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In citric acid-based carbon dots, molecular fluorophore contributes greatly to the fluorescence emission. In this paper, the nitrogen and sulfur co-doped carbon dots (N,S-CDs) were prepared, and an independent sulfur source is selected to achieve the doping controllability. The influence of sulfur doping on the molecular fluorophore was systematically studied. The introduction of sulfur atoms may promote the formation of molecular fluorophore due to the increased nitrogen content in CDs. The addition surface states containing sulfur were produced, and S element exists as –SO3, and –SO4 groups. Appreciate ratio of nitrogen and sulfur sources can improve the fluorescence emission. The photoluminescence quantum yields (PLQY) is increased from 56.4% of the single N-doping CDs to 63.4% of double-doping CDs, which ascribes to the synergistic effect of molecular fluorophores and surface states. The sensitivity of fluorescence to pH response and various metal ions was also explored.

Evaluating the efficiency of energy enterprises’ investment merger in the energy Internet sector can be a visual measure of the effectiveness of their investment merger in this sector. It is crucial for energy enterprises to achieve strategic transformation and expand their market share. To this end, this study aims to investigate the efficiency of energy enterprises’ investment merger in the energy Internet sector by constructing an efficiency evaluation index system and evaluation model with the characteristics of the sector. Based on which the TOPSIS model is used to distinguish the differences in the efficiency of the same enterprises’ investment merger in different years. The results of the validation on international power enterprises show that the size of the enterprise has an important influence on its investment merger efficiency in this field. In addition, the evaluation index system and method constructed prove to be effective in evaluating and differentiating the annual investment merger efficiency of energy enterprises in the energy Internet field.