Cadmium selenide, CdSe, is used as a photoconductor in lightmeters. The band gap is about 1.74 eV. Explain what is the longest wavelength of light that can promote an electron from the valence band to the conduction band in cadmium selenide? Nanoparticles of CdSe exhibit luminescence with a color dependent upon their size. Explain why does the wavelength of light emitted by CdSe nano particles shift from red to green as particle size is reduced? Explain what is this phenomena called?