| Since the ultra-broadband NIR luminescent performance of bismuth-doped glass was found, it has received extensive attention and provides a possibility to be utilized for an ultra-broadband optical fiber amplifier to overcome the shortage of gain bandwidth of rare earth doped fiber amplifier, which would realize the large capacity transmission with optical fiber communication system.The research of bismuth-doped glass was mainly focused on improving its performance and exploring the NIR emission mechanism and so on. The preparation method of bismuth-doped glass is one of the significant factors affecting its performance. Bismuth-doped silica glasses are usually prepared by the melt-quenching method which needs high melting temperature and long melting time. It is very adverse to the preparation of bismuth-doped glass due to the volatile of bismuth oxide. Thus, we propose a new manufacture process to prepare the bismuth-doped silica glass.In this paper, bismuth-doped silica glasses were prepared by spark plasma sintering(SPS) using porous materials as raw materials. Compared with the ordinary powder materials, porous materials possess high sintering activity owing to their large specific surface area, which would facilitate the sintering process. Spark plasma sintering has the advantages of fast heating rate, short sintering time and possibility to forward pressure during the sintering process, etc. We successfully explored a novel approach for rapid fabrication of transparent silica glass at low temperature using porous materials and SPS technology together. This method is very favorable for the preparation of bismuth-doped silica glass.Firstly, the transition between transparent and opaque of as-sintered zeolite samples was employed to study the temperature distribution of non-conducting samples during SPS process and the thermal analysis in the finite element code ANSYS was employed to estimate the temperature gradient. Secondly, the silica glasses were prepared by SPS using ZSM-5 and mesoporous material SBA-15. The order-disorder transition of zeolites was studied systematically using the samples prepared at different conditions. The structural changes of samples during the order-disorder transition were characterized by Raman spectroscopy, FT-IR and synchrotron radiation. The influences of the structure changes on the transmittance, luminescent performance and mechanical properties of samples were also studied. The silica glass was prepared by SPS using a mesoporous material SBA-15, and the performances of as-sintered samples were studied. Thirdly, ZSM-5 powders co-doped by bismuth and aluminum were prepared by volumetric impregnation method, and the bismuth-doped zeolite-derived silica glasses were prepared by SPS using these powders. The effects of bismuth and aluminium ions concentration on the luminescence properties of bismuth-doped zeolite-derived silica glass were studied systematically. The influences of the different excitation wavelengths on the NIR luminescent properties were studied and the near infrared luminescent mechanism of bismuth-doped silica glass was also discussed in this paper. Fourthly, Bi doped or Bi/Al co-doped SBA-15 powders were prepared by different powder preparation methods and the Bi doped or Bi/Al co-doped SBA-15 glasses were obtained by SPS. The influences of different powder preparation methods on the colors and luminescent properties of as-sintered samples were studied systematically. The mainly results and conclusions of this paper are as follows:(1) The transition between transparent and opaque of as-sintered zeolite samples was used to illuminate the temperature distribution of the SPS process. The results showed that temperature gradients existed in both radial and axial directions. The sample sintered at 1325℃ was transparent in the center and opaque in the edge, which indicated that the radial temperature gradient existed in this sample and the temperature of the center was higher than the edge. The simulation result by ANSYS showed that the temperature differential was about 26℃ between the center and the edge of the sample. The axial temperature gradient was observed in the specimen obtained at 1315℃. The transparent part of the upper surface was larger than the lower surface in the sample, which suggested that the temperature of the upper surface was higher than the lower surface and it was about 5℃ difference between these two surfaces.(2) The transparent glass samples were successfully prepared by SPS using microporous material ZSM-5 and mesoporous material SBA-15. A series of zeolite-derived silica glasses have been successfully fabricated by SPS. The transmittance of this series zeolite-derived silica glasses increased with the sintering temperature increasing. The transmittance of the sample prepared at 1300°C was lower than 5%. The completely transparent samples could be obtained when the sintering temperature was above 1350°C. The transmittance was the maximum and it was higher than 80% in the range of 780~1700nm and 60% in the UV-vis range of 250~780nm. One absorption band at 300 nm can also be observed in the spectra. The photoluminescence intensity decreased with increasing sintering temperature. The results of synchrotron radiation X-ray diffractions and TEM showed that a few crystallite fragments of ZSM-5 still existed even in a completely transparent sample. And it would produce defects. The samples of ZSM-5 would possess absorption and emission due to the defects. A completely transparent sample can be obtained at 1050℃ using SBA-15 as the raw material. The transmittance of the sample can reach close to 90% in the UV-vis region. The value was nearly consistent with that of the silica glass prepared by traditional melt-quenching method, and it was better than that of silica glasses prepared by ZSM-5, Si O2 nanoparticles or amorphous Si O2.(3) The bismuth-doped zeolite-derived silica glasses with broadband near-infrared photoluminescence have been successfully prepared by SPS. The influence of bismuth ion doping concentration for the luminous performance of bismuth-doped zeolite-derived glass was very complex. When the aluminium content was small, the near-infrared fluorescence can be observed when the samples excited with 500 and 700 nm. But the samples didn’t show any NIR emission when excited by 800 nm. When the aluminum content was high, the near-infrared emission can be observed under the 500, 700 and 800 nm excitation, but the changing rule of the luminous intensity was different. The NIR photoluminescence intensity showed the same changing trend when excited with 500 and 700 nm, but the changing tendency was different from that excited with 800 nm. Aluminum ion had a significant impact on the performance of bismuth-doped zeolite-derived glass. The color of as-sintered samples would become darker gradually with the increase of aluminum ion concentration. The near infrared luminous intensity excited with 500, 700 and 800 nm would increase when the aluminum ion content doped at a certain range, but the content of aluminum ion was different. The maximum NIR emission intensity excited with 500 and 700 nm can be reached when Bi:Al=1:3, and that excited with 800 nm can be reached when Bi:Al=1:9. Interestingly, a broadband NIR emission peaked at 1207 nm with a full width at half maximum of 273 nm was observed when excited with 600 nm, whose intensity was stronger than that excited with 800 nm. On the basis of our research, we suggest that the emissions centered at about 1140, 1240 and 1440 nm can be ascribed to 3P1→3P0 transition of Bi+, 2D3/2→4S3/2 transition of Bi0 and →3Π2g transition of(Bi2)2-, respectively.(4) Bi doped and Bi/Al co-doped SBA-15 powders were prepared by different powder preparation methods, and the Bi doped and Bi/Al co-doped SBA-15 glasses were obtained successfully by SPS. Bismuth-doped SBA-15 glass didn’t show any near infrared emission when excited with 500, 700 and 800 nm. Aluminium ions were indispensable for the near infrared luminescent of bismuth-doped glass. The color of the Bi/Al co-doped silica glasses prepared by equal volume impregnation approach were grayish black and it would be darker gradually with bismuth-doped concentration increasing. The NIR emission can be observed when excited with 500 and 700 nm. But no emission can be found under the 800 nm excitation. The color and luminescence properties of the samples prepared by dilution with ball grinding were in concordance with those of samples prepared by equal volume impregnation approach. The color of 0.10mol% sample prepared by hydrothermal synthesis method was grayish black and XRD pattern showed that bismuth metal existed in this sample. The color would turn red when the bismuth-doping concentration was more than 0.30mol%. And it would be darker gradually with the increase of bismuth concentration. The stronger NIR emission of red samples can be observed when excited with 500, 700 and 800 nm and the luminous performance of grayish black sample was very poor. Compared with bismuth-doped zeolite-derived sample, the emission peaks of 0.90mol% sample excited by different excitation wavelength had a certain degree of red shift. The FWHMs became more concentrated and were almost about 230 or 240 nm. The reason of the grayish black sample may be ascribed to the effect of bismuth oxide decomposition, the silicon hydroxyl of SBA-15 surface, the sintering mechanism of powders, or these factors worked together. |
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