Gram‐Scale Synthesis of Highly Efficient Rare‐Earth‐Element‐Free Red/Green/Blue Solid‐State Bandgap Fluorescent Carbon Quantum Rings for White Light‐Emitting Diodes

Abstract

The negative impact of rare-earth elements (REEs) on the environment, limited supply and high cost prompt the need for REE-free phosphor-converted white light-emitting diodes (LEDs). Here, we report the gram-scale synthesis of red/green/blue solid-state bandgap fluorescent carbon quantum rings (R/G/B-SBF-CQRs) with high quantum yields up to 30-46 %. This was achieved using cyano-group-bearing pphenyldiacetonitrile as precursor and forming carbon quantum rings of different diameters through the linkage of curved carbon quantum ribbons of different lengths. The results show the role of cyano groups in inducing the curvature of the carbon quantum ribbons for CQR formation and emission of stable solid-state bandgap fluorescence. R/G/B-SBF-CQRsphosphor-based LEDs emitted warm white light with low CCT (3576 K), high CRI (96.6), and high luminous efficiency (48.7 lm W À1 ), comparable to REE-phosphor-based LEDs.

High-quality full-color carbon quantum dots synthesized under an unprecedentedly mild condition

“…Moreover, the average mass yield of the CQDs reached 69.0% ( Table S1 ), which was comparable to previous work ( Meng et al., 2021 ). The absolute photoluminescent quantum yield for d-bCQDs, m -bCQDs, o -gCQDs, and p -rCQDs was determined to be 35.3%, 0.6%, 16%, and 7.9% ( Figure S7 ).…”

“…By mixing the solutions of d-bCQDs, o -gCQDs, and p -rCQDs at different volume ratios, various photoluminescent colors including blue, cyan, green, orange, red, and even white were created ( Figures 4 A and S24 ). The QY reached 19.2% for the white CQDs from this facile strategy, which is comparable to most of the reported CQDs that depended on other harsh preparation methods ( Wang et al., 2020 ; Ding et al., 2016 ; Qin et al., 2019 ; Meng et al., 2021 ; Liu et al., 2012 ; Yuan et al., 2018 ). To further obtain solid-state CQDs, an electrostatic deposition method was used to deposit the CQDs on positively charged SiO 2 microparticles (modified with APTES), as the CQDs exhibited negative Zeta potentials that were attributed to the excessive carboxyl groups ( Figures S16 and 4 B).…”

“…BTCA was selected as the acidic reagent, and mPDA, oPDA, and pPDA were chosen as the basic reagents. The reactions were performed by heating the mixture of BTCA and one of the selected bases in N,N-dimethylformamide (DMF) in glass bottles under 85°C for only 6 h, which was far below the temperatures in hydrothermal and solvothermal reactions ( Wang et al., 2017 , 2020 ; Ding et al., 2016 ; Qin et al., 2019 ; Meng et al., 2021 ; Liu et al., 2012 ; Yuan et al., 2018 ). Three CQDs that presented bright blue, green, and red light emission bands centered at about 440, 550, and 605 nm, respectively, were obtained ( Figures 2 A–2C).…”

“…As far as we know, full-color CQDs were scarcely prepared under 100°C by using any other “bottom-up” methods ( Figure 2 E) ( Wang et al., 2020 ; Ding et al., 2016 ; Qin et al., 2019 ; Meng et al., 2021 ; Liu et al., 2012 ; Yuan et al., 2018 ). The temperature was even far below the boiling point of the solvent, which left the pressure estimated to be 1.88 bar (text S1.3).…”

Preparation of Multicolour Solid Fluorescent Carbon Dots for Light-Emitting Diodes Using Phenylethylamine as a Co-Carbonization Agent

“…The CDs were used in LEDs due to their unique optical properties, excellent colour stability and wide emission peaks ( Figure S2 ). The three kinds of CDs were directly coated on UV-LED chips to obtain orange, green and blue LEDs ( Figure 8 a–c) [ 48 , 49 , 50 , 51 ]. Their optimal fluorescence centres are at 589, 535 and 457 nm, consistent with the solid fluorescence results of the original CDs.…”