Excitation wavelength dependent visible photoluminescence of CdO nanomorphotypes

We report the red-shifted photoluminescence (PL) band edge emission behavior as a function of subsequent increment in excitation wavelength on cadmium oxide (CdO) nanoflakes and nanoparallelepiped morphotypes prepared through the hydrothermal method. The unusual band edge PL emission lines in crystalline nanomaterials are explained as strong quantum size effect due to the size selective band gap widening in nanomaterials. This kind of excitation wavelength dependent PL emission behavior appears to be in violation of Kasha׳s rule of excitation wavelength independence of the emission spectrum. The surface morphology, particle size, molecular structure, chemical composition and chemical bonding of the samples are analyzed by SEM, TEM, XRD, EDS and FTIR spectroscopy. Direct optical band gap is calculated and found to be of 2.75 eV for nanoflakes and 2.52 eV for parallelepiped nanostructures.