The Mechanism Of Efficient Ultra-broadband NIR Luminescence And Spectral Control In Low Concentration Bi-doped Glass

Bismuth doped glass materials have an ultra-broad near-infrared(NIR)emission band in the region from 1000 nm to 1800 nm,which can cover the whole low-loss area of optical silica fiber.The full width at half maximum(FWHM)exceed 300 nm,and the fluorescence lifetime can reach several microseconds.Therefore,Bi-doped glass has the potential to be the media gain material for the new generation fiber amplifier,which can overcome the defect of RE-doped fiber amplifier.However,there are still many problems in the development of Bi-doped optical devices,such as,unclear of the NIR emission mechanism in Bi-doped glass,low absorption efficiency,unflatness of amplification band,low doping concentration in Bi-doped fiber etc.Among them,unclear of the NIR emission mechanism is the biggest obstacle to development of Bi-doped optical devices,and it is also the restricting for solving other problems.Therefore,its need more study on the NIR emission mechanism in Bi-doped glasses.Based on the cognition of the NIR emission in Bi-doped glass comes from the Bi with low valence.And the precipitation of metallic bismuth clusters or colloidal particles during the fiber drawing could be assigned for that due to remarkable self-reduction of bismuth ions at high temperature especially when bismuth doping content beyond 10000 ppm.In this work,the effect of nitride reduction agent(Si₃N₄,Al N,BN)addition,the types of alkaline earth metal ions,heat treatment parameter,and the Bi doping concentration on the NIR emission properties are studied.Moreover,the emission band can extend to 2?m by co-doping the Tm³⁺into Bi-doped germanate glasses.The emission properties of Bi-doped germanate glass,and Bi-,Te-,and Sb-doped germanosilicate glass were compared,and the NIR emission mechanism of Bi-doped glass is discussed.The detail results are listed as follows:1.When excited at 460 nm,there was a broadband NIR emission from 870 nm to1850nm with an independent 1500 nm emission peak can be observed in low concentration Bi doped germanate glass.The appearance of the 1500 nm emission peak make the FWHM enlarge over 500 nm,which can completely cover the optical fiber communication window.The NIR emission in Bi-doped germanate glasses will be significantly enhanced by adding the nitride reducing agent,indicating the Bi with low valence will be responsible for the NIR emission in Bi-doped glass.The addition of reducing agent will benefit to the formation of 1500 nm emission center.And the results show that there are multiple Bi-active NIR emission centers(BACs)co-exist in Bi-doped germanate glasses,and the ultra-broadband emission band comes from the co-excitation of the multiple emission centers.2.The effects of the types of alkaline earth metal ions on the Bi-related NIR emission properties were studied.(1).By comparative analyzing of the different spectra properties,it is believed that the BACs of emission bands at 950 nm and 1500nm have the close relevance.Meanwhile,the emission peaks near 1162 nm and 1500nm are correspond to the different BACs in the same coordination environment.(2).The energy levels of BAC(1093 nm)and BAC(1500 nm)were proposed,which based on analyzing the transmittance spectra,emission spectra,excitation spectra and 3D plot spectra.(3).The properties of Ge-ODC related emission and Bi-related NIR emission are different,indicating that there is no direct relationship between the BACs and Ge-ODC.3.In Bi-doped germanate glasses,the broad flatness NIR emission can be realized by adjusting the ratio of NIR emission centers to non-NIR emission centers and the ratio of different types of BACs,which can be achieved by adjusting the heat treating parameters and Bi-doping concentration.The similarities and differences of spectral properties among Bi doped germanate glass,silicate glass,and Bi-,Te,Sb-doped germanosilicate glass were suided.(1).The similar NIR emission properties can be observed in Bi,Te and Sb doped germanosilicate glass.Therefore,the NIR emission centers may have similar structure in those glasses.With the increase of doping concentration in Te-,Sb-doped glasses,the emission intensity gradually increases,indicating that all the types of NIR emission centers are relevant to the doped ions themselves.However,it is impossible to exclude the possibility that the NIR emission centers come from the combination of doped ions and defects in the glass.(2)The heat-traeating,loosen structure of glass,the addition of Ge O₂ and reduction agent will be benefit to the formation of the 1500 nm emission center,indicating the 1500 nm emission center may origin from the clusters which composed by the low-valence ions.4.The ultra-broad NIR emission band and the enhanced 1800 nm emission in Bi-Tm co-doped germanate glass were studied.The ultra-broad NIR emission band covering 860 nm-2250 nm can be achieved by co-doping Tm³⁺ions into Bi single-doped germanate glass,and FWHM can be up to 810 nm.The ultra-broad NIR emission band is derived from the co-excitation of the BACs and Tm³⁺ions.The results show that multiple BACs are involved in energy transfer processes with Tm³⁺,and different BACs have different energy transfer efficiency.The maximum energy transfer efficiency can be up to 85.6%,and the quantum efficiency of 1800 nm emission was significantly enhanced.Moreover,the mainly energy transfer processes between BAC(1093nm),BAC(1500nm)and Tm³⁺ions are discussed.