Nitrogen-doped carbon dots (CDts) with tunable fluorescence properties in aqueous media were synthesized hydrothermally. The excitation wavelength variation to obtain the maximum emission produced a blue shift in the emission peaks upon dilution in an aqueous solution. The shift can be explained by a re-absorption phenomenon in a concentrated solution. The interparticle interaction within was responsible to show dilution-dependent optical behavior. The as-synthesized solution of CDts did not show any prominent absorption peak over a wide range. However, upon dilution, two peaks became predominant. The concentration-dependent behavior was observed during the interaction with metal cations. Cationic salts of Co(II) and Hg(II) caused quenching at different dilutions of CDts. This might be explained by the exposure of different surface functional groups during dilution and metal-ion–CDts charge transfer. The quenched fluorescence of CDts was rescued using ascorbic acid. Therefore, the one-pot detection of Co(II)/Hg(II) and ascorbic acid was designed through a ‘Turn Off/On’ phenomenon.

水热合成具有可调荧光特性的氮掺杂碳点（CDts）。在水溶液中稀释后，获得最大发射的激发波长变化在发射峰中产生蓝移。可以用浓溶液中的重吸收现象来解释这种变化。内部的粒子间相互作用负责显示依赖稀释的光学行为。CDts的合成溶液在宽范围内均未显示任何突出的吸收峰。然而，稀释后，两个峰成为主要峰。与金属阳离子相互作用期间观察到浓度依赖性行为。Co（II）和Hg（II）的阳离子盐在CDts的不同稀释度下引起淬灭。可以通过稀释和金属离子CDts电荷转移过程中不同表面官能团的暴露来解释。使用抗坏血酸拯救CDts的猝灭荧光。因此，通过“关闭/打开”现象设计了一锅法检测Co（II）/ Hg（II）和抗坏血酸。