[en] Absolute energies of band edges have proven to be very important for various applications like hydrogen generation, solar water splitting and solar cell optimization. Energy differences as small as 50–100 meV have been shown to largely affect device efficiencies. Device operational temperature can vary largely and temperature dependence of band gap is well known in bulk semiconductor literature. However, there are only a few studies on variation of band gap in quantum dots and none of them characterize the relative energy variation of band edges in spite of their importance in various applications. This is mainly due to the absence of an internal standard that can be used to study the variation of band edges. Here, in this paper, we introduce a technique wherein we utilize Cu dopant emission as an internal probe. Using this technique, we report the variation of band gap, conduction band and valence band edges of CdS and CdSe quantum dots as a function of temperature and size. We found that band gap variation is similar to that of bulk but with a higher average phonon energy. The band edge variation is characterized by a dominant conduction band shift for larger sizes with decreasing temperature while the smaller size QDs show the variation in both conduction band and valence band. Further, we have also utilized this method to study the binding energy of the trap states as a function of temperature using Cu photoluminescence quantum yield and average lifetime of Cu photoluminescence. (paper)