Ion Co-doped Rare Earth Doped Nanocrystals Fluorescence Effect

Rare earth doped Nanocrystal is a newly developed luminescent material that has both advantangeous of nanocrystal and rare earth (RE) ions. In cureent thesis, Eu3+/ Tm3+:LaF3/LaOF and Eu3+(Pr3+) doped LaF3 or LaOF nanocrystals are prepared by hydrothermal method. The spectroscopic properties of luminescence emission from RE doped- nanocrystals are investigated by laser spectroscopic methods. The influences of nanocrystal matrix, local environment and energy structure of doped ions on the fluorescence emission are studied experimentally. There are three parts included in the thesis. In the first part, we mainly introduce the preparation of core doped LaF3 and LaOF nanocrystals with hydrothermal method and hydrothermal-sintering method. In the second part, we discuss the symmetry and local environment change of nanocrystals caused by the dopping process. The enhancement effects of codoped Tm3+ ions to doped Eu3+ ions in LaF3 anf LaOF nanocrystals are studied. In the third part, we discuss the dependence of fluorescence emission on the mateix change and ions-doping based on energy configuration of doped ions and the symmetry change of nanocrystal matrix.Part one:Synthesis and characterization of tetragonal LaOF:Eu3+/Tm3+, LaOF:Eu3+, LaOF:Pr3 and LaOF:Eu3+/Pr3+ nanocrystals prepared with hydrothermal-sintering methodTetragonal LaOF:Ln3+ nanocrystals are successfully prepared with hydrothermal-sintering method that is simple and can be conducted at easier synthesizing conditions. It is found that in the tetragonal LaOF:(1.0 mol%)Eu3+/Tm3+, the strongest fluorescence emission from Eu3+ is obtained when the comcentration of codoped Tm3+ ion is 0.5 mol%.Part two:Influence of the local environment and symmetry change on the fluorescence emission of Eu3+ in LaOF:Eu3+/Tm3+ nanocrystalsThe optical transitions of Eu3+ in LaOF:Eu3+ and LaOF:Eu3+/Tm3+ nanocrystals with tetragonal crystal structures are studied with laser spectroscopic mehod. fluorescence emissions from 5D1 and 5D0 two excited states are observed when the samples are excited with 532 nm continuous and pulsed lasers. It is found that the intensity of red fluorescence emission, which resulted from the 5D0â†'7F2 forced electric-dipole transition, is obviously stronger in co-doped nanocrystal than that in the singled-coped nanocrystal. The reason is that Tm3+ substitute partial Eu3+ and La3+ in the LaOF nanocrystals so as to band length of some directions in Eu3+ nearby, at the same times, interionic reciprocity have changed from La3+ and Eu3+ to La3+,Eu3+ and Tm3+, the changes increased on the unsymmetry of local environment of Eu3+ and removed f-f forbidden transition thus the red fluorescence emission of Eu3+ in the LaOF:Eu3+/Tm3+ namocrystals was increased.Part three: Dependence of matrix structure and excition wavelength to the fluorescence emission of Ln3+: LaF3/LaOF(Ln3+= Eu3+, Pr3*, Tm3+) nanocrystalsThe change of matrix structure provids different local environment for doped ions, thus provided conditions for changing fluorescence emission properties of doped RE ions. The influence of matrix structure change on the fluorescence emission properties of Eu3+, Pr3+ and Tm3+ coped and codoped fluoride namocrystals are studied with laser excitations of 532 nm,442 nm and 355 nm. Based on the energy structure of doped ions and symmetry change of matrix, we have studied the experimental observations and fluorescence emission properties.The results shows that when Pr3+ and Tm3+ are coped to Eu3+ doped namocrystals, the intensity of red fluorescence emission and its colour purity can be improved significantly.