Defects induced multicolor down- and up-conversion fluorescence in Se doped ZnO nanorods by single wavelength excitation

Se doped ZnO nanorods prepared by mechanothermal method with generation of multiple zinc (V-Zn), oxygen (V-O) vacancies and oxygen interstitials (O-i) defects induce multicolor emissions by single and two-photon single wavelength excitations. The photoluminescence spectrum under single-photon excitation exhibits a broad multicolor emission peak from 400 to 800 nm with lambda(max) at similar to 625 nm and a large Stokes shift of about 250 nm due to overlapping of defects in electronic transitions. The de-convolution peaks within superposition of defects (V-Zn, V-O and O-i) induce multicolor broadband emission to show blue, green and red emissions that are consistent with their corresponding defects. The EPR signals also reveal detail information about these defects and show correlation with optical electronic transition states of blue, green and red emissions in Se doped ZnO NRs. Moreover, the two-photon up-conversion luminescence of Se doped ZnO NRs also shows multicolor (blue, green and red) emissions from channel at 720 nm excitation. Two-photon confocal studies of Se doped ZnO NRs shows multicolor emission at 720, 800 and 860 nm excitations which are consistent with one photon fluorescence at 360, 400 and 430 nm excitations. Therefore, these defects induced multicolor emissions by one and two-photon excitation wavelengths have potential optoelectronic and biomedical applications.