The Key Technology Of Preparation Of Rare Earth Ions Doped High Silica Glass And Its Influence To Luminescence Properties

Nowadays, some important problems, including poor thermal stability of usual YAG yellow phosphor and patent barriers of blue LED chip and yellow phosphor package structure, are main obstacles of high power white LEDs’ further large scale application. Because of high thermal stability and chemical stability, unease to concentration quench, easy to break package barriers, rare earth ions doped high silica glass have been extensive concerned and researched. However, to satisfy white LEDs’ practical application requirment, there is an improve demand for luminescence related properties, including refractive index, relative density, chromaticity coordinates, quantum efficiency, luminescence intensity, of rare earth ions doped high silica glass.Preparation process of rare earth ions doped high silica glass can be divided into three main procedures: nanoporous glass preparation, rare earth ions adsorption, sintering. The main effects of nanoporous glass preparation are refractive index, quantum efficiency and luminescence intensity; The main effects of rare earth ions adsorption are chromaticity coordinates, quantum efficiency and luminescence intensity; while the main effects of sintering process are relative density, quantum efficiency. And the luminescence properties of high silica fluorescence glass are closely related to its critical preparation parameters and key technologies. Researchers emphatically studied the preparation parameters which are directly, significantly related to luminescence properties of high silica glass, such as luminescence intensity and quantum efficiency, and have achieved much progre ss. Comparatively speaking, the researches including the influence of nanoporous glass preparation parameters on luminescnece intensity, the influence of rare earth ions adsorption parameters on chromaticity coordinate, the influence of sintering parameters on relative density, and the influence of sintering parameters on fluorescence lifetime which are not very significant related to luminescence properties are comparative weak, and rare reports are published.To improve the luminescence related properties of rare earth ions doped high silica glass, focused on above four key problems, the dissertation researches on critical preparation parameters optimization. The main contents are stated in detail as following.â‘  According to surface properties of nanopore wall and rare earth hydrated molecules in solution, multilayer adsortion mechanism of nanoporous glass to rare earth ions was analyzed, and it was concluded that by the premise of no concentraction quenching occures, the larger the pore volume of nanoporous glass, the larger the adsorption capacity, the higher the luminescence intensity of high silica luminescence glass. By the premise of compositions of nanoporous glass is close to that of quartz glass, the critical parameters including phase separation temperature, phase separation times, acid solution concentration, ultrasonic cleaning, pore expansion were optimized. The relation of pore volume and luminescence intensity was verified at last.â‘¡ For the demand of chromaticity coordinate of white light or near white light, the optimal species and concentration of rare earth ions in soulution were researched and presented. Through the analysis of energy level transitions and emission colors of visible light emitted rare earth ions, the doping combination of Eu2+/Dy3+ and Ce3+/Dy3+ were selected. By comparison of emission spectra of single doped and co-doped high silica luminescence glass, the Eu2+â†'Dy3+ and Ce3+â†'Dy3+ energy transfer process were verified in high silica luminescence glass. By varying the Dy3+ concentration in solution, the ratios of blue and yellow propotion of emission spectra were varied; By comparison the chromaticity coordinate calculation of corresponding high silica luminescence glasses, the critical parameters including species and concentrations of rare earth ions in solution were optimized. The optimization results showed that the doping combination of Eu2+/Dy3+ could not generate near white light emitting; while the Ce3+/Dy3+ one could emit near white light; The optimal concentration of Ce3+ in solution was 0.02mol/L, while the Dy3+ was 0.10mol/L.â‘¢ The influence of sintering parameters on relative density of high silica glass was discussed, and the optimal values of sintering parameters were obtained. On basis of the frenkel principle of viscous sintering, by analysis of structural characteristics’ evolution during sintering process, taking whether the pores were interconnecting as judgement, the sintering process was divided into earlier stage and later stage which were described by interconnecting cylinders and closed spherical shell respectively. By introducing kronecker symbol to integrate nonisothermal and isothermal sintering situations, the sintering kinetics of nanoporous glass was established. The influence of sintering temperature, holding time and heating rate on relative density were respectively discussed. Furthermore, for relative density optimization, the sintering parameters’ consideration order of sintering temperature, houlding time, heating rate are established.â‘£ Based on theory of reaction kinetics, by the premise of hypothesis of reaction mechanism function, residual fraction of hydroxy after nonisothermal and isothermal sintering were derived, and the residual fraction of hydroxy based on normal sintering curve was obtained. Combined with Forster-Dexter model, the theory model between fluorescence lifetime of rare earth ions and sintering parameters was established. The influences of sintering temperature, holding time and heating rate on fluorescence lifetime were respectively discussed, which revealed the influence degree of sintering parameters to fluorescence lifetime,and give the selective order of sintering parameters: sintering temperature, holding time, heating rate. Take Sm3+ doped high silica luminescence glass as example, the hypothesis of reaction mechanism function was verified, and the concrete expression of fluorescence lifetime of Sm3+ was obtained. The optimal values or selection principles of critical sintering parameters were presented based on fluorescence lifetime expression, and the final optimal values or selection principles which aimed to demands both of relative density and fluorescence lifetime were obtained.