Carbon dots have been widely noticed due to their excellent optical properties, such as good photostability and a wide excitation wavelength range. However, the emission peaks of most known carbon dots (CDs) are in the blue region, which hinders their extensive applications in long-wavelength emission. In this study, red-emitting carbon dots (RCDs) that are pH-responsive are synthesized using citric acid and urea as precursors, and their fluorescence intensity increased gradually with increasing solution pH from 1 to 12. A new mechanism based on H aggregation and Fermi energy level transfer is proposed to explain the pH-responsive emission of RCDs. In contrast to the narrow response range of most pH-sensitive CDs reported so far, the pH-responsive range of RCDs is large, especially in the alkaline range, and their pronounced red light emission is well visualized. The prepared carbon dots have the advantages of non-toxicity, low cost, and a wide pH response range. In addition, “rose” test paper and carbon dot PVA composite film, RCDs-PVA film, are made to demonstrate the visualization of carbon dots in pH detection. The “rose” test paper and carbon dot PVA still have good fluorescence intensity. The prepared carbon dots have good application prospects for pH detection.

中文翻译：

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一步制备氮掺杂碳点荧光传感器，用于有效检测 pH 值

碳点由于其优异的光学性质（例如良好的光稳定性和宽的激发波长范围）而受到广泛关注。然而，大多数已知碳点（CD）的发射峰位于蓝色区域，这阻碍了它们在长波长发射方面的广泛应用。在本研究中，使用柠檬酸和尿素作为前驱体合成了 pH 响应型红光碳点（RCD），其荧光强度随着溶液 pH 值从 1 增加到 12 而逐渐增强。费米能级转移被提出来解释 RCD 的 pH 响应发射。与迄今为止报道的大多数 pH 敏感 CD 的窄响应范围相比，RCD 的 pH 响应范围很大，尤其是在碱性范围内，并且其明显的红光发射清晰可见。所制备的碳点具有无毒、成本低、pH响应范围宽等优点。此外，还制作了“玫瑰”试纸和碳点PVA复合膜、RCDs-PVA膜，演示了碳点在pH检测中的可视化。“玫瑰”试纸和碳点PVA仍然具有良好的荧光强度。制备的碳点在pH检测方面具有良好的应用前景。