Anion Exchange Of Layered Rare Earth Hydroxides And Study On The Properties Of Its Exchange Products

Layered rare earth hydroxides（LRH）has been widely concerned because of the advantages and characteristics of both rare-earth materials and layered compounds.LRH is an ideal candidate for the preparation of fluorescent films because of its typical two-dimensional morphology.However,at present,the most commonly used"four-step film forming"method to prepare LRH films has many steps,long cycle and low yield.In addition,LRH structure contains groups that quench fluorescence（crystal water,hydroxyl group and nitrate ion）,so it is very necessary to fluorescent modification.In this thesis,LRH film was synthesized in one step by electrodeposition for the above problems,molybdate ion(Mo O₄^2-)was selected as the anion source for anion exchange to achieve fluorescence optimization.The main research work is as follows:（1）A series of RE₂（OH）₅NO₃·n H₂O（RE=La,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho and Y）films were synthesized by electrodeposition at room temperature,and the effect of“lanthanide shrinkage”on the structure and morphology of LRH was determined.Taking the exchange reaction of LEu H thin film with Mo O₄^2-as an example,it is clear that the concentration of Mo O₄^2-is the key factor affecting the phase and morphology of the exchange products.The interlayer anion exchange product Eu₂（OH）₅（Mo O₄）_0.5·n H₂O and lamellar anion exchange product Na Eu（Mo O₄）₂ were obtained by adjusting the concentration,reaction time and reaction temperature of Mo O₄^2-.By studying the fluorescence properties of LEu H film and its exchange products,it was found that the fluorescence properties of the exchange products were better than that of LEu H,and the red emission intensity of the interlayer anion exchange products was 2 times of that of LEu H.The red emission intensity of the lamellar anion exchange film was 78 times that of LEu H.（2）LLa H film prepared by electrodeposition was used as precursor,and Na La（Mo O₄）₂ film was prepared at p H～7 at 150℃with Na₂Mo O₄（2 M,40 ml）as anion source.By changing the reaction time,the evolution process of phase and morphology from LLa H to Na La（Mo O₄）₂ was revealed,and the mechanism of"dissolution and recrystallization"in the process of phase transformation was clarified.In addition,the influence of lanthanide shrinkage on the structural characteristics and morphology of Na RE（Mo O₄）₂（RE=La,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho and Y）films was clarified.By regulating the concentration and proportion of Eu³⁺and Tb³⁺dopant ions in Na La（Mo O₄）₂ matrix,fluorescence color tuning from green-yellow-red can be achieved,and the mechanism of energy transfer effect from Tb³⁺to Eu³⁺is described.（3）Since Gd³⁺ions can also transfer energy to rare earth luminescent ions,Na Gd（Mo O₄）₂ was selected as the luminescent substrate in this chapter.By doping Eu³⁺and Tm³⁺,Dy³⁺,Eu³⁺co-doping in Na Gd（Mo O₄）₂ matrix and regulating the ratio of luminescent ions,white light emitting fluorescent films can be obtained.The CIE coordinates of Na(Gd_0.94Tm_0.01Dy_0.05)（Mo O₄）₂ thin films was（0.315,0.329）are close to the standard white light when excited at 351 nm.