Hydrothermal Synthesis And Photoluminescence Property Study Of The Samarium Orthovanadate Nanocrystals

In this thesis,the dodecahedron-shape,octahedron-shape and particle-shape SmVO4 nanocrystals were prepared through a simple hydrothermal method by adding suitable KOH and urea,respectively.In order to obtain the dodecahedron-shape SmVO4 nanocrystals,a series of experiments were carried out to determine the optimum reaction conditions of hydrothermal synthesis.The structure and morphology of the dodecahedron-shape SmVO4 nanocrystals were characterized and analyzed through powder X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),Fourier transform infrared(FTIR)spectroscopy,field emission scanning electron microscopy(FESEM)and high-resolution transmission electron microscopy(HRTEM).The possible growth mechanism of the dodecahedron-shape SmVO4 nanocrystals was also proposed.Besides,the effects of the additives,KOH and urea,in the process of the crystal growth was explained.The photoluminescence properties of the dodecahedron-shape,octahedron-shape and particle-shape SmVO4 nanocrystals were compared and studied.Furthermore,the dodecahedron-shape SmVO4 nanocrystals as the hosts doped with different rare earth ions in the same amounts and same rare earth ions in different amounts respectively.And their photoluminescence properties were also compared.The results would provide guidance on the basis for the practical application of SmVO4 nanocrystals as luminescent materials.The main research results of the thesis were summarized as two parts.1.The dodecahedron-shape,octahedron-shape and particle-shape SmVO4 nanocrystals have been successfully prepared through a facile hydrothermal method by adding suitable KOH and urea,respectively.The synthesis method is simple and feasible and it may be used for preparing other rare earth orthovanadate with the similar shape.Then the condition experiments were carried out by prepare dodecahedron-shape SmVO4 nanocrystals with uniform size and morphology.The results showed that 240 ?,2 days and the molar ratio of Sm(NO3)3·6H2O to NH4VO3 of 1:1 were the preferable experiment parameters for preparing dodecahedral SmVO4 nanocrystals.Meanwhile,the influence of two additives,KOH and urea,in the process of crystal growth for products with different shape was researched.And the result revealed that the product was dodecahedron-shape when KOH was added with 2.5g and urea was 1.0g,the product was octahedron-shape when KOH was 0.2g and urea was 0.5g with the reaction temperature enhanced to 260 ?,and the product was particle-shape when KOH and urea were not added.The obtained products with dodecahedron-shape were characterized by XRD,XPS,FTIR,FESEM and HRTEM.The results indicated that all the SmVO4 nanocrystals were pure-phase and well-crystallinity.The morphologies of the SmVO4 nanocrystals were close to dodecahedron with the length around hundreds of nanometers.In addition,the possible growth mechanism of dodecahedral SmVO4 nanocrystals was proposed.The important influence of two additives,KOH and urea,was revealed for the growth of dodecahedron-shaped SmVO4 nanocrystals.2.The photoluminescence(PL)properties of SmVO4 nanocrystals with different shapes including dodecahedron-shape,octahedron-shape and particle-shape were studied by steady-state/lifetime spectrofluorometer at room temperature.The results indicated that SmVO4 nanocrystals with different shapes would all emitted green light at 564 nm,orange light at 601 nm and red light at 645 nm under 315 nm excitation.And it was attributed to the intra-configurational 4f electron transitions of Sm3+ ions.However,SmVO4 nanocrystals with different shapes had different emission intensity and dodecahedral SmVO4 nanocrystals performed best emission intensity compared with the other two shapes,because the energy transfer from VO43-to Sm3+ is quite more complete and efficient in dodecahedral SmVO4 nanocrystals.Besides,dodecahedral SmVO4 nanocrystals as the hosts doped with different rare earth ions by same concentration(5%Er3+?5%Dy3+?5%Eu3+)and doped with different concentration by Eu3+ ions(1%?3%?5%?7%)were synthesized and their PL properties were compared.The results indicated that dodecahedral SmVO4 nanocrystals doped with 5%Eu3+ performed more complex PL properties from Eu3+ and Sm3+ ions,but dodecahedral SmVO4 nanocrystals doped with 5%Er3+ or 5%Dy3+ only performed simple PL properties from Sm3+ ions.And the results demonstrated that dodecahedral SmVO4 nanocrystals doped with 7%Eu3+ performed strongest emission intensity compared with all other dodecahedral SmVO4 nanocrystals doped with Eu3+ in different concentration(1%,3%,5%),which means SmVO4:7%Eu3+ nanocrystals would possess more extensive pratical application in optical devices.