Design and development of electroluminescent white light emitting diodes using carbon dots as active emitters*

Energy conservation has become a major concern globally in today's world and artificial lighting constitutes around ~50% of total energy consumption.Recent advancement in the fabrication of artificial lighting sources include use of semi-conductor quantum dots as active emitters in white light emitting diodes (WLEDs). Semiconductor quantum dots as phosphor material for WLEDs exhibit size-tuneable emissions, high photoluminescence quantum yields, low scattering compared to traditional phosphors. So far quantum dot WLEDs with red green emitting CdSe QDs, CdSe-ZnS QDs, CdS QDs, etc., as phosphor material have been reported in literature. Although WLEDs are fabricated using these dots, they are potentially toxic to be used for indoor and outdoor lighting as they contain highly toxic materials during their fabrication. Further these dots show self-absorption phenomena due to the use of red and green dots in their device structures, affecting the CRI and efficiency of the fabricated device. Henceforth it is ideal to fabricate phosphor using non-toxic materials showing zero self-absorption, high CRIs, high device efficiencies.  The emerging carbon dots seems to be an alternative to semiconductor dots for WLEDs due to their wide availability and broad emissive behaviour with least toxicity increasing their potential applications in fabricating white light emitting devices. Moreover, CDs are resistant to photobleaching and photo blinking, show higher luminescence, and large two photon cross section areas, which makes them highly beneficial for applications in fabricating LED sources. Also, photoluminescence properties of carbon dots can be controlled by modifying the size and surface of carbon dots fabricated. This surface modification of CDs enhances the intensity of PL emission from CDs which can have a direct impact on increasing efficiency of WLED fabricated. In this work we report fabrication of WLEDs with carbon dots as active emitters.