Investigation On The Mid-Infrared Emission Properties Of Rare-Earth Ions Doped Silica-Germanate Glass

During the last decade,2³?m solid-state lasers have been a hot research topic for their wide applications in the remote sensing,environmental monitoring,biomedicine and military field.Among all the gain medium,glass fiber has caught people's eyes in academic circles and industry for its excellent performance,meanwhile the gain medium is the core of the laser technology.Glass fiber is mainly composed of rare earth ions and glass matrix.Up to now,Er³⁺?2.7?m?,Ho³⁺?2.9?m,2.0?m?,Tm³⁺?1.8?m?and Dy³⁺?2.9?m?ions are used as common rare earth ions for the 2³?m emission.The glass matrix is as important as the rare earth ions.A suitable host for2³?m fiber laser has three basic requirements:high glass stability,high gain ability and high mechanical strength.Silica-germanate glass which combines the merits of silicate and germanate glasses?larger refractive index,high thermal stability,low phonon energy and high rare earth ions solubility?is a potential material for 2³?m laser.The motivation of this study is to find a promising silica-germanate glass for the 2³?m laser applications.Chapter I has briefly introduced the concept of laser,the rare earth ions used in mid-infrared and the research progress of glass matrix.At last,the purpose and research content of the dissertation were presented.Thesecondchapterintroducedthepreparationmethodsof silica-germanate glasses,including the measurements of the properties and theory analysis.InchapterIII,thesilica-germanateglasses35SiO₂-35GeO₂-20Ga₂O₃-5BaO-5Li₂O?SGGB?have been prepared by using traditional high temperaturemeltingmethod.Atthesametime,thesilicate55SiO₂-5Al₂O₃-20CaO-20Na₂O?SCN?andgermanateglasses75GeO₂-5Ga₂O₃-20BaO?BGG?were prepared as comparative samples.According to the structure,physical and chemical properties analysis,SGGB possesses high thermal stability,moderate phonon energy and high rare earth ions solubility.Firstly,the Tm³⁺doped SCN,BGG and SGGB have been prepared.Based on the measured absorption spectra,the Judd-Ofelt parameters werecalculatedanddiscussed.Theradiativetransition probability(A_rad)of³F₄?³H₆ in SGGB was 308.09s^-1,which was almost twice as much as A_rad(157.53s^-1)of SCN.The 2?m emission intensity of SGGB was twice more than that of SCN and near to the peak intensity of BGG.According to the Fuchbauer-Ladenburg theory,the calculated emission cross section and gain coefficient in SGGB at 2?m were 7.08×10^-21cm² and 3.03cm^-1,which were lager than those of SCN(4.67×10^-21cm²,2.41cm^-1).Then,the influence of Ce³⁺to the 2?m emission spectra of Ho³⁺/Yb³⁺co-doped silica-germanate glasses have been investigated.Under 980nm LD pumping,the maximum value of the 2?m emission intensity has been observed with the concentration of 0.1mol%CeF₃,and the emission cross section and gain coefficient were 4.43×10^-2121 cm² and 1.9cm^-1,respectively.Meanwhile,the energy transfer mechanisms existed in Ho³⁺,Yb³⁺and Ce³⁺ions were investigated based on the measured spectra and the decay profiles.Additionally,the energy transfer microparameters were calculated using F?rster-Dextertheoryandtheenergytransfercoefficientof Yb³⁺:²F_5/2?Ho³⁺:⁵I₆ was as high as 7.54×10^-40cm^-6/s with of 0.1 mol%Ce³⁺addition,which was larger than that in SGGB without Ce³⁺(5.50×10^-40cm^-6/s).All results indicate that the Ce³⁺has positive influence on transfer of Yb³⁺:²F_5/2?Ho³⁺:⁵I₆ in Ho³⁺/Yb³⁺co-doped silica-germanate glass.In chapter IV,the spectroscopic properties of 3?m emission in Ho³⁺/Yb³⁺co-doped silica-germanate glasses and the influence of Sm³⁺have been investigated.Firstly,Ho³⁺/Yb³⁺co-doped silica-germanate glass has been prepared.Based on the measured absorption spectra and Judd-Ofelt theory,the A_radad of ⁵I₆?⁵I₆ in SGGB was 30.27s^-1.Moreover,the measured lifetime and emission cross section at 2.85?m were 283?s and 8.05×10^-21cm²,respectively.Then,the influence of Sm³⁺to the 3?m emission spectra of Ho³⁺/Yb³⁺co-doped silica-germanate glasses have been investigated.Under980nm LD pumping,the maximum value of the 2.85?m emission intensity has been observed with the concentration of 0.3mol%Sm₂O₃,and the emission cross section and gain coefficient were 14.9×10^-21cm²and 6.68cm^-1,respectively.Moreover,the decay profiles of Ho³⁺:⁵I₇ level were measured.It can obtained that the lifetime of Ho³⁺:⁵I₇ level greatly decreases after the introduction of Sm³⁺ions.This process effectively reduced the self-inhibition effect of Ho³⁺:⁵I₆?⁵I₇ transition,which was beneficial for population accumulation of upper level of 2.85?m emissions.Additionally,the energy transfer efficiency???of Ho³⁺:⁵I₇ to Sm³⁺:⁶H_13/23/2 was as high as 65.1%,which confirmed the efficient population inversion of Ho³⁺2.85?m emission.The last chapter is the conclusion.All results of present work have been concluded in this,and mentioned the shortage that should be improved in the next stage.