Investigation On The Mid-Infrared Emission Properties Of Rare-Earth Ions Doped Germanate-Tellurite Glass And Fiber

Recently,2³?m solid-state lasers have drawn considerable attention due to their wide and important applications,including medical treatment,environmental monitoring,military defense,and so on.Er³⁺?2.7?m?,Ho³⁺?2.9?m,2.0?m?,Tm³⁺?1.8?m?and Dy³⁺?2.9?m?ions are common rare earth ions used for the 2³?m emission.Up to now,much work has been done on rare earth?RE?doped materials generated 2?m emission,especially Tm³⁺doped crystal,silica,silicate and heavy-metal-oxide?HMO?glasses.Meanwhile,generating 3?m emissions,previous efforts have mainly been paid to glasses such as fluoride?ZBLAN?,chalcogenide glasses and fibers.Among many alternatives,germanate-tellurite glasses emerge as good mid-infrared fiber laser materials because they combine the various merits of germanate glasses and tellurite glasses(larger refractive index,better chemical stability,a broad transmission window,better mechanical properties and lower phonon energy(700⁹00cm^-1)).The motivation of this study is to find suitable rare-earth ions doped host glasses for 2³?m urtrashort pulse laser.This dissertation includes the following six chapters.The first two chapters are the literature review,experimental methods and theoretical basis.The middle three chapters are core parts of the dissertation.The final chapter?Chapter VI?is the conclusion.Chapter I is literature review.Firstly,the principle of laser generation,developments and applications of laser were proposed.Then,rare earth ions generating 2³?m lasers and hosts materials have been introduced briefly.At last,the purpose of the dissertation was put forward.In chapter II,the experimental methods were introduced,including the preparation procedures of germanate-tellurite glasses,measurements of the physical and spectroscopic properties,and theory analysis.In chapter III,two components of germanate-tellurite glasses have been investigated and prepared by using traditional high temperature melting method.For the two systems,the physical,infrared transimission and thermal performance of glasses were studied.The glasses with the compositions of70Ge O₂-10Te O₂-6K₂O-4KF-5Nb₂O₅-5La₂O₃and10Ge O₂-65Te O₂-10Nb₂O₅-15YF₃ have high temperatures of glass transition?T_g:540°C and 380°C?and good thermal stability??T:190°C and125°C?,respectively.In Chapter IV,Firstly,based on the GTKN system,a series of Tm³⁺doped germanate-tellurite glasses have been prepared.Based on the measured absorption spectra,the Judd-Ofelt parameters were calculated and discussed.And the radiative transition probability and lifetime of ³F₄?³H₆ in 1.0mol%Tm F₃ doped glass are 281.36s^-11 and 4.54ms,respectively.The intensity of2?m emission increased with the Tm³⁺content and the maximum value of the2?m emission intensity can been observed at the concentration of 1.0mol%Tm F₃.According to the Fuchbauer-Ladenburg theory,the calculated peak value of emission cross section at 2?m of Tm³⁺doped sample?GTKNT4?reaches 9.46×10^-21cm².Meanwhile,the positive gain properties proves that it is a typical three-level laser system.Then,the 2?m emission spectra and energy transfer mechanism of Ho³⁺/Yb³⁺codoped germanate-tellurite glasses have been investigated.Efficient 2?m emission of Ho³⁺ions sensitized by Yb³⁺ions from the host glass is observed under 980nm pumping.The maximum value of the 2?m emission intensity has been observed at the concentration of 2.0mol%Yb F₃ codoped with 0.75mol%Ho F₃ and the lifetime is high as 5.47ms.Additionally,the energy transfer microparameters are calculated using F?rster-Dexter theory and the energy transfer coefficient of Yb³⁺:²F_5/2?Ho³⁺:⁵I₆ is high as 8.74×10^-40cm^-6/s.Our results show that Ho³⁺:2?m emission can be sensitized by Yb³⁺efficiently,and Ho³⁺/Yb³⁺codoped GTKN glasses might have potential application in MIR lasers.Another key focus of this chapter is the investigation of 2?m optical properties in RF₃?R=Al,Y and La?modified germanate-tellurite glasses.Based on the GTNY system,the effects of RF₃ on thermal properties such as thermal stability??T?,crystallization activation energy?E_p?in germanate-tellurite glasses were investigated.It is found that the?T and E_p of GTNY sample are up to 137°C and 407k J/mol,respectively,much higher than those of GTNAl and GTNLa samples.For the YF₃ modified Tm³⁺doped germanate-tellurite glass,the emission intensity and cross section at 2?m were higher.Furthermore,the 2?m lifetime of GTNY sample is also higher than those of GTNAl and GTNLa samples.Rusults indicate that this Tm³⁺doped GTNY glass might have potential application in 2.0?m lasers.In the end of this chapter is to investigate the enhanced effect of Er³⁺ions on 2?m emission of Ho³⁺/Yb³⁺codoped germanate-tellurite glass.2?m emission spectra of Ho³⁺/Yb³⁺codoped and Ho³⁺/Er³⁺/Yb³⁺triply doped germanate-tellurite glasses have been studied.2?m emission in Ho³⁺/Er³⁺/Yb³⁺triply doped germanate-tellurite glass pumped by 980nm LD can be greatly enhanced by adding Er³⁺ions simultaneously.Compared with Ho³⁺/Yb³⁺codoped sample?HY?,2?m emission,lifetime and emission cross section of Ho³⁺/Er³⁺/Yb³⁺triply doped glass?HYE0.75?increased all by 1.5times,respectively.Additionally,the energy transfer microparameters are calculated using Forster-Dexter theory and the result shows the energy transfer coefficient from Er³⁺:⁴I_13/2 to Ho³⁺:⁵I₇ can be realized under 980nm LD excitation.In chapter V,spectroscopic properties of 3?m emission in Er³⁺doped germanate-tellurite glasses have been investigated.Firstly,the emission intensity at 2.7?m has been analyzed under the excitation of 980 nm LD.The intensity of 2.7?m is enhanced with the increasing of Er F₃ from 0.5mol%to1.5mol%.The spontaneous radiative rate and branching ratio of 2.7?m are35.57s^-1 and 17.68%,respectively.The calculated peak value of emission cross section at 2708nm is 13.87×10^-21 cm².The energy transfer mechanism and the energy transfer microparameters in Er³⁺doped germanate-tellurite glass has been investigated and calculated.Therefore,results indicate that Er³⁺doped germanate-tellurite glass is a promising candidate for efficient3?m laser.Finally,it was the conclusion of this dissertation,which generalized the innovative results of this dissertation and pointed out the drawbacks that needed to be improved.