Synthesis, Characterization And Luminescence Properties Of Oxide And Oxysulfide Nanocrystals

Because of the mesoscopic effect, nano-materials exhibit lots of unique physical and chemical properties that are different from those of bulk materials. Especially, people have found that the nano-materials possessing unique luminescence properties would have enormous potential application in many new areas and have large values of explotation and application. Therefore, the research of experiment and theory of luminescence nano-materials has become one of the hotspots in the research fields of advanced materials nowadays. This paper mainly researched on the synthesis and luminescence property of semi-conductor TiO₂ nanocrystals and Gd₂O₂S:Tb, Y₂O₃:Yb,Er, Y₂O₂S:Yb,Er rare-earth phosphors. The main contents and results are as following:1. The TiO₂ nanocrystals were prepared by the direct precipitation method. At room temperature, the luminescence peaks of surface states that mass materials don't take on are observed at 405, 453, 471 and 530nm for the nano-TiO₂. In addition, the intensity of luminescence peaks presents irregular changes with increasing grain size, i.e., with heat treatment. It may be related to the movement of the defects inside the grains and the number of surface states.2. The Gd₂O₂S:Tb has been considered one of the phosphors that has the most efficiency of the light output from X-ray to visible light. However, the traditional synthesis is solid-state reaction, by which the obtained paticle size is very large, thus grinding is required but generally degrading the luminescent efficiencies. Therefore, this paper explored the new synthesis methods, namely, the emulsion liquid membrane (ELM) and the complex precipitation methods, to synthesize the Gd₂O₂S:Tb X-ray phosphor nano-particles. The samples were characterized by XRD, SEM, TEM, PL, XL, FT-IR. The results show the pure Gd₂O₂S:Tb with the hexagonal structure are obtained by these two methods, and the grain sizes are both in the nano-scale. Especially, the complex precipitation method, making use of the reaction principle of the homogeneous precipitation method, has controlled the agglomerate size even in the nano-scale, which has the significant meaning in the enhancement of the resolving power of imagingsystem. Meanwhile, observed a new phenomenone, the energy transfer of the D3—- D4 didn't occure in Gd2O2S:Tb nano-phosphors, and the reason may be that the bottom of the CTS in Gd2C>2S is close to the D3 level, and the energy transfer is much easier to occur between them, thus consequently leading to the probability of the energy transfer of 5D3^<sup>5D4 being lowered greatly.3. On the basement of successful synthesis of Gd2C>2S:Tb x-ray phosphors, complex precipitation method is expanded and applied to synthesis the Y2O3:Yb,Er and Y2O2S:Yb,Er up-conversion phosphor nano-particles, moreover compare the two PL spectra and dicusse the influence of different host on the up-conversion luminescence property. Besides, the properties of up-conversion luminescence and energy transfer processes are studied in details for the different concentration of Yb3+ in Er3+ doped Y2O3 nanocrystals.