An efficient and stable fluorescent graphene quantum dot-agar composite as a converting material in white light emitting diodes

Graphene quantum dots (GQDs) have attracted great attention due to their unique optoelectronic properties. There remains a critical challenge to utilize the water-soluble GQDs for device applications. Here we report a facile method to fabricate a GQD-agar composite. The composite exhibits excellent optical stability and no luminescence quenching is observed. The composite is successfully applied as a colour converting material in blue light-emitting diodes (LEDs) to achieve white light emission. The luminous efficiency and light conversion efficiency of the white LED are 42.2 lm W-1 and 61.1% respectively. The light conversion efficiency of the WLED is stable for over 100 hours of continuous operation.