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. 2025 May 2;18(9):2094.
doi: 10.3390/ma18092094.

Effect of Annealing Temperature on the Photoluminescence Blue Shift of Nitrogen-Doped Graphene Quantum Dots

Xiaofen Xu  1   2 , Jun Guo  1 , Lu Han  1 , Huimin Fan  1 , Fei Tong  1
Affiliations

Effect of Annealing Temperature on the Photoluminescence Blue Shift of Nitrogen-Doped Graphene Quantum Dots

Xiaofen Xu et al. Materials (Basel). .

Abstract

Nitrogen-doped graphene quantum dots (NGQDs) are made by heating a mixture of GQDs and ammonia using a thermochemical method. The optical properties of the samples were studied. Here, the role of the temperature used in the annealing process is investigated. It is found that with the increase in heating temperature, the sp2 fraction content continuously increases, and the photoluminescence (PL) blue shift continuously increases. The 550 nm peak of GQDs shifts from 550 nm to 513 nm NGQDs synthesized at 300 °C. The normalized PL intensity shows a significant blue shift in the emission peak of the NGQD samples compared to the GQDs. The peak position of the GQDs is 555 nm, while the peak positions of the NGQDs are 511 nm for NGQDs-250, 488 nm for NGQDs-300, and 480 nm for NGQDs-350. Using a simple thermochemical method, we can effectively dope N into GQDs, and it is evident from the electron energy loss spectra that N doping induces the emergence of a new energy level in the electronic structure, which alters the optical properties of NGQDs.

Keywords: NGQDs; blue shift; mechanism; photoluminescence (PL).

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1
Figure 1
Schematic diagram of the experimental setup.
Figure 2
Figure 2
TEM images of the (a) GQDs and (b) NGQDs-300 (inset: HR-TEM images). The diameter distributions of (c) GQDs and (d) NGQDs-300.
Figure 3
Figure 3
(a) FTIR and (b) Raman spectra of the GQD and NGQD samples.
Figure 4
Figure 4
(a) The survey XPS spectra of GQD and NGQD samples. (b) C1s spectra of NGQDs-300. (c) N1s spectra of NGQDs-300. (d) Nitrogen-related components of the NGQD samples heated at different temperatures.
Figure 5
Figure 5
PL spectra of (a) GQDs and (b) NGQDs-300. (c) Normalized PL spectra of GQD and NGQD samples. (d) The dependence of the PL blue shift of the NGQD samples compared to GQDs on the value of sp2 fraction.
Figure 6
Figure 6
(a) UV-vis absorption spectra of the GQDs and NGQDs. (b) Schematic energy level diagram of NGQDs. Proposed PL emission mechanisms of (c) GQDs and (d) NGQDs.
See this image and copyright information in PMC

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