Carbon quantum dots (CQDs) have emerged as promising materials for optoelectronic applications on account of carbon’s intrinsic merits of high stability, low cost, and environment-friendliness. However, the CQDs usually give broad emission with full width at half maximum exceeding 80 nm, which fundamentally limit their display applications. Here we demonstrate multicolored narrow bandwidth emission (full width at half maximum of 30 nm) from triangular CQDs with a quantum yield up to 54–72%. Detailed structural and optical characterizations together with theoretical calculations reveal that the molecular purity and crystalline perfection of the triangular CQDs are key to the high color-purity. Moreover, multicolored light-emitting diodes based on these CQDs display good stability, high color-purity, and high-performance with maximum luminance of 1882–4762 cd m−2 and current efficiency of 1.22–5.11 cd A−1. This work will set the stage for developing next-generation high-performance CQDs-based light-emitting diodes.

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colloidal semiconductor quantum dots (QDs) especially the Cd 2+ -based QDs such as CdSe and CdTe emerged as good candidates for the development of random lasers since their unique and attractive optical characteristics, such as high quantum yield (QY), small Stokes shifts, and narrow emission bandwidths, can facilitate the ultrafast build-up of population inversion and the subsequent optical amplification at a low pump energy density. [4][5][6] Considerable efforts have been invested and remarkable progress has been made on the design and fabrication of highly efficient random lasers with high spectral purities based on the perovskites and Cd 2+ -based QDs in simple device configurations. [7][8][9][10] However, the intrinsic instability as well as the severe toxicity are still significant impediments to deploying perovskites and Cd 2+ -based QDs as next-generation light-emitting materials for future ultrastable and low-threshold random lasing applications. [7][8][9][10] The bandgap emission carbon quantum dots (BE-CQDs) have recently emerged as a promising alternative to perovskites and traditional semiconductor QDs for optoelectronic devices, such as solution-processed electroluminescent light-emitting diodes (LEDs) [11][12][13] and lasers, by taking advantage of carbon's intrinsic merits of high stability, low cost, high abundance, and environment friendliness. [14][15][16][17][18][19][20][21] In our recent work, for the first time, we have realized full-color random lasing with lasing thresholds in the range of 2.1-5.8 mJ cm −2 in blue, green, red, and white colors based on bright multicolor fluorescent BE-CQDs. [14] The random lasers show much better operating stability than those of perovskites and Cd 2+ -based QDs, laying a solid foundation for developing the next-generation laser technology. [7][8][9][10][22][23][24] However, the large Stokes shifts (>80 nm) and the large full width at half maximum (FWHM > 80 nm) of the BE-CQDs inevitably result in the dissipation of exciton energy into heat and prevent sustaining population inversion during the pumping process, thus fundamentally limiting the further performance improvement especially on pump thresholds for the random lasing. [14][15][16][17][18][19][20][21] Without a doubt, the best approach to realizing tunable stable CQDs-based random lasers with a much lower pump threshold for lasing is to develop bright multicolor fluorescent CQDs with small Stokes shifts (<20 nm) and small FWHM (<40 nm).Most recently, we have demonstrated the first synthesis of highly efficient narrow bandwidth emission triangular CQDsThe development of ultrastable and low-threshold random lasers has long been the subject of intense academic research, in anticipation for widespread applications spanning from military weapon devices, biomedical therapy, and materials processing to energy savings. Reported here is the first example of ultrastable and low-threshold random lasing emissions ranging from blue to red based on narrow bandwidth emission triangular carbon quantum dots (CQDs)....

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In the version of this article originally published, Figs. 2(d) and 3(a), and Figs. S3 and S6 in the Electronic Supplementary Material (ESM) were incorrect. The corrected images are shown below.