the color components of the emitted light to be tuned.

“The fluorescence resonance energy transfer between dyes is inhibited due to isolation of the micelles,” says Peng. The researchers chose polyfluorene as the blue-emitting polymer and, unlike the red and green dyes, they mixed it with the pre-loaded micelles because of its large size and its low affinity with the micelle cores.

“Polyfluorene facilitates the fabrication of a homogenous film instead of a film with micelles and holes,” says Peng.

Polyfluorene is also a semiconducting polymer that may find applications in the design of optoelectronic devices. The team is currently studying the fabrication of white-light emitting diodes.