Synthesis, Characterization And Luminescence Properties Of Oxysulfide Phosphors Doped With Rare-Earth Ions

Rare earth oxysulfide is an excellent luminescent materials matrix. In recent years, it has widely application on medicine, lighting, national defense, and many other areas. In this thesis, we study about long afterglow luminescence and up-conversion luminescence of rare earth oxysulfide luminescent materials. The mainly research content and research results can be summarized as follows:1. A Y2O2S:Eu,Mg,Ti material was prepared via a modified sulphide-fusion route. Compared with the traditional solid-state reaction method, the obtained Y2O2S:Eu,Mg,Ti showed smaller, more uniform particles with higher brightness. The afterglow mechanism study indicated that the long-afterglow material is process-dependent and that its performance is determined by recipe, preparation technology and process used. The luminescence centres of Y2O2S:Ti; Y2O2S:Eu,Ti and Y2O2S:Eu,Mg,Ti are Ti4+ions, Ti4++Eu3+ions and Ti4++Eu3+ions, respectively. The afterglow decay curve can not be fitted using the exponential equation or first-, second-, third-order exponential decay multiple equations beyond30min. The afterglow luminescence of the materials resulted from Ti-related defects that make up two new trap levels. Ti doping created numerous harmful companying defects that decrease luminescence efficiency. Doping of Mg2+ions facilitated the introduction of Ti4+ions into the Y2O2S lattice to effectively modulate the depth and concentration of the trap. Doping of Mg2+-Ti4+ion pairs reduced the number of harmful defects through the formation of a compensation-type hetero-valent substitution solid solution that greatly enhance the afterglow performance. Cold isostatic pressing promoted the entry of Ti ions into the Y2O2S crystal lattice and eliminated defects, such as preferred orientation. In addition, cold isostatic pressing is beneficial to the long afterglow of the resulting material at room temperature.2. Y2O2S:Yb,Er presents green upconversion luminescence under980nm excitation. However, it exhibits excellent red emission under1550nm excitation and its upconversion brightness is more than2.0times to that of Y2O3:Yb, Er under 980nm excitation. Its upconversion investigation shows that the strongest NIR peak is situated at1020nm, the second strong peak is red emission centered at690nm, and the third strong peak is green band under1550nm pumping. The red/green fluorescence branching ratio descends with the increase of Er3+ions concentration or exciting power dramatically. Therefore, red and green two-tone upconversion color can be created by1550nm and980nm excitation respectively. Moreover, a very wide range of emission color can be continuously tuned by the combined contribution of changing composition and exciting power. The upconversion mechanism is also discussed.3. Y2O2S:Yb.Er up-conversion luminescent material has been prepared by colloidal processing method. The morphology and structure has been studied further. The sample we prepared were core-shell structure in nanometer order of magnitude. The average particle size is34nm, and the supernate is suspension liquid. The formation of core-shell structure and the suspension reason is also being studied.