Water sensitized and highly bright multicolor Ni-doped carbon dots nanoarchitectonics in polar solvents towards stable flexible films

Abstract

To address the issues of low photoluminescence quantum yields (PLQYs), broad PL spectra, and poor stability, multicolor carbon dots (CDs) were synthesized by using different precursors. Blue-emitting CDs were created via a solvothermal synthesis by using citric acid and ethylenediamine while green-emitting CDs were fabricated using O-phenylenediamine. Ni doping further increased the PLQYs and stability of CDs. Ni-doped CDs (Ni-CDs) with blue- and green-emitting were synthesized through a one-step solvothermal method. The PL peak wavelengths of Ni-doped blue CDs (Ni-BCDs) and Ni-doped green CDs (Ni-GCDs) were located at 450 and 540 nm, respectively. After Ni-doping, the average particle size of green-emitting CDs was increased from 2.35 to 2.65 nm. Compared with undoped CDs, Ni-CDs exhibited narrow PL spectra, high PLQYs, and long fluorescent lifetime. The PLQYs of Ni-BCDs and Ni-GCDs were increased to 83.92 and 35.60 %, respectively. Interestingly, the PL peak wavelengths of Ni-doped CDs revealed a red-shift with increasing the solvent polarity (e.g. acetone, acetonitrile, N, N-dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, ethanol, methanol, and H2O). In addition, the PL peaks of green-emitting Ni-CDs generated a large red-shift with increase the ratio of water in organic solvents compared with blue one. Namely, solid Ni-GCDs powders also revealed water dependent PL. After incorporating the CDs in flexible films, Ni-GCDs still revealed high brightness and stability. These results supplied important possibility for the application of multicolor CDs.