Question

How would the conduction band and valence band energies change if the Se in these quantum dots were replaced with O (CdO vs. CdSe)?

Answer 1

Before answering the question, let us ask ourselves what do we mean by the term "band gap". It simply refers to the difference in energy levels between the lower part of conduction band and the upper part of valence band. Having said that, the band gap of CdSe is 1.74 eV while the band gap of CdO is 2.2 eV with conduction band energy being -4.61 eV. If Se in these quantum dots were to be replaced with O, the band gap increases which means fewer electrons possess the energy to cross over to the conduction band and produce current. This results in some loss of properties of the semiconductor as its typical value for band gap is around 1 eV and by replacing with O only broadens the band gap further.