Selective Processing And Luminescent Behavior Of Rare Arth Basic Nitrates

In this dissertation,the synthesis of the monoclinic RE4O(OH)9NO3 and tetragonal RE(OH)2.94(NO3)0.06·nH2O(Ln=rare earth,Y)were achieved via controlled hydrothermal processing,with emphases on processing window,particle morphology control,formation mechanism and physicochemical properties.The effects of particle morphology(size and shape),crystal structure,tunable color,anion exchange and Eu3+ coordination on photoluminescence of the resultant micro-/nano-phosphors have been systematically investigated.Detailed characterizations of the products were performed by the combined techniques of XRD,FT-IR,FE-SEM,TEM,SAED and PLE/PL analysis,and the main achievements are listed as follows.Monoclinic RE4O(OH)9NO3(RE=Y,Tb,Dy,Ho,Er,Tm,Yb and Lu)were hydrothermally synthesized at 180℃ for 24h with pH 7-8,and the morphologies of the products are microwires hexagonal prisms.Under the same condition,hexagonal RE(OH)3(RE=La,Pr,Nd,Sm,Eu and Gd)microrods are the resulting products.On the other hand,tetragonal Ln(OH)2.94(NO3)0.06·nH2O(RE=Y;Ho,Er,Tm,Yb and Lu)were hydrothermally synthesized at 180℃ for 24h and pH 10～11,the resulting products are square nanoplates.Under the same condition,hexagonal RE(OH)3(RE=La,Pr,Nd,Sm,Eu,Gd,Tb and Dy)microrods are the resulting products.While RE=Ce,the resulting product is CeO2.Systematic study found that RE(OH)3 can be converted into RE2(OH)5NO3·nH2O(LRH)in the presence of NH4NO3,but RE4O(OH)9NO3 and RE(OH)2.94(NO3)0.06·nH2O can not be obtained.(Ln0.95Eu0.05)(OH)3(Ln=La,Gd)and(Ln0.95Eu0.05)4O(OH)9NO3(Ln=Y,Lu)exhibit luminescent properties closely related to their crystal structure and the site symmetry of Eu3+.(Ln0.95Eu0.05)(OH)3(Ln=La,Gd)is hexagonal in structure and consists of 9-coordinated Eu3+ions in D3h symmetry.The centrosymmetric high site symmetry thus causes weaker intensity of 5D0-7F2 transition than that of 5D0-7F1 one in the absence of the 5D0-7F0 one.The(Ln0.95Eu0.05)4O(OH)9NO3(Ln=Y,Lu)is monoclinic structured and consists of 7-coordinated Eu3+ ions in C2v non-centrosymmetric sites and 9-coordinated Eu3+ ions in D3h centrosymmetric sites.The higher occupancy of C2v symmetry(C2v/D3h=3)thus makes the intensity of 5D0-7F2 transition stronger than that of 5D0-7F1 one.The(Y0.95Eu0.05)4O(OH)9NO3 was used as template to anion exchange with VO3-,BO3-and F-through hydrothermal processing,which found that significantly improved luminescent intensity can be obtained by ion exchange with VO3-while maintaining the original morphology and crystal structure.Dense oxide luminescent films have been successfully fabricated by spin coating the suspension containing(Y0.99-xTb0.01Eux)(OH)2.94(NO3)0.06·nH2O square nanoplates on quartz substrate followed by calcining at 600℃ for 2h.The results showed that Tb3+can effectively transfer energy to Eu3+,and the maximum efficiency of Tb3+→Eu3+energy transfer was found to be 35.8%for the(Y0.95Tb0.01Eu0.04)2O3 composition.The emission color of the oxide phosphors can be widely tuned from green via yellow to red with increasing Eu incorporation.At the same time,tetragonal nanosheets were used as templates to exchange ions with pa,which found that pa could partially or completely replace NO3-without changing the particle morphologies and the crystal structure,with R=0.25(R is the molar ratio of pa to rare earth ions).However,greatly enhanced luminescent intensity was found for the resultant products.