The nature of carbon quantum dot (CD) luminescence is still broadly investigated based on different CD synthesis processes. This study aims at investigating the effect of microwave power on optical characteristics of CDs using microwave radiation techniques. CDs are synthesized with citric acid as a source of carbon and urea as a passivation agent. CDs have been successfully synthesized, and an increase in the CD burn-off percentage was observed with an increase in the microwave power. The TEM test results show that the dimensions of the CDs resulted are in the range of 3.4–9.5 nm with an average size of 6 nm at 450 W. The results of the FTIR functional group structural analysis show that a CD has N—H and O—H stretching bonds. According to the results of UV–Vis analysis, the CDs have absorption peaks at 335 nm and 407 nm, which indicates a π → π^* electronic transition from the C=C bond and an n → π^* transition from the C=O bond. Using the Tauc-plot method, the CD energy bandgap values were found to be 2.47 eV, 2.51 eV, 2.51 eV, 2.52 eV, and 2.53 eV at CD 300, CD 450, CD 600, CD 850, and CD 1000, respectively. The optical multichannel analyzer test results show that the peak emission waves produced by CDs are 536 nm and 532 nm with the strongest bright green light at CD 1000. Time-resolved photoluminescence testing shows that the CD decay time generally ranges from 5 ns. Overall, an increase in the microwave power causes an increase in the percentage of burn-off, energy bandgap, absorption intensity, and CD emission intensity.

中文翻译：

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高绿色发射碳点及其光学特性：微波功率效应

碳量子点（CD）发光的性质仍然基于不同的CD合成过程进行了广泛的研究。这项研究旨在研究使用微波辐射技术的微波功率对CD光学特性的影响。CD以柠檬酸为碳源，尿素为钝化剂合成。CD已成功合成，并且随着微波功率的增加，CD燃尽百分比增加。TEM测试结果表明，所得CD的尺寸在3.4–9.5 nm范围内，在450 W时平均尺寸为6nm。FTIR官能团结构分析的结果表明CD具有NH和OH拉伸键。根据UV-Vis分析的结果，CD具有在335 nm和407 nm处的吸收峰，表明π→π^*来自C = C键的电子跃迁和n→π ^*来自C = O键的跃迁。使用Tauc-plot方法，发现CD 300，CD 450，CD 600，CD 850和CD 1000的CD能带隙值分别为2.47 eV，2.51 eV，2.51 eV，2.52 eV和2.53 eV。光学多通道分析仪的测试结果表明，CD产生的峰值发射波为536 nm和532 nm，CD 1000处的亮绿色光最强。时间分辨光致发光测试表明CD的衰减时间通常为5 ns。总体而言，微波功率的增加导致燃尽百分比，能带隙，吸收强度和CD发射强度的增加。