Spectroscopy Studies, The Effect Of Energy Transfer Between Ions. Nanocrystals Doped

Luminescent materials based on lanthanide ions have been widely used as phosphors in lamps and display, components in optical communication, and active materials in laser devices. Crystalline and amorphous materials are matrixes frequently used for lanthanide ions. As a new material developped these years, the excellent combination of chemical advantages of crystal host with optical advantages of lanthanide ions enhances the application of lanthanide doped optical materials significantly. Lanthanide doped material is one of the most important luminescence materials.Many studies showed that there existed energy transfer between doped ions or doped ions and the matrix in codoped systems,which resulted in exotic states and sensitizing actions. Different matrixs or synthetic methods can directly influence the radiative properties of the materials.So far, studies about energy transfer between lanthanide ions, especially in luminescence nanocrystal materials are limited.But these materials might have great potentials in the future applications. Trivalent Tm³⁺ and Pr³⁺ have attrctive radiations in visible and infrared wave band. There are many reports about fluorescence and its mechanism ont Tm³⁺ and Pr³⁺ doped in nanocrystals,crystals,glasses and optical fibers. The transitions from ¹D₂ to ³F₄ of Tm³⁺ and from ³P₀ to ³H₄ of Pr³⁺ lies in green region, which show great significance in data storage,information technology,laser pritingN colour display,and medical treatments. So investigations on Tm³⁺ and Pr³⁺ ions doped or codoped materials attracted lots of researchers. Expected fluorescence emission with designed property and application could be obtained by properly selecting doped ions and matrix.In this thesis, energy transfer between Pr³⁺ and Tm³⁺have been investigated in fluoride and oxyfluoride nanocrystals. The thesis includes four parts.Part One:Hydro-thermal and Solvent-thermal Methods are simple ways to synthesize nanocrystals. In this part, the methods employed to synthesize the doped nanoparticles at low temperatures are presented. Factors influcing the growth of nanocrystals have also been invesgated too. Nanocrystals with good dispersion and uniform distribution are prepared with these methods, and characterized with XRD,AFM and TEM. Part Two:The optical emissions of LaF₃:Pr³⁺/Tm³⁺ nanocrystals were studied with laser spectroscopic method. The excitation light is 355 nm pulsed laser.Fluorescence emissions resulted from the energy transfer between Pr³⁺ and Tm³⁺ in LaF₃ nanocrystals were observed, the corresponding mechanism is discussed.The influence of ion concetration and environmental temperature on the energy transfer are investigated.It was found that increasing the concentration of Pr³⁺, or reducing environment temperature of samples, can enhance the energy transfer between Pr³⁺ and Tm³⁺ when Tm³⁺ was excited.Part Three:The optical emissions of LaOF: Pr³⁺/Tm³⁺nanocrystals were studied with laser spectroscopic method. The excitation light is 355 nm pulsed laser.Fluorescence emissions resulted from the energy transfer between Pr³⁺ and Tm³⁺ in LaOF nanocrystals were observed, the corresponding mechanism is discussed.The influence of ion concetration and environmental temperature on the energy transfer are investigated.It was found that increasing the concentration of Pr³⁺, or reducing environment temperature of samples, can enhance the energy transfer between Pr³⁺ and Tm³⁺ when Tm³⁺ was excited.Part Four:Considering that LaF₃/LaOF nanocrystals codoped with Pr³⁺and Tm³⁺ as objects of studying,we discussed influence of fluorescense radiation and energy transfer efficiency caused by matrix and environment temperature, searching a favorite condition to achieve higher energy transfer and fluorescence efficiency.