Compositional Design Of Silica-germanate Glasses And Near Infrared Luminescence Properties Of Bi Ions

The birth and development of optical fiber communication is an important revolution in the history of telecommunications.With the development of research,the emergence of optical fiber amplifiers reduces the loss of optical signals in optical fiber transmission and widens the output bandwidth of optical fibers.Its emergence has brought a new level for optical communication.The traditional Erbium Doped Fiber Amplifier?EDFA?has a small coupling loss between the main fiber itself and the line fiber,leading to that the signal can be transmitted more completely during the transmission process.However,the difference in energy levels between the Er³⁺ion levels determines that the operating wavelength of the EDFA is fixed and limits the amplification wavelength.Moreover,the gain bandwidth of EDFA is only about 40nm,which greatly limits the development of EDFA.Therefore,in recent years,a large amount of research has focused on the exploration of variable-valent metal ions doped fiber amplifiers.Bi ions not only have the broadband emission performance in the near-infrared band,but also the multi-valent Bi ions are prone to lose electrons because their outermost electrons are not full of shells.Therefore,Bi ions are extremely sensitive to the surrounding environment of the matrix,resulting in the variable and controllable valence states.Meanwhile,the hypersensitive feature on the glass host leads to the effect of network formers and modifiers in different kinds of glass component is uncertain.Hence,this project aims to enhance the near-infrared fluorescence performance of Bi ions by tailoring the network structure and optimizing the network formation and network intermediates in the glass components on the basis of the most basic glass matrix.At the same time,this project explores the Bi-related near-infrared emission center and obtains ultra-wideband near-infrared emission by co-doping the glass sample with Bi ions and rare earth ions.This dissertation mainly includes the following five chapters.The first chapter summarized the development and classification of fiber amplifiers.It focused on the luminescence mechanism of Bi-doped materials for fiber amplifiers and the dominate factors affecting their luminescence properties in different glasses.The research progress of rare earth ions and bismuth co-doped glass materials was introduced.Finally,the research purpose and research content of this dissertation were presented.In chapter 2,the preparation method,performance test method and theoretical calculation and analysis method of glass samples were introduced.The chapter 3 studied the different dominant factors affecting the near-infrared emission properties of Bi ions in different matrix Bi-doped glass samples.The hybrid structure of silica-germanate in which the[GeO₄]and[SiO₄]are connected through a bridge oxygen bond was realized by adjusting the ratio of SiO₂/GeO₂ component in the glass component.The results about XPS and Raman spectroscopy showed that the strength of Ge3d is reduced but the chemical shift of its binding energy is not significantly changed.Hence,the ligancy of Ge⁴⁺does not change when the glass composition changed,that is,most of the Ge⁴⁺ions in the glass network exist in the form of stable[GeO₄]and can be combined with[SiO₄]to form Si-O-Ge structure.Additionally,for glasses consisting of two different glass formers,the glass networks remain virtually dominated by one type of topological structures.The mixed structure effect produced by the silica-germanate hybrid structure enhanced the near-infrared luminescence of Bi,and the silica-germanate glass with[GeO₄]as the dominant structure in the prepared glass samples has the best near-infrared luminescence performance due to the difference in their dominant structure.Meanwhile,in the[GeO₄]dominated silica-germanate glass component,Al³⁺can form AlO₄-tetrahedral by capturing NBO which originates from the hybrid structures and connect the broken glass network.The surrounding environment of Bi NIR centers has been tuned by increasing AlO₄-tetrahedral result in the accelerated diffusion of alkali metals.Therefore,the increased formation of Bi-related near infrared emission centers was conducive to the near infrared emission performance of glass samples.Finally,the related results showed the appropriate use of BaO in the glass component and reduction atmosphere can enhance effectively the near infrared emission performance.The chapter 4 studied the near-infrared fluorescence properties of Bi-doped,Bi/Ho co-doped and Bi/Er co-doped glass samples excited by different pump wavelengths?490,690,808 and 980 nm?.In the energy transfer process,ultra-wideband near-infrared emission spectra are obtained by energy transfer between rare earth ions and Bi ions.In the Bi singly doped glass samples,it was found that the near-infrared emission centers of the Bi ions are composed of two different low valence states of Bi ions?Bi⁰ and Bi⁺?by using excitation spectra of different pump wavelengths and monitoring their excitation spectra.In the Bi/Ho co-doped sample,Bi?Bi⁰?can act as a sensitizer to absorb the pump energy of 808 nm and then the energy was transferred to Ho³⁺:⁵I₆ level,which produces a fluorescence emission of 2000 nm.The results showed that Bi can be used as a non-rare earth sensitizer to sensitize rare earth in addition to the near-infrared emission center.Meanwhile,the near-infrared emission centers?Bi⁰ and Bi⁺?of Bi ions can be excited at the same time under the excitation of 490 nm,and the near-infrared emission from the transition between the two levels overlapped with each other.Hence,Bi/Ho co-doped glass possessed an ultra-wide near-infrared emission peak with a full width at half maximum?FWHM?308nm.The Bi/Er co-doped glass samples compensated for gain unevenness and long-band tailing problems of Bi near infrared emission.When the concentration of Er₂O₃ is in the range of 0.01-0.04 mol%,the increase of Er₂O₃ can enhance the fluorescence emission intensity of Bi ion at around 1290 nm.However,with the further increase of the Er₂O₃ concentration,the energy transfer between Bi and Er ions and the cross-relaxation led to the quenching of the fluorescence intensity of Bi ions.Especially,Bi⁰ and Er³⁺are simultaneously excited by the 808 nm laser sources pumping.The energy transfer process resulted in ultra-wideband near-infrared emission?FWHM:445 nm?owing to the interactions between Bi⁰ and Er³⁺ions.Finally,the chapter 5 of the thesis is the summary part of this thesis.It summarized the experimental results of the full text,and pointed out the shortcomings of this paper and gave some advice for the future works.