Optimization Of Doping Amount Of Rare Earth Ions In High Silica Glass And Its Luminescence Properties

As the new generation of green light source, power white LED has eliminated incandescent lamp, replaced fluorescent lamp and fully entered the field of general lighting.But because of its working principle of LED chip and yellow phosphor, there are still some problems including poor thermal stability of phosphors and patent barriers, which become one of the bottlenecks limiting the whole LED industry development. Compared with the phosphor materials, rare earth ions doped high silica glasses have higher thermal stability and chemical stability. The package structure of flip ultraviolet LED chip and high silica glass can break package barriers and emitevenly distributed white light. Because of approximate composition between high silica glass and quartz glass, rare earth ions doped high silica glass can beused in the preparation of special optical fiber. However, to satisfy practical application requirements, there are demands of improving luminescent intensities of rare earth ions doped high silica glasses.Luminous intensities of rare earth ions doped high silica glass is mainly influenced by the doping amount of rare earth ions. Before concentration quenching, the luminescent intensity of high silica glass is stronger with the increase of rare earth ions doping amount, but the luminescent intensity of high silica glass will decrease after concentration quenching. So, it is necessary to optimize the doping amount of rare earth ions to improve the luminous intensity of high silica glass. Researchers studied the optimization of rare earth ions doping amount emphatically by the experimental method.Without quantitative analysis theory, the optimal doping amount of rare earth ions can be obtained by a series of experiments, such asadjustments of process parameters, preparations of glass samples, testes of emission spectra and so on.To optimize the doping amountof rare earth ions in high silica glass, focused on above problems, the main contents are stated in detail as following.In order to quantify the doping amount of rare earth ions in high silica glass, the mechanisms of rare earth ions adsorbed on the surface and diffusing in pores were analyzed. The driving force of surface adsorption is ion exchange between hydroxyl groups on the surface of porous glass and rare earth ions, and the driving force of diffusion in pores is the concentration gradient of rare earth ions. The doping amount of rare earth ions in high silica glass is the summation of adsorption amount on the surface and diffusion fluxes in pores. Combined with conservation of mass, the theoretical models of rare earth ions doping amount have been established and the doping amount of rare earth ions has been analyzed,quantitatively.②In order to improve the doping amount of rare earth ions in high silica glass, the theoretical model of doping amount of rare earth ions has been established. The influence factors of concentration distribution of rare earth ions in porous glass, pore diffusion flux, adsorption quantity on the surface and doping amounts have been simulated. The results show that the doping time of rare earth ions is mainly determined by the thickness of porous glass. When the doping time is long enough, the influence factors followed by descending order are doping solution concentrations, pore volumes of porous glass and surface areas. So raising the doping solution concentration is the easiest way to impove the doping amount of rare earth ions in high silica glass.③In order to verify the theoretical model of doping amount of rare earth ions and its influence factors, glass samples with different rare earth ions doping amounts have been prepared by adjusting solution concentrations doping times, parameters of porous glass and Al3+concentrations. Absorbance of glass samples was tested by ultraviolet and visible spectrophotometer to verify the correctness of theoretical model, qualitatively. The results show that the doping amount of rare earth ions can be significantly impoved with the growing of solution concentrations and fractionally impoved with the increasing of pore volumes and doping times. In addition, the co-doped Al3+can significantly reduce the doping amount of rare earth ions.④In order to optimize the doping amount of rare earth ions in high silica glass, the influence factors of luminescent intensity has been studied. The results show that when the sintering parameters of porous glass are consistent, the luminous intensities high silica glasses are only concerned with the doping amount of rare earth ions. Take Ce3+doped high silica glass as an example, when the emitting light of Ce3+ is at shorter wavelength 390 nm, its optimal doping amountis about 1.6807×10-6mol/g~1.7812×10-6mol/g. When the emitting light of Ce3+ is at longer wavelength 418 nm, its optimal doping amountis about 5.2742×10-6mol/g. Besides, a small amount of co-doped Al3+ can significantly improve the luminescent intensity of Ce3+ doped high silica glass.⑤For the application of white LED, high silica glass samples doped with different proportions of Eu2+/Dy3+ and Ce3+/Dy3+ were prepared and the energy transfer process between these two ions were analyzed. The results show that Eu2+/Dy3+ co-doped high silica glass can’t emit white light due to the energy transfer from Dy3+ to Eu2+ and Ce3+/Dy3+ co-doped high silica glass can emit near white light because of the energy transfer from Ce3+ to Dy3+. Take Ce3+/Dy3+ co-doped glass sample as an example, the emission spectra of glass samples excited by LED chips were simulated according to the measurements of fluorospectro photometer. The results show that when Ce3+/Dy3+ co-doped high silica glassesareused for white LEDs, the center wavelength and bandwidth of LED chips should be chosen in an appropriate scope to ensure the stability of emitting light colors.