Studies On Fabrication And Photoluminescence Of Rare-earth Fluoride Nanostructures And Their Core-shell Structures

Rare-earth fluoride nanocrystals have received extensive attention due to their unusual properties and potential applications in optics,optoelectronics,biological labeling,catalysis fields,etc.However,it still remains a great challenge to precisely control the size,morphology,and crystal structure of rare-earth fluorides for tailoring their relative properties,especially photoluminescence.Besides,crystal structure is one of the most important factors that can influence the photoluminescence of rare-earth fluoride nanocrystals,so we are concerned about the direct correlation between the crystal structure of the rare-earth fluorides and their morphologies.Otherwise,core-shell nanoparticles are novel ordered assembly structures on nanometer scale,which are synthesized through chemical bond or other interaction between two materials.The surface charge,functional groups,and properties of core materials are tailored by coating of shell materials,which improves stabilization and dispersion of core materials.The photoluminescence of core-shell nanoparticles would be enhanced by doping or surface plasmon resonance,which exhibits potential applications in biological labels and other fields.In the thesis,EuF₃ and LaF₃:Eu nanostructures have been fabricated successfully, as well as Au@SiO₂,Au@SiO₂@LaF₃:Eu,and Au@SiO₂@CdTe core-shell nanoparticles by low temperature chemical reaction.The morphology,crystalline structure and optical properties of these nanostructures and core-shell nanoparticles were investigated with TEM,FESEM,XRD,UV-Vis and PL.The main results achieved in this paper are listed as following:1.EuF₃ nanostructures were synthesized by low temperature chemical reaction. Polyelectrolytes had greatly influenced on the morphologies of the EuF₃ nanostructures.The hexagonal doughnut-like EuF₃ nanostructures with the diameter of about 200～300 nm had been spontaneously transformed into orthorhombic spindle-like EuF₃ nanostructures with the diameters of about 100 nm and length of 250～400 nm with the extension of the reaction time usging PSS as polyelectrolyte. The PL analysis indicated that the two different EuF₃ nanostructures exhibited the similar PL properties.Morever,disk-like LaF₃:Eu nanostructures were also synthesized by low temperature chemical reaction.Polyelectrolytes shows little effect on the morphologies,the crystalline structures and PL pesks of LaF₃:Eu.However,PL intensities were controlled by the polyelectrolytes due to their different capping ability.2.Au colloids with 10 -70 nm size were synthesized by low temperature chemical reaction using sodium citrate as a reductant.The size increase of Au resulted in the red-shift of surface plasmon resonance peak of Au from 520 nm to 540 nm. Then Au@SiO₂ core-shell nanoparticles were obtained through coating SiO₂ on colloidal Au surface by a Stober method.The SiO₂ coating also made surface plasmon resonance peak of Au red-shift.3.Au@SiO₂@LaF₃:Eu core-shell nanoparticles were synthesized by in-situ chemical reaction.With the increase of SiO₂ layer thickness,the PL intensity of Au@SiO₂@LaF₃:Eu core-shell nanoparticles increased at first,and then decreased when the thickness of SiO₂ layer was equal to the size of Au core,as well as the lifetime.Morever,their PL intensity and lifetime were both different from those of LaF₃:Eu nanoparticles.4.Au@SiO₂@CdTe core-shell nanoparticles were synthesized by LBL method. With the increase of SiO₂ layer thickness,their PL intensity increased at first,and then decreased when the thickness of SiO₂ layer was equal to the size of Au core.However, their lifetime decreased all the time with the increase of SiO₂ layer thickness.Morever, their PL intensity and lifetime were both different from those of CdTe quantum-dots, especially the lifetime.