Study The Modulation Of Energy Gap For Rare Earth Doped ZnO By Theory And Experiment

As a kind of wide band-gap semiconductor, nano-structured ZnOshow novel properties, which make ZnO a kind of promising materialwidely used in photoelectric devise, catalysis, rubber, ceramic andmake-up industry, and received more and more intensive interests. It isthe key problem for the doping in ZnO for fully using its shape,energylevels and novel properties in recent years, it will be significative to studythe modulation of energy gap and improve properties by doping rare earth,which is a special dopant.In this paper, ZnO and La³⁺ doped ZnO crystals with different La³⁺doped concentrations (0.5％, 1.0％, 1.5％, 2.0％, 2.5％, 3.0％, 4.0％,5.0％) were prepared by solventthermal method. The influence ofimpurities on the crystal structure and optical property were investigated.There were no new peaks in the doped-crystal X ray diffraction patterns,but the intensity and the position of peak are different from pure one, sothe doped ions altered the lattice parameters and maked the lattice volume increase. At the same time, XRD results also show that the diffractionpeak widened and intensity decreased with the increase of rare earthconcentrations in the ZnO. nanocrystals which means that the size of theZnO nanocrystals decreased. So the doping of rare earth ions can holdback the growth of ZnO nanocrystals. Ultraviolet-Visiable diffusereflenctance spectrum revealed: La³⁺ doped make the absorption edgeshift to the shorter wavelength, and broaden the energy gap, and energygap get more and more big with the increase of rare earth concentrationsin the ZnO until up to 2.0％. The characteristic photoluminescence ofZnO was observed in La³⁺ doped ZnO nanocrystals. Strong yellow andred photoluminescence was observed in 2.0％La³⁺ doped ZnOnanocrystals by irradiated with light belong to 403 and 447nm, So we cansee the doping La³⁺ ions can affect the visible photoluminescence of ZnOnanocrystals. We also test the photocatalyst activity of ZnO and La³⁺doped ZnO, our sample have strong photocatalyst activity forphotodegrated methylene blue, and the photodegradation is mostcompletely by ZnO with 2.0％La³⁺ doped.At the same time, the plane-wave pseudopotential method of DensityFunctional Theory is used to study the energy band structure, thedensities of states and electronic properties of pure ZnO and La dopedZnO crystals, Compared with the analysis result, research theirconnectivity. Calculation results showed that those impurities influnced the energy band structure, the densities of states and electronic propertiesof pure ZnO crystal. And we can know from the calculation result that theenergy gap was broadened after La³⁺ doped in ZnO crystal, the result issame to the experiment data.