Luminescent carbon nanodots (CDs) are attracting great interests due to their unique properties in physics and chemistry. In this study we present the experimental evidences of the significant roles of self–absorption and radiative energy transfer in the photoluminescence process of N–doped CDs in water. It is found that the PL spectra, especially the relative intensity between the UV and visible bands, which are the major spectral structures, show a distinctive dependence on the concentrations of CDs, and can be well understood with the well–known Beer–Lambert law. These findings could be very helpful to deepen the existing understanding of the complex luminescence mechanisms of CDs.
