Study On The Photoluminescense Properties Of Li～+/Ag～+ Doped Gd₂O₃: Sm Nanocrystals

Nanoscale phosphors has unique advantages in improving the spatial resolution of display unites, however, due to quenching effect of nanoparticle surface state, the luminescent efficiency tends to decrease as the particle size decreasing. It was found that some ions as coactivators, even in very small quantities, could play an important role in the enhancement of the luminescent efficiency of phosphors. In this thesis, we make a comprehensive study of the structural, morphological and luminescent properties of Li⁺/Ag⁺ doped Gd₂O₃: Sm nanocrystals, by using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and fluorescence spectrophotometry to give some explanations of the enhanced photoluminescence. The main contents and the important results are listed as followings:1. Nanocrystals Gd₂O₃: Sm were prepared by chemical self-combustion. The mean grain size of the materials ranges from 10nm to 50nm by controlling the reaction concentration and annealing temperature.2. When excited at 275 nm and 980 nm, both photoluminescence and upconversion emission of Sm3⁺ can be observed.3. Li⁺-doped Gd₂O₃: Sm nanocrystals were prepared by the combustion method. It was found that the incorporation of Li⁺ ions into the Gd₂O₃: Sm nanocrystals greatly enhanced the photoluminescence intensity of Sm3⁺ ions in both photoluminescence and upconversion emission compared with that of Gd₂O₃: Sm nanocrystals. As we all known that the defects of the surface of the nanoparticles, which provide non-radiation recombination routes for electrons and holes, often act as non-radiative centers and have great influence on luminescent properties. It is suggested that the incorporation of Li⁺ ions can greatly decrease the deficiencies and oxygen vacancies. That is, the defects and oxygen vacancies of the surface of nanoparticles decreased when Li⁺ content was doped, which decreased the luminescence quenching centers, thereby enhanced the emission intensity of Sm3⁺. 4. Ag⁺ doped Gd₂O₃: Sm nanocrystals were prepared by chemical self-combustion. The improvement in photoluminescence with the Ag⁺ doping may result not only from improved crystallinity, but also from the decreases of defects on the surface of the nanoparticals, which act as non-radiative transition probabilities and lead to the luminescent quenching of the nanocrystals.