| Nanoparticles exhibit small size effect,surface effect,quantum size effect and quantum tunneling effect owing to the small volume,large specific surface area,high surface atomic occupancy,high surface energy,special electronic structure of unsaturated and suspended bonds,which make them possess unique physical and chemical properties that significantly different from those of corresponding traditional materials.Therefore,it has many unusual physical and chemical characteristics different from traditional materials.ZnAl2O4 is a typical mixed transition-metal oxide with the spinel structure,belonging to a direct wide band gap semiconductor material with a band gap of～3.8 eV.This type of materials has many advantageous properties such as high mechanical and thermal resistance,high chemical and thermal stability,low temperature sinter ability,low surface acidity,hydrophobic behavior,good diffusion,and high quantum yields.ZnAl2O4 has wide application prospect in transparent ceramics,catalyst and catalyst supports,optical materials,dielectrics and sensing,and so on.In addition,the transition metal ions dopping method can be used to adjust the crystal structure and energy band structure of the semiconductor,control crystal quality,charge carrier and concentration of defects in ZnAlO4 and regulate the type and concentration of carriers or local carrier conditions,prepare uniformly doped ZnAl2O4 nanocrystalline,thus the micro structure,optical,electrical and magnetic properties of the doped ZnAl2O4 can be effectively inproved.In this thesis,the doped ZnAl2O4 with a series of transition metal ions such as Ni,Co,Fe,Cu and Mn into the Zn ions and A1 ions were prepared by wet chemical method.The crystal structure,morphology,specific surface area,chemical composition,ions valence state,optical property and magnetism property of the samples were characterized by XRD,SEM,BET,SAED,HRTEM,EDX,STEM-EDX Mapping,FT-IR,XPS,UV-vis,PL and VSM.At the same time,the band structure and density of states were calculated specifically by means of the first-principles calculations.And then we give the microscopic mechanisms of PL and UV-vis spectra of the transition netal doped ZnAl2O4.The research contents are as follows:(1)ZnAl2O4 nano materials were synthesized by hydrothermal method and sol-gel method.And the crystal structure,band structure,electronic structure and optical properties of the ZnAl2O4 nano materials,which prepared under different temperature conditions and different preparation methods,were characterized by XRD,HRTEM,EDX,FT-IR,XPS,PL and UV-vis,respectively.The band structure and density of state of the various defects in ZnAl2O4 were gotten through the first principles calculation.The results show that the band gap value of ZnAl2O4 nanomaterials prepared by sol-gel method is the maximum.and is close to the value of the bulk zinc aluminate.The band gap values of the ZnAl2O4 nano materia ls prepared using the hydrothermal method under the different processing temperature are less than the value of the bulk zinc aluminate.With the aid of the energy band structures obtained by first-principles calculations,the relationship between the luminescence spectra,defect state structures and the detailed transition of specific energy levels are discussed.(2)Zn1-xNixAl2O4(x=0,0.025,0.05,0.075 and 0.10)nanopowders were synthesized by sol-gel method.The results of XRD and FT-IR show the samples have no impurity phase and keep the pinel structure;SEM show the samples are dandruff-like morphology;The fitted XPS spectra demonstrate that the doped Ni ions occupy the A sites and B sites of the spinel structure.The UV-vis spectra show that the band gap values of samples decrease with the increase of Ni concentration;The PL spectra give that the photo luminescence quenching is occurred with the increasing Ni doping concentration and this phenomenon can be explained well by the calculated band structures obtained by the first-principles calculations.(3)Zn1-xCoxAl2O4(x=0,0.10,0.20 and 0.40)nanopowders were synthesized by hydrothermal method.The fitted XPS spectra reveal that,at lower Co ions concentration,Co ions preferentially occupy at the B sites,that is the octahedral position;With the increasing of Co ions concentration,the proportion of Co ions occupied A sites increases;With increasing the Co ions,the UV-vis absorption spectra results show the characteristic peaks of Co ions at tetrahedral position appears and the peaks intensity is gradually enhanced;The intensity of luminescence spectra decreases and quenching is occurred with the Co ions doping and this phenomenon can correspond well to the calculated band structures obtained by the first-principles calculations.(4)Zn1-xFe,Al2O4(x=0.0.10.0.20 and 0.30)nanopowders were synthesized by hydrothermal method,and ZnAl2-xFexO4(x=0,0.025,0.05 and 0.10)nanopowders were synthesized by hydrothermal method combined with heat treatment method.The changing law of the spinel characteristic peak,the binding energy of each element,the optical mechanism and the magnetic mechanism under the influence of the Fe dopping on Zn ions and Al ions is researched by combining experiments and theoretical calculations.(5)Zn1-xCuxAl2O4(x=0,0.05,0.10,0.15 and 0.20)nanopowders were synthesized by hydrothermal method combined a heat treatment.The crystal grain size,the lattice constant and the interplanar spacing become smaller with the increase of Cu ions doping concentration;The fitted XPS spectra demonstrate that the doped Cu ions all occupy the A sites of the spinel structure.The luminescence mechanism of samples is explained by combining UV-vis spectra and luminescence spectra with first-principles calculations.(6)Zni1-xMnxAl2O4(x=0,0.10,0.20,0.30,0.40 and 0.50)nanopowders were synthesized by hydrothermal method and Zn(Al2-xMnx)O4(x=0,0.025,0.05 and 0.10)nanopowders were synthesized by hydrothermal method combined with heat treatment method.The XPS results show that Mn dopping on the Zn ions or Al ions could all affect the change of binding energy of each element,and Mn occupy in tetrahedral and octahedral position;The UV-vis spectra show that,with the increase of Mn content,the absorption spectra intensity of the samples is gradually enhanced,new absorption peaks appeare and the band gap values of the materials gradually decrease;PL spectra show that Mn dopping also causes luminescence quenching,which corresponds well to the result of first-principles calculations;Room temperature VSM results show the samples of Mn doped Zn ions exhibit antiferromagnetic behavior while the samples of Mn doped Al ions exhibit paramagnetic behavior. |
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