Microwave-Assisted Polyol Synthesis of Water Dispersible Red-Emitting Eu3+-Modified Carbon Dots

Abstract

Eu3+-modified carbon dots (C-dots), 3–5 nm in diameter, were prepared, functionalized, and stabilized via a one-pot polyol synthesis. The role of Eu2+/Eu3+, the influence of O2 (oxidation) and H2O (hydrolysis), as well as the impact of the heating procedure (conventional resistance heating and microwave (MW) heating) were explored. With the reducing conditions of the polyol at the elevated temperature of synthesis (200–230 °C), first of all, Eu2+ was obtained resulting in the blue emission of the C-dots. Subsequent to O2-driven oxidation, Eu3+-modified, red-emitting C-dots were realized. However, the Eu3+ emission is rapidly quenched by water for C-dots prepared via conventional resistance heating. In contrast to the hydroxyl functionalization of conventionally-heated C-dots, MW-heating results in a carboxylate functionalization of the C-dots. Carboxylate-coordinated Eu3+, however, turned out as highly stable even in water. Based on this fundamental understanding of synthesis and material, in sum, a one-pot polyol approach is established that results in H2O-dispersable C-dots with intense red Eu3+-line-type emission.

Polyol-Mediated Synthesis of Nitrogen-Containing Carbon-Dots from Tetracyanobenzene with Intense Red Fluorescence

“…Lifetime measurements for the emission at 715 nm for both types of excitation ( λ exc = 454 nm and λ exc = 633 nm) result in a decay of 1.4 to 4.3 ns ( τ 1 = 1.8, τ 2 = 4.4 ns for λ exc = 454 nm; τ 1 = 1.4, τ 2 = 3.6 ns for λ exc = 633 nm) (Figure 7). These values are in good agreement with previously reported lifetime data of C-dots ( τ ~ 1–10 ns) [35,36,37]. Finally, it needs to be noticed that the emission of C-dots made from TCB is significantly different from the emission of pure TCB (Figure 6b).…”

Recent Advances in Synthesis, Modification, Characterization, and Applications of Carbon Dots

“…Iron-doped CDs were synthesized by introducing iron benzoate [ 69 ], FeCl 3 [ 70 ], or Fe-gluconate [ 71 ] as precursors. Moreover, other metal-doped CQDs have also been synthesized and applied for different applications, such as manganese-doped CDs [ 72 ], Zn-doped CDs [ 73 ], cobalt(II)-doped CDs [ 74 ], gadolinium-doped CDs [ 75 ], europium-doped CDs [ 76 ], Ce doped-CDs [ 77 ], terbium-doped CDs [ 78 ], europium-doped CDs [ 79 ], ruthenium-doped CDs [ 80 ], and germanium-doped CDs [ 81 ].…”

Synthesis and Applications of Red‐Emissive Carbon Dots

“…And the products can be obtained within a few minutes, with an improved yield. For example, Feldmann and coauthors obtained the Eu 3+ ‐modified CDs with a diameter of 3–5 nm via a one‐pot polyol synthesis . In brief, 0.2 mmol of EuCl 3 ⋅ 6H 2 O were dissolved in 50 mL of PEG400, which was heated via a microwave oven in a round‐bottomed flask to 200 °C in an argon atmosphere.…”

“…Ultimately, yellowish powders were collected after centrifugation and can be redispersible in water. Most importantly, the photoluminescence wavelength of Eu‐modified C‐dots can be adjusted by the oxygen treatment with time, from 440 to 614 nm, when excited at 366 nm, which has many potential applications in biological imaging or clinical areas …”