Synthesis, Characterization And Properties Of Silicate-based Phosphors

Afterglow phosphor is a kind of photoluminescence material which can absorb the excitation energy and slowly release the visible light after shutting down the stimulate source. Because of its unique chemical and physical characteristics, afterglow phosphor has an unexpectedly large field of applications, such as safety exigence, transportation, building anddecorating...... Recently, silicate-based phosphor attracted much attention and became aninteresting topic in the field of afterglow luminescent materials because of their excellent chemical and physical properties and UV radiation resistance. However, compared with aluminate phosphor, silicate phosphor has relatively poor performance in luminescence efficiency and afterglow characteristic. It is necessary to study the relationship between the crystal structure and luminescence properties of silicate-based phosphor to further enhance its luminescent properties. Also, its synthetic route is the traditional solid-state reaction. The shortcomings of this approach are the need for high-temperature and long-time calcination. The unreacted phases appeared easily which reduced greatly its luminescent brightness and afterglow characteristic. Therefore, wet chemical approach to prepare silicate-based phosphor semms to be an attractive alternative. Especially in recent years, well-control over phosphor's particle size and morphology to improve its luminescnt performance through the wet chemical approach became the goal of researchers' studies. Meanwhile, because of its moderate synthetic conditions and controllable luminescence scope, non-metallic ions activated silicate-based phosphor has attracted people's great interest. In the dissertation, with the recently development in synthetic technology and phosphor formation mechanism, we hope to overcome the above motioned question, develop effective silicate phosphor synthesis method, and improve the luminescent properties and morphology control of silicate phosphor. XRD, PL, FT-IR, TG-DTG, TEM, and SEM adsorption were used to characterize the silicate phsophor. The results are listed below:1. The relationship between the crystal structure and luminescence properties of silicate-based phosphor was systematic studied to further enhance its luminescent properties. The results showed that different ratio of SrO to SiO₂ in matrix lattice resulted in the variations of emission spectrum and intensity; Because of relatively lower concentration,trap density and depth of luminescence center Eu²⁺, luminescence intensity and afterglow performance is poorer in rich-Sr crystal phase; RE³⁺ (RE = Ce, Nd, Gd) as a co-doping rare earth ions has positive impact on the various aspects of phosphor performance and the persistent energy transfer from RE³⁺ to Eu²⁺ is the key to explain this phenomenon.2. Different wet chemical synthesis ways were applied to improve all aspects of alkine earth silicate phosphors' performance. Long afterglow silicate phosphor which prepared by nano-coating method have better luminescence intensity and afterglow characteristic. Its precursor particles had core-shell structure and quasi-spherical morphology. This particular precursor's structure has great influence on the phosphor's performance in all aspects. Long afterglow silicate phosphor was also prepared by (aminopropyl)-triethoxysilane (APTES) co-precipitation method. Effects of synthetic temperature on the crystal characteristics, luminescent properties and afterglow performance of phosphors have been discussed in detail.3. By using modified sol-gel method, micron-size spherical Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺ and Sr₃MgSi₂O₈:Eu²⁺, Dy³⁺ phosphor were obtained. With increasing the volume of ammonia in the preparation of the precursor, the phosphor's particle size can be controlled to some extent. Further insceasing the ratio, it can be realized from Sr₂MgSi₂O₇ to Sr₃MgSi₂O₈ matrix lattice changes, which caused a series of changes in spectral properties and decay curves of as-synthesized phosphors.4. Rare earth activated silicate aluminate phosphor SrAl₂Si₂O₈:Eu²⁺,Dy³⁺ and Sr₂Al₂SiO₇: Ce³⁺,Tb³⁺ were prepared by the alkoxide sol-gel method. The resluts showed that phosphor prepared by alkoxide sol-gel method can provide more luminescent intensity and better afterglow characteristic compared with the same phosphor prepared by solid-state method. Especially for Sr₂Al₂SiO₇:Ce³⁺,Tb³⁺ white phosphor, the emission spectra of the samples with different doping concentrations showed that the Tb³⁺ emission was dominant because of the persistent energy transfer from Ce³⁺.5. Non-metallic ions activation amorphous silicon dioxide luminescent sphere were also studied in this thesis. A new class of monodisperse, luminescent silica spheres were produced upon calcination of hybrid amine-functionalized silica spheres. Silica microcapsules (hollow spheres) were synthesized successfully by combination of CTAB- stabilized water/oil emulsion system with mediated hydrothermal method. More importantly, it is also observed that under ultraviolet light excitation such a hollow core-shell structure spheres would emit blue light.