| The rare earth doped oxyfluoride glass ceramics of 3 ?m mid-infrared band can combine the best spectroscopic properties of rare earth in fluoride nanocrystals and excellent macroscopic properties of oxide glasses(high optical transparency,good chemical stability and thermomechanical properties,adjustable composition and the ability to fabricate optical fibers),which is of great scientific and applied value in the fields of gas monitoring,laser surgery and military.The past two decades have witnessed considerable progress for oxyfluoride glass ceramics in the chemical composition design,crystallization properties,upconversion and infrared emission,and even the prepartion method of glass ceramic fiber.However,there is still a need to make efforts for oxyfluoride glass ceramics in the following aspects:the controlled crystallization mechanism,the broadband 3?m emission mid-infrared spectrum,the mid-infrared emission efficiency,and the varation of energy transition induced by local environment and glass sturcture.This dissertation includes the following seven chapters.In Chapter ?,the applications of 3?m mid-infrared emisssion and rare earth ions doped luminescent materials have been introduced firstly.And the types,features,preparation methods,application and research progress of oxyfluoride glass ceramics have been reviewed.The research progress of enhanced luminescence by Ag nanoparticles have also been presented.Then the research purpose and research content of the dissertation were put forward.In Chapter ?,the technology roadmap and the experimental methods were introduced,including the raw materials and preparation procedures of oxyfluoride glass ceramic,physical,morphological,thermal,structural and spectroscopic properties measurements,and theory analysis for spectroscopic parameters.In Chapter ?,Yb/Ho codoped transparent oxyfluoride glass and glass ceramic have been prepared.Raman spectra indicated the variation of glass structure brought about by the formation of NaYF4 nanocrystals.X-ray diffraction curves and Judd-Ofelt intensity parameters confirmed the incorporation of Ho3+ into NaYF4 nanocrystals.Multi-band emissions including upconversion visible emission,1.2?m,2?m,2.85?m emissions were detected for combined analysis.Significantly enhanced visible upconversion and 2.85 ?m emissions were achieved in glass ceramic under a 980 nm laser diode pumping.A broadband spectrum with a full-width at half-maximum close to 132 nm was obtained.Besides,the calculated peak emission cross section was 0.6×10-20 cm2,suggesting the glass ceramic is a promising gain material that can be applied to broadband amplifiers in mid-infrared region.Furthermore,energy transfer mechanisms in glass and glass ceramic were proposed based on visible to mid-infrared emission spectra.It was found that the change of photon energy environment around rare earth ions induced different dominant transitions in glass and glass ceramic.Finally,the influence of phonon energy on transition processes was further quantitatively investigated,which may provide useful guidance for obtaining highly efficient 2.85 ?m emission of holmium.In Chapter IV,there were two parts.In the first part,a series of oxyfuoride germanosilicate glasses and glass ceramics with different glass former(Si and Ge)were investigated.On one hand,a series of oxyfluoride germanosilicate glasses and glass ceramics with different Si/Ge ratio were prepared for structural analysis.The ability of NaYF4 crystallization in oxyfluoride germanosilicate glass was decreased with Ge content increasing,and its reason may be the strong attraction of Ge4+ to F-as a result of fluoride crystallization with deficient fluorine source.On the other hand,a series of Yb/Ho codoped oxyfluoride germanosilicate glasses and glass ceramics with different Si/Ge ratio were prepared to compare luminescent properties.With the increased of Ge content,the Judd-Ofelt intensity parameter ?2 of Ho3+ in glass was increased,the 2?m emission of glass was decreased,the 2?m emission of glass ceramic was increased at first and decreased afterwards,and the 2.9?m emission of glass ceramic was decreased.In the second part,with the aim of broadband 2.7?m spectrum,Er/Ho codoped oxyfluoride germanosilicate glass and glass ceramic containing NaYF4 NCs were prepared.The structural analysis indicated that the glass network consists of SiO4 and GeO4 structural units,while the network of the glass ceramics consists of SiO4,GeO4 and GeO6 units together with NaYF4 NCs.Therefore,rare earth ions can locate at multiple local structures in oxyfluoride germanosilicate glass ceramics which can creat a range of dipole environments.Broadening of 2 ?m and 2.7 ?m emission spectra together with the change in spectra shape were observed in oxyfluoride germanosilicate glass ceramics.Energy transfer mechanism between Er3+ and Ho3+ and non-resonant energy transfer analysis were conducted to comprehend the change in fluorescence spectra.The results indicate that the reasons for the broadening of 2.7 ?m emission spectra in germanosilicate glass ceramics are:(1)more complicated glass network,(2)energy level splitting of Er3+in crystal field and(3)the enhancement of Ho3+:5I6?5I7 transition in NaYF4 nanocrystals.In Chapter V,novel oxyfluoride borosilicate glasses and glass ceramics containing both Ag nanoparticles and Er doped hexagonal NaYF4 nanocrystals were designed and prepared.Structural analysis indicated that the Ag+concentration can affect the distribution of Na+ ion and bridge oxygen in boron-rich and silicon-rich phases,which induced the transformation between B03 triangles and B04 tetrahedra during crystallization process.In addition,there was a turning point when the doped Ag+ions concentration reached its solubility in borosilicate glass.Besides,the influence of aggregated Ag nanoparticles on 2.7 ?m emission was studied,and its origin was revealed by qualitative and quantitative analysis of the Er3+-Ag nanoparticles(Localized field enhancement effect)and Er3+-Er3+(energy transfer)interactions within glass and glass ceramic.Furthermore,the high lifetime of 4I11/2 level(2.12ms)and peak emission cross section in 2.7 ?m(6.8×10-21 cm2)of glass ceramic suggested the prepared glass ceramics have promising mid-infrared laser applications.Moreover,the 2.7 ?m fluorescent enhancement was more obvious in glass than in glass ceramic,which is found to be related to the size of Ag nanoparticles and the distance between Ag nanoparticles and Er3+ ions.In Chapter VI,inspired by the core-shell nanocrystals structure,core-shell like nanoarchitecture was constructed in Yb/Er ions and Yb/Ho SrTi03 NCs-codoped TZNB glass to prepared novel core-shell like glass ceramic.Designed spectroscopic experiments demonstrated that the adverse energy transfer between Er3+ ions in glass region and Ho3+ ions in crystal region was effectively prohibited,which permits the highly efficient emissions of Er3+ and Ho3+ ions independently.Luminescent properties of rare earth ions in glass,nanocrystals and nanocrystals doped glass were compared.Furthermore,energy transfer mechanism in Yb/Er ions and Yb/Ho NCs-codoped TZNB glass was proposed.Finally,all results of this disseration have been concluded in Chapter VII.Besides,it pointed out some shortcomings and gave some advice on future works. |
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