Blue‐Emitting Boron‐ and Nitrogen‐Doped Carbon Dots for White Light‐Emitting Electrochemical Cells

This work describes the first use of blue-emitting boron- and nitrogen-doped carbon dots (BN-CDs), rationalizing their photoluminescence behavior in solution and ion-based thin-films to prepare white light-emitting electrochemical cells (LECs). In detail, a cost-effective and scalable water-based microwave-assisted synthesis procedure is set for BN-CDs featuring an amorphous carbon-core doped with N and B. While they show a bright (photoluminescence quantum yield of 42%) and excitation-independent blue-emission (440 nm) in solution related to emitting n−π* surface states, they are not emissive in thin-films due to aggregation-induced quenching. Upon fine-tuning the film composition (ion-based host), an excitation dependent emission covering the whole visible range is noted caused by interaction of the ion electrolyte with the peripheral functionalization of the BN-CDs. Moreover, the efficient energy transfer from the host to the BN-CDs emitting species enabled good performing LECs with white emission (x/y CIE coordinates of 0.30/0.35, correlated color temperature of 6795 K, color rendering index of 87) and maximum luminance of 40 cd m−2, and stabilities of a few hours. This represents a significant improvement compared to the prior-art monochromatic CD-based LECs with similar brightness levels, but stabilities of <1 min.