Blue-shift in the optical band gap of sol-gel derived Zn(1-x)SrxO nanoparticles

摘要

Zn(1-x)SrxO nanoparticles (x = 0.00, 00.01, 0.02, 0.03, 0.05) are prepared by sol-gel co-precipitation. Strontium (Sr) doping causes small but highly significant band gap enhancement that amounts 0.58%. This band gap engineering, following a quartic variation with respect to dopant concentration (x), may find potential applications in the fabrication of various devices based on heterojunctions. The structural analysis of the nanoparticles is done using XRD. The randomly oriented polycrystalline nanoparticles (NPs) notice a decrease in lattice parameters for initial two doping levels, thereafter an increment. The crystallite sizes range between 10.54 and 27.76 nm, along various crystallographic planes. Due to Sr doping, dislocations are also caused whose density vary between 1.2 x 10(15) and 9.0 x 10(15) lines/m(2). FTIR analysis confirms the presence of Zn-O bond prominently in tetrahedral mode. UV-Vis spectra reveal a dip at the wavelength corresponding to the band gap of NPs with different Sr concentration. Tauc's plot yields the band gap of undoped ZnO as 3.281 eV which gets augmented up to 3.30 eV by 5 at.% Sr doping. This band gap enhancement is an outcome of infiltration of Sr into the ZnO matrix, rather than substitution. PL emission spectra contain the peaks in UV and visible (violet-blue) range. The UV peak, arising from band-to-band exciton recombination, gets blue-shifted with Sr incorporation into ZnO. Violet-blue emissions, mainly originating from defect levels, see the changes only in their intensities. The surface morphology, through FESEM, presents elongated spherical, hexagonal and platelet kind of structures with interlinking granular chains. Interlinks densify with initial doping, whose role has been comprehended in governing the violet-blue emission. Sr doping of 3 at.% is found to have larger voids in the granular distribution. For highest doping interlinkages appear to resume. For compositional analysis EDX is performed, which confirms the pres