| Rare earth (RE) doped nanocrystal as one kind of unique luminescence material has been widely used in all related fields in recent years. Special level structure of RE ions and rich fluorescence radiation make this material show excellent optical properties, thus numerous researchers pay close attention to it. It has been reported that this material can be obtained by kinds of preparation methods including chemical precipitation, hydrothermal method and high-temperature solid-state method, etc. Optical performance of rare earth doped nanocrystal is analyzed mainly by using the as-obtained time domain and frequency domain spectra. In current thesis, the LaOF:Eu3+ nanocrystals have been successfully synthesized by three different methods including hydrothermal, solvothermal and chemical precipitation methods. The samples were characterized by means of XRD and TEM. Various factors that have influence on fluorescence properties were studied by laser spectroscopy method. Four parts are included in the thesis. In the first part, the LaOF:Eu3+ nanocrystals having excellent fluorescence properties were successfully synthesized by chemical precipitation methods, and it was emphasized that red fluorescent radiation of the samples was influenced by annealing temperature, time, doped concentration, content of hydrogen peroxide (H2O2) and the mol ratio of La3+ ion and F- ion. In the second and third part, The LaOF:EuJ+ nanocrystals have been successfully synthesized by hydrothermal and solvothermal methods. Relevant factors influencing the luminous efficiency were analyzed reasonably, including crystal structure and parameters of host lattices. In the last part, we discussed the influence of manufacture technology on average size of nanocrystals, doped concentration, surface modification, local environment, fluorescence emission and fluorescence lifetime, etc.Part one:Chemical precipitation method for synthesis of LaOF:Eu3+ nanocrystals having excellent fluorescent propertyThe LaOF nanocrystal obtained by original chemical precipitation method is mainly be used as a kind of catalyst. Firstly, tetragonal phase LaOF:Eu3+ nanocrystal is obtained through this method. Secondly, rhombohedral LaOF:Eu3+ nanocrystal is obtained through changing the mol ratio of La'+ ion and F- ion. Finally, it is emphasized that red fluorescent radiation of the samples is influenced by reaction temperature, time, doped concentration and content of hydrogen peroxide (H2O2). Red fluorescence emission of tetragonal phase LaOF:Eu3+ nanocrystal obtained in our experiment conditions of doped concentration for 9.0 mol%, temperature in 650℃and content of hydrogen peroxide for 50ml is the strongest. Part two and three:Hydrothermal and solvothermal methods for synthesis of LaOF:Eu3+ nanocrystals having excellent fluorescent propertyIt was found that the dispersion of tetragonal phase LaOF:Eu3+ nanocrystal originally obtained by the hydrothermal and solvothermal method was bad because of higher annealing temperature. Cubic and tetragonal LaOF:Eu3+ nanocrystals having excellent fluorescence emission have been successfully synthesized by hydrothermal and solvothermal methods by reducing the annealing temperature (from 800℃to 460℃) and improving related experimental conditions. Red fluorescence emission intensity of tetragonal LaOF:Eu3+ nanocrystals is stronger than that of cubic phase LaOF:Eu3+ nanocrystals. The main reason of is anisotropy of tetragonal phase LaOF is higher than that for cubic phase LaOF:Eu3+ nanocrystals, which cause the increase of radiative transition rate for the 5D0â†'7F2 transition. We have also obtained two kinds of tetragonal phase LaOF:Eu3+ nanocrystals, the PDF Card numbers are 05-0470 and 44-0121. The observed differences for luminescence intensity in the two kinds of samples are explained by crystallization degree, actual doped concentration and different particle size. Research results show the sample for the card number of 44-0121 has bigger actual doped concentration, poorer crystallization degree and smaller particle, which caused the stronger emission intensity.Part four:The influence of synthesizing processes on tetragonal LaOF:Eu3+ nanoparticlesThe tetragonal LaOF:Eu3+ nanoparticles have been successfully synthesized by three different methods including hydrothermal, solvothermal and chemical precipitation methods. It is found that the particle size, crystal structure, local environment, fluorescence emission and fluorescence lifetime could be adjusted by different preparation steps. Research results show that under the proper conditions, the sample synthesized via chemical precipitation method present the smallest particle size, the shortest fluorescence lifetime and the strongest fluorescence emission. The sample synthesized via solvothermal method present the weakest fluorescence emission. It is also found that the dispersion of the particles obtained by the hydrothermal and solvothermal method is better. In these three kinds of synthetic processes, the dependence of luminescence intensity on the doped concentration is the same. The doped concentration for the strongest red fluorescence intensity is about 9.0 mol%. |
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