Photophysical properties of doped carbon dots (N, P, and B) and their influence on electron/hole transfer in carbon dots–nickel (II) phthalocyanine conjugates

Abstract

Doping in carbon nanomaterial with various hetero atoms draws attention due to their tunable properties. Herein, we have synthesized nitrogen containing carbon dots [C-dots (N)], phosphorus co-doped nitrogen containing carbon dots [C-dots (N, P)], and boron co-doped nitrogen containing carbon dots [C-dots (N, B)]; and detailed elemental analysis has been unveiled by X-ray photoelectron spectroscopy (XPS) measurements. Our emphasis is given to understand the effect of doping on the photophysical behavior of carbon dots by using steady-state and time-resolved spectroscopy. Nitrogen containing carbon dots have quantum yield (QY) of 64.0% with an average decay time of 12.8 ns. Photophysical properties (radiative decay rate and average decay time) are found to be increased for phosphorus co-doping carbon dots due to extra electron incorporation for n-type doping (phosphorus dopant) to carbon dots which favors the radiative relaxation pathways. On the contrary, boron (p-type dopant) co-doping with nitrogen containing carbon dots favors the nonradiative electron–hole recombination pathways due to incorporation of excess hole; as a result QY, radiative rate, and average decay time are decreased. To understand the effect of doping on charge transfer phenomena, we have attached nickel (II) phthalocyanine on the surface of C-dots. It is seen that phosphorus co-doping carbon dots accelerates the electron transfer process from carbon dots to phthalocyanine. In contrast, after boron co-doping in carbon dots, the electron transfer process slows down and a simultaneous hole transfer process occurs.