Fabrication and Spectroscopic Properties of Heavily Pr³⁺ Doped Selenide Chalcogenide Glass and Fiber for Mid-infrared Fiber Laser Enhanced Publication

Fabrication and Spectroscopic Properties of Heavily Pr 3+ Doped Selenide Chalcogenide Glass and Fiber for Mid-infrared Fiber Laser 用于中红外光纤激光器的高Pr 3+ 掺杂硒化物硫系玻璃和光纤制备及其光谱特性 1 2 first-author 许晨煜（1998-），男，陕西咸阳人，硕士研究生，2019年于四川大学获得学士学位，主要从事稀土掺杂硫系玻璃光纤材料的研究。 http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35879972&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35879979&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35879976&type= 25.00000191 30.00000000 许晨煜 （1998-），男，陕西咸阳人，硕士研究生，2019年于四川大学获得学士学位，主要从事稀土掺杂硫系玻璃光纤材料的研究。 1 2 1 1 1 1 2 corresp E-mail： guoht_001@opt.ac.cn E-mail： guoht_001@opt.ac.cn guoht_001@opt.ac.cn 中国科学院西安光学精密机械研究所 瞬态光学与光子技术国家重点实验室， 陕西 西安　710119 中国科学院西安光学精密机械研究所 瞬态光学与光子技术国家重点实验室， 陕西 西安　710119 State Key Laboratory of Transient Optics and Photonics， Xi’an Institute of Optics and Precision Mechanics， Chinese Academy of Sciences， Xi’an 710119， China State Key Laboratory of Transient Optics and Photonics， Xi’an Institute of Optics and Precision Mechanics， Chinese Academy of Sciences， Xi’an 710119， China 中国科学院大学， 北京　100049 中国科学院大学， 北京　100049 University of Chinese Academy of Sciences， Beijing 100049， China University of Chinese Academy of Sciences， Beijing 100049， China In order to develop a high gain medium for fiber lasers operating at 3-5 μm waveband， 0-0.4%（in weight） Pr 3+ ions doped Ge 12 As 20.8 Ga 4 Se 63.2 selenide chalcogenide glasses were prepared and the 0.2%（in weight） Pr 3+ ions doped one was successfully drawn into step-index double-cladding fiber with the lowest loss of 2.95 dB/m@6.58 μm by a multistage rod-in-tube method. The electron-probe measure microanalysis（EPMA）， X-ray diffraction（XRD）， differential scanning calorimeter（DSC）， field emission transmission electron microscope（FE-TEM）， transmission and mid-infrared fluorescence spectra were carried out to analyze the dispersion of Pr 3+ ions in glass， the impurity contents，thermal and optical changes caused by the Pr 3+ ions’ introduction. By analyzing the absorption and emission measurements of the serial glasses with the Judd-Ofelt theory， the Judd-Ofelt strength parameters， transition probabilities， exited state lifetime， branching ratios， and emission cross-sections were also calculated. This selenide chalcogenide glass has high Pr 3+ ions’ solubility and emission characteristic， good thermal stability and fiber forming performance， indicating that it has potential to be used as mid-infrared laser working medium. 为了研发用于3~5 μm波段光纤激光器的增益介质，制备了重量百分比为0～0.4%不同浓度Pr 3+ 离子掺杂的Ge 12 As 20.8 Ga 4 Se 63.2 硒化物硫系玻璃。通过多级棒管法，重量百分比为0.2%的Pr 3+ 离子掺杂玻璃被成功拉制成阶跃型双包层光纤，损耗最低为2.95 dB/m（位于6.58 μm处）。采用电子探针显微分析（EPMA）、X射线衍射（XRD）、差示扫描量热（DSC）、场发射透射电子显微镜（FE⁃TEM）、透射光谱和中红外荧光光谱分析了玻璃中Pr 3+ 离子的分散性、杂质含量以及Pr 3+ 离子引入引起的热、光学性质变化。通过玻璃的吸收和发射光谱并结合Judd-Ofelt理论，计算了Judd-Ofelt强度参数、辐射跃迁几率、荧光寿命、荧光分支比和受激发射截面。这种硒化硫系玻璃具有较高的Pr 3+ 离子溶解度和中红外发光特性、良好的热稳定性和成纤性能，表明其具有作为中红外激光工作介质的潜力。 硫系玻璃 稀土离子 光谱学 中红外荧光 红外光纤 chalcogenide glass rare-earth ions spectroscopy mid-infrared fluorescence infrared fiber 1　Introduction 1 Rare-earth（RE） ions doped fiber lasers operating at mid-infrared（MIR） regions are of great interests due to their potential applications in fields of chemical sensing, air pollution monitoring, medical surgery, national defense, and etc [ 1 1 - 4 4 1-4 ] . Chalcogenide glasses（ChGs）, as hosts for RE ions, have their unique advantages. The ChGs’ phonon energies are as low as 250-425 cm -1 , especially in which the selenide glasses have lower phonon energies of 250-300 cm -1[ 5 5 ] . This results in lower probabilities of multi-phonon transitions for RE ions, making it easier to achieve higher efficient MIR transitions of RE ions. It is known that the RE ions doped fluoride fibers have achieved high-power laser output in 3 μm waveband [ 6 6 - 7 7 6-7 ] , and compared with fluoride ones, ChG fibers have no obvious advantage for laser output at below 4 μm. Because of this, in the past two decades, people paid much attention to realize laser output at ≥4 μm wavelength in ChG fibers [ 8 8 - 11 11 8-11 ] . However, there has been little experimental progress in the research of ChGs’ fibers in laser output. There are three main reasons including the low RE ions’ solubility, the still high multi-phonon relaxation rate of RE ions and the severe fiber loss originating from impurities’ absorption [ 12 12 - 13 13 12-13 ] . Recently, a longest laser output wavelength as well as 5.14 μm was reported in a 0.05%（in weight, the same below） Ce 3+ -doped Ge 15 As 21 Ga 1 Se 63 fiber with a 9 μm-core-diameter pumped by a 4.15 μm quantum cascade laser at room temperature [ 14 14 ] . Ge-As-Ga-Se（GAGSE） glass system is interested because of its two advantages. Firstly, compared with the stubborn S—H bonds in sulfide glasses, Se—H bonds are easier to be eliminated because of lower polarity and bond energy（339 kJ/mol for S—H and 314 kJ/mol for Se—H）. Secondly, the conventional As—Se system glasses have strong covalence, resulting in the tendency of clustering of RE ions and quenching of fluorescence. Based on the original glass network, the introduction of Ge can improve the compactness of glass grid and increase the laser damage threshold [ 15 15 - 16 16 15-16 ] , which means the glass can be pumped by a higher power laser. However, there are a large number of Se—Se bridging bonds and Ge—Se covalent bonds in Ge—As—Se, which cannot compensate the high coordination number of RE ions, resulting in the low RE's solubility. Ga is further introduced to compensate for negative local environment of positive RE ions by forming Ga—Se—RE 3+ [ 9 9 ] . Introduction of Ga is effective to weaken the aggregation of RE ions in glass matrix. Several researchers have conducted many studies of RE ions doped GAGSE glasses and fibers. In 2014, Tang et al . prepared a 0.05% Pr 3+ ions doped GAGSE fiber by the extrusion method, and the lowest loss of fiber is 2.8 dB/m at 6.65 μm [ 8 8 ] . In 2018, Liu et al . prepared the Pr 3+ ions doped Ge 10 As 24 Ga 4 Se 62 glass and fiber with an optimal doping concentration of 0.2%. The 250/125 μm（cladding diameter/core diameter）, 0.2% doped step-index fiber exhibited the lowest loss of 3.5 dB/m at 6.9 μm. The fiber loss is about 10 dB/m at 2.9 μm caused by O—H bonds and 7 dB/m at 6.3 μm caused by H 2 O molecule [ 9 9 ] . In order to remove impurities and achieve low-loss GAGSE fibers, Shiryaev et al . reported a special chemical reaction device to transfer the GaI 3 vapor stream into the reactor for preparation of Ge 16 As 17 Ga 3 -Se 64 glasses [ 17 17 ] . This provides a practical idea for the preparation and purification of Ga-containing GAGSE glasses. In 2018, they successfully fabricated a low-loss Ge 25 As 15 Ga 3 Se 57 single-index fiber by using metallic aluminum and TeCl 4 for purification. The minimum fiber loss is 0.6 dB/m at 6.7 μm and the optical loss is about 5 dB/m at 4.58 μm caused by Se—H bonds [ 18 18 ] . However, there are still few reports about fiber laser output of Pr 3+ ions. This is mainly because the severe absorption of impurities and weak fluorescence intensity in Pr 3+ doped ChG fibers. So far, the doping concentration of Pr 3+ ions in ChG fibers reported is relatively low（usually 0.5%）. Therefore, the successful fabrication of a heavily Pr 3+ doped CHG fiber with low impurity absorption has become an urgent requirement. In this work, a modified glass composition of Ge 12 As 20.8 Ga 4 Se 63.2 was designed and a serial glasses doped with different concentration of Pr 3+ ions were prepared. This composition glass has higher Pr 3+ ions solubility（at least 0.4% without crystallization）, and the 0.2% Pr 3+ -doped glass was drawn into fiber with double-cladding structure. For reducing content of impurities（oxygen, hydrogen, carbon, silicon, and etc .）, the raw materials were distilled and the glasses were introduced with chemical impurity removal reagent. The absorption and emission spectra of bulk glasses were investigated and Judd-Ofelt intensity parameters were calculated. Broadband MIR luminescence of Pr 3+ ions in the region of 3.3-5.5 μm was observed, and the stimulated emission cross-section, radiation lifetime and other parameters were calculated. 2　Experiment 1 2.1　Glass Preparation and Fiber Drawing 2 Ge 12 As 20.8 Ga 4 Se 63.2 glass samples doped with 0, 0.05%, 0.1%, 0.2%, 0.3% and 0.4% in weight of Pr 3+ ions（denoted as GAGSE-undoped, GAGSE-0.05, GAGSE-0.1, GAGSE-0.2, GAGSE-0.3 and GAGSE-0.4） were prepared by melt quenching method. The raw materials of Ge（6N, grains, Nanjing Germanium Co., Ltd., RRC）, Ga（7N, grains, Aladdin Industrial Co. Ltd., RRC） and Praseodymium powder（3N, powder, Aladdin Industrial Co. Ltd., RRC） were respectively packed in ampoules and heated to remove volatile impurities. The As（7N, grains, Mount Emei Jiamei High Pure Material Co. Ltd., R.R.C.） and Se （6N, Aladdin Industrial Co. Ltd., RRC） were purified by a multi-stage distillation progress. All of the raw materials were weighed by an analytical balance （Sartorius, resolution of 0.001 g） in the glovebox （N 2 -filled, O 2 ≤10 -8 , H 2 O≤10 -8 ）, then loaded Ge, As, Se into a pre-treated quartz ampoule （800 ℃ for 12 h, under vacuum of 10 -3 Pa）. The ampoule was sealed under vacuum（10 -3 Pa）, and initially melted at 900 ℃ for 10 h to homogenize host glasses. The initial melted sample was transferred to a customized distillation ampoule, and Al foil（5N, Aladdin Industrial Co. Ltd., RRC） was introduced as deoxidizer. The distilled compound was then mixed with Ga and Pr powder and melted at 850 ℃ for 8 h. Subsequently, the quartz ampoule containing the molten glass was quenched, annealed near the glass transition temperature, and slowly cooled to the room temperature. The samples were cut into disks with a diameter of 12 mm and thickness of 3 mm, and mirror polished of both sides for following measurements. The glass sample which has the best optical and thermal properties was selected to be drawn into fiber by a multistage rod-in-tube method（see Fig. 1 Fig. 1 ）. In order to achieve single-mode transmission and control the diameter of fiber easily during the fiber drawing, a double-cladding structure was designed. The cladding tubes were prepared by the rotational casting method. After the core rod and inner-cladding tube were combined, they were pre-drawn into a slim rod（external diameter d =2.6 mm）. Then we assembled this preform with a thick outer-cladding tube which has a small hole through the center（internal diameter d′ =3.0 mm）, then coated it with FEP tube（external diameter d =15.0 mm）. Finally, the single-mode, double-cladding fiber with a diameter of 125 μm was drawn from the assembly. The optical fiber draw tower （SG Control, UK; MT-600N） is equipped with a built-in furnace which heated the preform to 440 ℃ at a heating rate of 2 ℃/min and kept this temperature to draw the optical fiber. During the drawing process, the He was introduced for atmosphere protection. 2.2　Physical and Optical Measurements 2 To figure out the composition deviation of the glass samples caused by the chemical purification treatment, the electron-probe measure microanalysis （EPMA, JEOLJXA-8230） was carried out. All samples were analyzed for the presence of crystalline phases by X-ray diffraction（XRD） （Bruker D8 ADVANCE with Cu radiation, a power of 40 kV, 40 mA, a step size of 0.02°（2 θ ） and step time of 0.1 s）. The thermal characteristics of the samples were analyzed by a Differential Scanning Calorimeter（NETZSCH DSC 404 F3）. 15 mg of glass powder was put into an aluminum crucible and heated to 400 ℃ under the protection of flowing atmosphere（N 2 ） with a heating rate of 10 ℃/min. The Field Emission Transmission Electron Microscope（FE-TEM）（FEI-Talos F200S/FEI Tecnai G2 F20 X-Twin） was used to verify the amorphous properties of the glass and the dispersion of RE ions with an Energy Dispersive Spectrometer （EDS）. The accelerating voltage regulation range is 20-200 kV and the maximum magnification can exceed 1 000 000 times. The point resolution and line resolution can reach 0.24 nm and 0.102 nm, respectively. The glass samples for FE-TEM are ground into fine powder, and then dispersed in absolute ethanol. The density measurement of the samples is Archimedes method, using a high-precision balance with special accessories. UV-VIS-NIR transmission spectrum of glass was measured by a spectrophotometer（JASCO V-570）. The region was 400-2 500 nm and the step length was 2 nm. FT-IR spectroscopy was measured by BRUKER VERTEX 70 and the region was 2-23 μm. The MIR fluorescence spectrum was measured by a fluorescence spectrometer（FSP920; Edinburgh Instruments Ltd., UK） equipped with a liquid-nitrogen cooled InSb detector（C4159-5671; HAMAMATSU, JPN）. The measurement wavelength was 2 300-5 500 nm and the spectral step size was 2 nm, pumped by a 2 μm CW laser. 3　Results and Discussion 1 3.1　Amorphous and Thermal Properties 2 Tab.1 Tab.1 is the EPMA analytical compositions of the undoped GAGSE glass sample after chemical purification treatment. Compared with original chemical composition, the deviation is so small that it can be accepted; thus, we regarded that the purified sample remains the original composition. *The results of these three elements are inauthentic due to the value of error. Composition Theoretical chemical composition/% Measured composition/% Error/% Ge 12 11.23 1.32 As 20.8 20.23 0.83 Ga 4 3.60 2.68 Se 63.2 64.19 0.59 O 0 0.59 * 22.3 Si 0 0.16 * 26.5 Al 0 0 * 100 Fig.2 Fig.2 shows the XRD patterns of all Pr 3+ ions doped glass samples. Even the sample doped with high concentration Pr 3+ ions as well as 0.4% has no obvious crystallization peaks. In order to make sure of amorphous properties and verify the dispersion of RE ions, the TEM test was further carried out, and the results are shown in Fig. 3 3 and 4 4 . In both HR-TEM images of GAGSE-0.2 and GAGSE-0.3 samples, no crystal fringe is observed, indicating that the heavily Pr 3+ ions doped samples still maintain the amorphous state. From the EDS results, it is obvious that all elements are dispersed evenly in the matrix. Comparing the EDS results of GAGSE-0.2 and GAGSE-0.3, it can be seen that the Pr 3+ gathers a little more densely in some local area when the Pr 3+ ions' concentration increases. Tab.2 Tab.2 shows the characteristic temperatures of all Pr 3+ doped glasses. For the GAGSE-undoped glass, the transition temperature（ T g ） is 212 ℃ and the initial crystallization temperature（ T x ） is 336 ℃. Parameter of Δ T is used to evaluate the crystallization resistance and vitrification ability of glass. The larger value of Δ T indicates higher glass forming ability and better thermal stability. The Δ T of GAGSE-undoped glass is about 124 ℃, indicating that the Ge 12 As 20.8 Ga 4 Se 63.2 glass has great thermal stability as a RE matrix glass. This is beneficial for fiber drawing in the next experiment. When the Pr 3+ ions are introduced into the matix glass, the T g is slightly increased whereas T x is decreased. It is obvious that the GAGSE-0.4 glass still has a lage Δ T vlaue as well as 105 ℃. Even the content of Pr 3+ reaches 0.4%, the thermal stability of the glass is still suitable for fiber drawing. Sample T g /℃ T x /℃ Δ T /℃ GAGSE‑undoped 212 336 124 GAGSE‑0.1 215 334 119 GAGSE‑0.2 217 331 114 GAGSE‑0.3 220 330 110 GAGSE‑0.4 223 328 105 3.2　Absorption and Emission Properties 2 Fig.5 Fig.5 shows the absorption spectra of 0.05%-0.4% Pr 3+ ions doped glasses in the wavelength range of 800-2 500 nm and the electronic energy levels of Pr 3+ ion. The four obvious absorption bands centered at 1 064, 1 494, 1 608，2036 nm correspond to the transitions from ground energy level of 3 H 4 to the excited levels of 1 G 4 , 3 F 4 , 3 F 3 and 3 F 2 , respectively. The cut-off edge is about 850 nm at the short wavelength because of the band gap absorption. The absorption coefficient of Pr 3+ ions in Ge 12 As 20.8 Ga 4 Se 63.2 glass increases approximately linearly from 0.05% to 0.4%（see Fig.6 Fig.6 ）, which confirms the Pr 3+ ions were dissolved almost homogeneously in the glass. Based on the absorption spectrum and basic physical parameters, the Judd-Ofelt analysis is used to evaluate the luminescence characteristics [ 19 19 - 20 20 19-20 ] . The oscillator strengths, Judd-Ofelt intensity parameters Ω t （ t =2, 4, 6） were calculated and summarized in Tab.3 Tab.3 . The values of other reported system glasses are also summarized for comparison. The Ω t （ t =2, 4, 6） are related to the local environment nearby the RE ions. Ω 2 is mainly affected by polarized and asymmetric environment around RE ions, Ω 4 is mainly affected by the acidity and alkaline, and Ω 6 is related to the rigidity of glass [ 21 21 - 23 23 21-23 ] . In addition, the value of Ω 4 / Ω 6 is used to evaluate the spontaneous emission characteristics of RE ions. The two ground state electronic absorption peaks of 3 H 4 → 3 F 4 , 3 F 3 overlap each other. For J-O analysis, this wide absorption peak can be divided into two characteristic peaks. Taking sample GAGSE-0.4 as an example, the result of division is shown in Fig.7 Fig.7 . The fitting mode is Gaussian-Lorentz and the R 2 is 0.997 455. It can be found that the Ω t suddenly changed when the concentration of Pr 3+ ions increased to 0.3%. The sudden increase of Ω 2 implies the asymmetric environment was changed around RE ions. In general, the low symmetry of polyhedral structure and high covalency of constituent bonds will lead to a lager oscillator strength. Compared with the other hosts, Pr 3+ ions doped GAGSE glass has the lager oscillator strength. 3 Glass 4 J‑O parameters/（10 -20 cm 2 ） 4 Oscillator strength/10 -6 3 Reference 2 Ω 2 2 Ω 4 2 Ω 6 2 Ω 4 / Ω 6 4 3 H 4 → 1 G 4 3 F 4 3 F 3 3 F 2 GAGSE‑0.05 2.37 16.51 8.59 1.92 1.096 13.194 28.857 17.356 5 This work GAGSE‑0.1 2.59 14.63 6.05 2.42 1.009 9.712 22.948 15.159 GAGSE‑0.2 2.5 14.15 5.86 2.41 1.074 9.412 22.22 14.663 GAGSE‑0.3 2.98 11.37 4.77 2.38 0.812 7.811 18.411 12.965 GAGSE‑0.4 3.3 10.17 4.73 2.15 0.764 7.497 17.136 12.8 Phosphate 4.26 4.33 6.27 0.69 0.250 10.540 10.640 5.000 ［ 24 24 ］ Fluorotellurite 3.57 6.60 5.18 1.27 0.409 4.543 9.668 6.357 ［ 25 25 ］ ZBLAN 0.94 6.54 3.84 1.70 3.14 4.05 2.09 0.99 ［ 26 26 ］ BKZ 4.92 14.08 8.48 1.66 — 5.49 12.08 7.89 ［ 27 27 ］ GAGS 10.4 4.78 10.4 0.46 — — — — ［ 28 28 ］ Fig.8 Fig.8 shows the infrared transmission spectra of blank and 0.05%-0.4% Pr 3+ ions doped GAGSE glasses. The infrared cut-off wavelengths are about 18 μm. Because the raw materials have been purified, there are no obvious peaks of impurity absorptions before 9 μm. The strongest absorption peak is at around 4.6 μm which is caused by the absorption of 3 H 5 energy level of Pr 3+ ions. However, the absorption of Se—H vibration（3.5 μm and 4.12 μm） with the introduction of RE ions cannot be completely excluded. Besides, the weak absorption peak at 6.3 μm is caused by the impurity absorption of H 2 O. In addition, comparing the Pr 3+ ions doped and undoped glasses’ spectra, it can be found that the Se—H vibration at 3.5 μm and 4.12 μm will appear due to the introduction of Pr 3+ ions. This is probably because the raw material of Praseodymium powder was generally prepared by a hydrogenation method, which will result in a lot of H elements absorbed in the powder can hard to be totally removed through the subsequent processing process. Moreover, the strong absorption peaks at 9.7 μm and 11.8 μm should be caused by the vibration of As—O and Ge—O, respectively [ 17 17 ] . In fact, it can be seen from the experimental results that the present purified process has an effect on the removal of Se—H, —OH and H 2 O, but has no obvious work for the elimination of As—O and Ge—O. Fig.9 Fig.9 shows the MIR emission spectra of 0.05%-0.4% Pr 3+ ions doped Ge 12 As 20.8 Ga 4 Se 63.2 glasses ranging from 2 300 nm to 5 500 nm pumped by a 2.0 μm laser. The Pr 3+ ions have a very wide emission band from 3.4 nm to 5.5 μm. The emission peaks, which centered at 2.33, 3.1, 3.3 μm, correspond to the transitions of 3 F 2 / 3 H 6 → 3 H 4 , 1 G 4 → 3 F 3 , and 1 G 4 → 3 F 4 , respectively. The electrons that have already been excited to the 3 F 2 energy level will continue to be excited to the higher 1 G 4 energy level when pumped by a 2.0 μm laser, as shown in Fig. 10 Fig. 10 . Actually, the emission peak at 2.33 μm is also contributed by the transition of 3 F 4 / 3 F 3 → 3 H 5 [ 29 29 ] . The broadband luminescence is contributed by the superposition of emission peaks（ i.e ., 3 F 4 → 3 F 2 / 3 H 6 , 3 F 3 → 3 H 6 , 3 F 2 → 3 H 5 , 3 H 6 → 3 H 5 and 3 H 5 → 3 H 4 ）. In addition, the dip at 4.24 μm is ascribed to the absorption of CO 2 in the air of the spectrometer and the dip at 4.55 μm is caused by the Se—H bond impurity of the sample itself [ 8 8 - 9 9 8-9 , 30 30 ] . From the fluorescence spectral variation, it can be seen that when the Pr 3+ ions' concentration is lower than 0.2%， the fluorescence intensity increases with the increasing of the Pr 3+ ions' concentration and reaches the maximum at 0.2%. It can also be found that further increasing of Pr 3+ ions' concentration will enhance the intensities of emissions at 2.33 μm and 3.1 μm but the intensity of wide emission band（3.4-5.5 μm） is decreased. This phenomenon indicates that when the concentration of Pr 3+ ions is less than or equal 0.2%, most of the Pr 3+ ions can be evenly distributed in the glass matrix by mainly forming Pr—Se—Ga bonds. However, when the concentration of Pr 3+ ions is further increased, the finite non-bridging Se can no longer provide enough negative coordination for the Pr 3+ ions. Therefore, the Pr 3+ ions gradually begin to be clustered（see Fig.3 Fig.3 （d）） to share ligands by forming of Pr—Se—Pr instead of Pr—Se—Ga ones. In this way, the part of Pr 3+ ions' clusters contribute little to MIR fluorescence, which ultimately leads to fluorescence quenching [ 9 9 , 30 30 ] . Therefore, according to the J-O parameters and fluorescence spectra, it is concluded that the optimal doping concentration of Pr 3+ ions in this glass matrix is 0.2%. When the concentration is higher than 0.2%, the clusters will bring about fluorescence quenching by depopulating the excited states. The stimulated emission cross-section of Pr 3+ in this glass matrix is calculated basing on the Füchtbauer-Ladenburg equation [ 31 31 ] ： <math display="block" id="M1"><msub><mrow><mi>σ</mi></mrow><mrow><mi mathvariant="normal">e</mi><mi mathvariant="normal">m</mi><mi mathvariant="normal">i</mi></mrow></msub><mfenced separators="|"><mrow><mi>λ</mi></mrow></mfenced><mo>=</mo><mfrac><mrow><msubsup><mrow><mi>λ</mi></mrow><mrow><mi mathvariant="normal">p</mi></mrow><mrow><mn mathvariant="normal">4</mn></mrow></msubsup><mi>λ</mi><mi>I</mi><mfenced separators="|"><mrow><mi>λ</mi></mrow></mfenced></mrow><mrow><mn mathvariant="normal">8</mn><mi mathvariant="normal">π</mi><mi>c</mi><msup><mrow><mi>n</mi></mrow><mrow><mn mathvariant="normal">2</mn></mrow></msup><msub><mrow><mi>τ</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">d</mi></mrow></msub><mo>∫</mo><mi>λ</mi><mi>I</mi><mfenced separators="|"><mrow><mi>λ</mi></mrow></mfenced><mi mathvariant="normal">d</mi><mi>λ</mi></mrow></mfrac><mo>,</mo></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880057&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880055&type= 49.02199936 11.76866722 , in which the effective line-width, λ eff , of fluorescence band is defined by: <math display="block" id="M3"><mi mathvariant="normal">Δ</mi><msub><mrow><mi>λ</mi></mrow><mrow><mi mathvariant="normal">e</mi><mi mathvariant="normal">f</mi><mi mathvariant="normal">f</mi></mrow></msub><mo>=</mo><mfrac><mrow><mo>∫</mo><mi>I</mi><mo stretchy="false">(</mo><mi>λ</mi><mo stretchy="false">)</mo><mi mathvariant="normal">d</mi><mi>λ</mi></mrow><mrow><msub><mrow><mi>I</mi></mrow><mrow><mi mathvariant="normal">m</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">x</mi></mrow></msub></mrow></mfrac></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880061&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880058&type= 25.90800095 11.43000031 ， <math display="block" id="M4"><mtext>  </mtext></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880064&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880062&type= 6.26533365 3.47133350 the <math id="M5"><mo>∫</mo><mi>I</mi><mo stretchy="false">(</mo><mi>λ</mi><mo stretchy="false">)</mo><mi mathvariant="normal">d</mi><mi>λ</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880067&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880066&type= 13.80066681 6.43466663 is the effective peak area and <math id="M6"><msub><mrow><mi>I</mi></mrow><mrow><mi mathvariant="normal">m</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">x</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880069&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880068&type= 4.57200003 3.72533321 is the maximum intensity of each emission peak. <math id="M7"><msub><mrow><mi>λ</mi></mrow><mrow><mi mathvariant="normal">p</mi></mrow></msub><mtext> </mtext></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880071&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880070&type= 4.23333359 3.80999994 is the center wavelength of emission peak. <math id="M8"><mtext> </mtext><mi>c</mi></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880073&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880072&type= 2.28600001 2.70933342 is speed of light, n is refractive index, <math id="M9"><msub><mrow><mi>τ</mi></mrow><mrow><mi mathvariant="normal">r</mi><mi mathvariant="normal">a</mi><mi mathvariant="normal">d</mi></mrow></msub></math> http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880075&type= http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=35880074&type= 4.48733330 3.72533321 is the radiation lifetime of transition. The calculated results are listed in Tab.4 Tab.4 . The GAGSE-0.2 glass has a large σ emi , long upper state lifetime, and good branching ratios for transition 3 H 5 → 3 H 4 and 3 H 6 → 3 H 5 . This is mainly because the chalcogenide glass has a larger refractive index and higher degree of covalent bonding. These characteristics of GAGSE-0.2 glass make it possible for MIR fiber amplifiers and lasers. Glass Transition λ emi /nm λ eff /nm τ rad /ms β /% A rad /s -1 σ emi /（10 -20 cm 2 ） 6 GAGSE‑0.05 1 G 4 → 3 F 4 3 434 131.22 2 5.92 1.86 133.94 2.491 1 G 4 → 3 F 3 3 000 82.63 0.48 34.88 0.677 3 F 3 → 3 H 5 2 370 — 0.80 15.41 1 243.76 — 3 F 4 → 3 H 5 2 150 — 0.62 35.71 1 592.57 — 3 H 5 → 3 H 4 4 814 752.79 8.59 100 116.36 1.582 3 H 6 → 3 H 5 4 600 734.94 8.16 43.26 122.43 1.401 8 6 GAGSE‑0.1 1 G 4 → 3 F 4 3 434 137.14 2 8.18 1.68 96.49 1.717 1 G 4 → 3 F 3 3 000 78.80 0.44 25.70 0.523 3 F 3 → 3 H 5 2 370 — 0.89 17.06 1 116.32 — 3 F 4 → 3 H 5 2 150 — 0.77 37.87 1 290.25 — 3 H 5 → 3 H 4 4 814 743.23 10.90 100 91.66 1.305 3 H 6 → 3 H 5 4 600 730.65 10.32 44.16 96.82 1.114 7 6 GAGSE‑0.2 1 G 4 → 3 F 4 3 434 151.73 2 8.45 1.68 93.43 1.492 1 G 4 → 3 F 3 3 000 102.36 0.45 24.88 0.333 3 F 3 → 3 H 5 2 370 — 0.92 17.04 1 079.16 — 3 F 4 → 3 H 5 2 150 — 0.80 37.86 1 248.55 — 3 H 5 → 3 H 4 4 814 741.76 11.25 100 88.84 1.193 3 H 6 → 3 H 5 4 600 722.42 10.65 44.19 93.83 1.066 7 6 GAGSE‑0.3 1 G 4 → 3 F 4 3 434 171.31 2 10.04 1.73 79.19 1.120 1 G 4 → 3 F 3 3 000 100.24 0.44 20.43 0.279 3 F 3 → 3 H 5 2 370 — 1.03 18.45 968.83 — 3 F 4 → 3 H 5 2 150 — 0.98 37.50 1 013.12 — 3 H 5 → 3 H 4 4 814 728.76 13.51 100 77.94 1.011 3 H 6 → 3 H 5 4 600 752.17 12.82 44.81 93.83 0.850 7 6 GAGSE‑0.4 1 G 4 → 3 F 4 3 434 163.56 2 10.04 1.83 79.66 1.180 1 G 4 → 3 F 3 3 000 103.23 0.46 19.98 0.265 3 F 3 → 3 H 5 2 370 — 1.07 18.77 933.02 — 3 F 4 → 3 H 5 2 150 — 1.05 36.39 945.62 — 3 H 5 → 3 H 4 4 814 719.76 14.06 100 71.10 0.984 3 H 6 → 3 H 5 4 600 749.27 13.39 44.85 74.63 0.817 3.3　Fiber Fabrication and Loss 2 The GAGSE-0.2 glass sample was selected and drawn into a single-mode, double-cladding fiber. Fig.11 Fig.11 shows the sectional micrographs at different magnifications and the outermost layer is FEP plastic. The diameter of core, inner cladding and outer cladding are 15, 140, 170 μm, respectively. The refractive indexes（ n core =2.613, n inner-cladding =2.611, n outer-cladding =2.587） were measured by an IR VASE Mark Ⅱ Spectroscopic Ellipsometer at 2 μm wavelength. The numerical apertures（N.A.） between core and inner cladding is about 0.10, between inner and outer cladding is about 0.35, which were calculated at 2 μm wavelength. There is no obvious crystallization can be found on the surface of fiber, indicating this glass has good ability for fiber fabrication. The fiber loss of GAGSE-0.2 double-cladding fiber is shown in Fig.12 Fig.12 . The test method is truncation method. The fiber has a lowest loss of 2.95 dB/m at 6.58 μm. The absorption band at 4.6 μm is due to the Pr 3+ （ 3 H 5 → 3 H 4 ） and Se—H bonds. The absorption bands at 3.5, 6.3, 7.9 μm should be—OH, Se—H, H 2 O and oxide impurities（Ge—O, As—O）, respectively. 4　Conclusion 1 The new glass composition in the Ge-As-Ga-Se chalcogenide system, i.e . Ge 12 As 20.8 Ga 4 Se 63.2 shows high Pr 3+ ions' solubility（0.4% in weight at maximum） and good thermal characteristic（ T x － T g ≥105 ℃）. The Pr 3+ ions have a very wide emission band from 3.4 μm to 5.5 μm and the 0.2%（in weight） Pr 3+ ions doped glass shows the best mid-infrared emission characteristic. Through physical and chemical purification, the impurity content can be effectively reduced to an acceptable level. The 0.2%（in weight） Pr 3+ ions doped Ge 12 As 20.8 Ga 4 Se 63.2 　 glass was successfully drawn into a step-index, double-cladding fiber by a multistage rod-in-tube method, and the lowest loss is 2.95 dB/m at 6.58 μm. To sum up, it should be a good potential gain medium to realize mid-infrared fiber lasers working at 3.5-5.5 μm. 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XU Chen-yu,CUI Jian,XU Yan-tao,et al.Fabrication and Spectroscopic Properties of Heavily Pr3+ Doped Selenide Chalcogenide Glass and Fiber for Mid-infrared Fiber Laser[J].Chinese Journal of Luminescence,2022,43(06):851-861. 国家自然科学基金（62005312，62090065，61935006）； 中国科学院创新交叉团队项目（JCTD‑2018‑19）资助 Supported by National Natural Science Foundation of China（62005312，62090065，61935006）； Chinese Academy of Sciences Interdisciplinary Innovation Team Project（JCTD‑2018‑19） 2022-03-15 2022-03-27 2022-06-05 2022-10-19 发光学报 6 43