Two-photon emission of fluorescent carbon quantum dots made of urea and trisodium citrate

Abstract

Carbon quantum dots, which produce good fluorescence, are potential for many applications, including biomedical applications. In biomedical researches, many quantum dots have been utilized and explored under the two-photon emission mechanism. This mechanism allows living tissue to survive from the excitation laser used in the procedure. The study on the two-photon emission mechanism of carbon quantum dots is rarely done by other researchers. Therefore, in this work, we focused on synthesizing carbon quantum dots from urea and trisodium citrate and studying their optical properties under one-photon and two-photon emission mechanisms. We found that using higher photon energy, we were able to excite carbon quantum dots to get emissions at lower photon energy. Cyan until green emission colours were observed under the one-photon mechanism. Furthermore, we also found that carbon quantum dots can emit fluorescence at higher photon energy when they were excited using lower photon energy. This was the evidence that carbon quantum dots were also able to be excited using the two-photon mechanism. From absorbance and photoluminescence spectra, we were able to predict the energy band level of the carbon quantum dots. This work could give further clues for the application of carbon quantum dots in biomedical applications.