LPL materials better known as "glow-in-the-dark" pigments, store excitation energy in excited states that slowly release their energy as light.
Today, most LPL materials are based on an inorganic system of strontium aluminium oxide (SrAl 2O4) doped with europium and dysprosium, and exhibit emission for more than ten hours, but such a system requires rare elements and temperatures higher than 1,000ºC during fabrication. What's more, light scattering by SrAl 2O4 powders limits the transparency of LPL paints, the authors note. The researchers designed an organic LPL (OLPL) system consisting of two simple organic molecules, free from rare elements and easy to manufacture, which can emit light for more than one hour at room temperature after being excited by a standard white LED light source.
The material luminesces even at temperatures over 100ºC. It is also transparent and soluble, as well as being potentially flexible and colour-tuneable, which make the researchers hope the new molecules could be used in large-area applications including flexible paints, biomarkers, fabrics, and windows.
By studying the long-lived charge separation in this novel organic system, the authors expect that a wide variety of organic semiconductor devices will also be better understood.
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