Photoluminescence Properties Of Trivalent Rare-earth Ions In Multicompenent Germaniurm Tellurite Glasses

In the past decades,glasses doped with one or more of the RE ions are great potential materials for a variety of linear and nonlinear optical applications,including color displays,commumications,laser surgeries,phosphors,medical diagostics,etc.Among various rare-earth ions,trivalent holmium Ho³⁺ and erbium Er³⁺ have unique energy level structure,and unique characteristic emission in the visible region and near infrared region,especially a relatively long fluorescence lifetime and a relative large stimulated emission cross-section of ⁵I₇ level in Ho³⁺ ions.At present,substantial developments,as represented by Erbium(Er³⁺)-doped fiber amplifiers?EDFAs?,have brought a tremendous breakthrough in the fields of optical fiber communications,greatly improving the transmission capacity of information.However,as a result of the rapid increase in information traffic,it is necessary to further explore the new band optical amplifiers in the optical fiber communication fields.As the improved manufacturing process of silica glass fibers eliminates the hydroxyl?OH-?impurity and reduce the attention of OH-absorption to a promising degree of ⁰.3dB/km,the wavelength region near the zero-dispersion of silica fibers within 1.2¹.4?m may become potential signal bands to further enlarge the transmission capacity of the current optical network.Meanwhile,Ho³⁺ ions with infrared fluorescent emission in the range of 1.2¹.4?m.Therefore,it is significant and promising to explore new optical amplifiers operating at 1.2¹.4?m to bring a potential breakthrough in information traffic.Ever since Johson had reported the first laser behaviour at 2.0?m from Ho³⁺-doped CaWO₄ crystal in 1962,considerable researthes have been made on investigation of spectroscopic and lasing properties of Ho³⁺-doped various crystals and glasses.The ².0?m characteristics emission of Ho³⁺ is promising candidates for various application in laser medicine,remote sensing,monitoring of atmospheric and so on.The tellurite glasses are chose to the basic glass host.Among the oxide glasses,the maximum phonon energy of the tellurite glasses is lower than those in silicate glass,phosphate glass,borate glass,etc.Hence,RE ions can acquire efficient luminescence in tellurite glasses due to the lower phonon energy.The tellurite glasses exhibit good mechanical strength and high thermal stability for the non-oxide glasses,the glasses are expected to possess easier process for glass melting and optical fiber drawing.The followings are results this work achieved:1.In this work,Ho³⁺-doped and Ho³⁺/Yb³⁺-doped multicomponent germanium tellurite?MGT?glasses have been designed and fabricated using high temperature fusion method.According to the empirical formula,the maximum phonon energy of the MGT glasses is deduced to be 780 cm^-1,which results in efficient IR emissions.The radiative transitions can be analyzed by the Judd-Ofelt?J-O?theory based on the absorption of Ho³⁺,J-O parameters are derived to be ?₂=5.32×10^-20cm²,?₄=2.73×10^-20cm² and ?₆=1.12×10^-20cm²,respectively.Using these intensity parameters,some important radiation properties including spontaneous transition probabilities,branching ratios,and radiative lifetimes for the optical transitions of Ho³⁺ in MGT glasses are calculated.The maximum emission cross-sections of the ¹.2?m emission and ¹.4?m emission of Ho³⁺ in MGT glasses are 3.10×10^–21 and 1.81×10^–21cm²,and the theoretical gain corss-section is also obtained,indicating that Ho³⁺-doped MGT glass holds great promising for optical amplifier in the infrared region.The upconversion fluorescence spectrum of Ho³⁺/Yb³⁺-doped MGT glasses was investigated under 980 nm laser excitation,indicating that Yb³⁺ ions can effect energy to Ho³⁺ ions to realize sensitization.The maximum values of emission and absorption section for the ².0?m emission are solved to be 4.93×10^–21 and 5.42×10^–21cm².The emissions of Ho³⁺-doped and Ho³⁺/Yb³⁺-codoped MGT glasses holds great promise for developing optical amplifier and NIR laser materials.2.In this work,Er³⁺-doped and Er³⁺/Yb³⁺-doped MGT glasses have been designed and fabricated using high temperature fusion method.The radiative transitions belonging to the 4f2 configuration can be analyzed by the Judd-Ofelt theory based on the absorption of Er³⁺.Judd-Ofelt intensity parameters are derived to be ?₂=5.51×10^–20cm²,?₄=1.54×10^–20cm² and ?₆=1.02×10^–20cm² by a least-squares fitting approach,respectively,and the J-O intensity parameters are important to investigate the local structure and bonding in the vicinity of rare earth ions.Using these intensity parameters,some important radiation properties including spontaneous transition probabilities,branching ratios,and radiative lifetime for the optical transitions of Er³⁺ in MGT glasses are calculated.The upconversion fluorescence spectrum and the IR emission spectrum of Er³⁺/Yb³⁺-doped MGT glasses was investigated under 980 nm laser excitation.The maximum values of emission and absorption sections for the ¹.5?m emission are solved to be 7.46×10^–21 and 7.94×10^–21cm²,respectively.The large emission and absorption sections indicating that Er³⁺/Yb³⁺-doped MGT glasses are beneficial in achieving efficient NIR fluorescence,offer favorable prospects for developing NIR lasers.