F Charpentier et aL/ Materials Letters 101(2013)21-24 a GeGaSbS: Pr"(500ppm) 0.006 GaSbse: Pr"(500ppm 0.004 co0≌Eu 0001 0.000 60080010001200140016001800200022002400 ength [nm Fig. 3. Pr+ doped Ga-Ge-Sb-S(Se)glasses absorption coefficient spectra. assume that the site around Dysprosium changes with increasing concentration without affecting the bond lengths, at least less than GeGaSbS: Pr l% of the latter. Without formation of re doped crystallites which GeGasbSe: Pr SeH would inevitably lead to a fluorescence spectrum structuring, the co Dyt coordination change tends to reveal environment variation hich may traduce dipole-dipole distance shortening for high Dy concentrations For Dysprosium doped Gas GezoSb1oS(Se)65 fibers and glasses, 0,003 after optical pumping in the H1/ or an upper level, the mid-IR mission at 4.35 um with a FWHM of about 300 nm comes from 0002 the transition between H12 and H13/ levels of Dy+( Fig. 2) Several absorption bands could be used to pump Dy+ ion, but the absorption at 920 nm(oabs -1.10-20 cm)appears to be the best choice as versatile and efficient laser diodes exist at this wave- H一HH→H 0.000 length. Therefore focused on sulfide matrix, the phonon energy 4000 4500 300-350 cm"-)provides a dominant non-radiative relaxation of wavelength [nm the upper levels, so the Hsp level relaxes non-radiatively to the emitting level. The emission cross-section, determined by Fig 4. Fluorescence spectra of Pr+ doped Ga-Ge-Sb-S(Se)fibers. the Fuchtbauer-Ladenburg method, of H1/+H132 transition (avg=4.24 um)of Dy+ doped Gas Gezo Sb1oS65, is seven times higher(Gem(H1p-H13/2)=18. 1 x 10-2 cm2 at 4.3 um, trad(Hn/ relatively easily into the network(consisting essentially of [Ges 2)=2.3 ms, B=13 %)than that of l9p-l1/ transition (Se)apl tetrahedra and [Sbs(Se )3/2] trigonal pyramids), thanks to (aavg=4.53 um)in the sulfide glass doped with Er+[12] the presence of locally modified charge densities of [GaS(Se)a/2I For Pr+ doped Gas GezoSb1oS(Se )65, the absorption measure- tetrahedra. The rE should form stable complexes with Ga avoiding ments show three absorption bands at 1, 1.5, and 2 um corre- the cluster formation detrimental to the mid-IR emission insofar ponding to the electron transitions from the Ha ground state to as the re/ Ga ratio remains low: otherwise, structural changes low absorption cross-section of 3H4+'GA transition implies that Gas zo Sb1os6s by EXAFS analyses observed in case of Dy+ IGA, (F4. F3), and (H. F2)states, respectively( fig 3). The very seem to occur around the re as the pumping is performed at 2 um(H, F2), the closest states to emitting levels. The emission observed in mid-IR is very broad (3.5-5.5 um), composed of H6-+Hs and Hs -+Ha transitionsAcknowledgments (Figs. 3 and 4). The ratio between these two transitions depends transition. Chalcogenide glasses contain some impurities like This work was supported by ANR SEED 2012 CGSuLab SH (in Ga-Ge-Sb-S)and-Seh (in Ga-Ge-Sb-Se)that provi otion at 4.0 and 4.6 um, respectively(Fig. 4). Even if the References concentration of such entities remains lower than 100 ppm after purification process, they can easily cause non-radiative relaxation [11 Sanghera Is agarwal glass-fiber-based Mid-IR due to their quasi-resonant phonon energy for mid-IR transitions IEEE J Sel To [12, 26]. It is therefore necessary to further improve purity of 2 Schweizer T nid-infrared laser transitions in gallium glasses enabling a fluorescence signal as wide and flat as possible m sulphide glass. J Lumin [3 Park B). Seo HS, Ahn T, choi YG, Jeon DY, Chung W]. Mid-infrared (3.5-5.5 um) Conclusion bers. J Lumin2008:128:1617-22 [4 Prudenzano V. Nazabal V. Smektala F heoretical study of cascade laser in erbium-doped chalcogenide glass fibers. Gez0Sb1oS(Se)6 as studied focusing on the 4-5 um emission band. I [5 Quimby RS, Shaw LB, Sanghera JS, Aggarwal ID Modeling of cascade lasing in quaternary matrices, the re ions can be inserted nics Technol Lett 2008: 20: 123-5assume that the site around Dysprosium changes with increasing concentration without affecting the bond lengths, at least less than 1% of the latter. Without formation of RE doped crystallites which would inevitably lead to a fluorescence spectrum structuring, the Dy3þ coordination change tends to reveal environment variation which may traduce dipole–dipole distance shortening for high Dy concentrations. For Dysprosium doped Ga5Ge20Sb10S(Se)65 fibers and glasses, after optical pumping in the 6 H11/2 or an upper level, the mid-IR emission at 4.35 mm with a FWHM of about 300 nm comes from the transition between 6 H11/2 and 6 H13/2 levels of Dy3þ (Fig. 2). Several absorption bands could be used to pump Dy3þ ion, but the absorption at 920 nm (sabs∼1.10−20 cm2 ) appears to be the best choice as versatile and efficient laser diodes exist at this wave￾length. Therefore focused on sulfide matrix, the phonon energy (300–350 cm−1 ) provides a dominant non-radiative relaxation of the upper levels, so the 6 H5/2 level relaxes non-radiatively to the 6 H11/2 emitting level. The emission cross-section, determined by the Füchtbauer–Ladenburg method, of 6 H11/2-6 H13/2 transition (λavg¼4.24 mm) of Dy3þ doped Ga5Ge20Sb10S65, is seven times higher (sem( 6 H11/2-6 H13/2)¼18.1 10−21 cm2 at 4.3 mm, τrad( 6 H11/ 2)¼2.3 ms, β¼13 %) than that of 4 I9/2-4 I11/2 transition (λavg¼4.53 mm) in the sulfide glass doped with Er3þ [12]. For Pr3þ doped Ga5Ge20Sb10S(Se)65, the absorption measure￾ments show three absorption bands at 1, 1.5, and 2 mm corre￾sponding to the electron transitions from the 3 H4 ground state to 1 G4, (3 F4, 3 F3), and (3 H6, 3 F2) states, respectively (Fig. 3). The very low absorption cross-section of 3 H4-1 G4 transition implies that the pumping is performed at 2 mm (3 H6, 3 F2), the closest states to emitting levels. The emission observed in mid-IR is very broad (3.5–5.5 mm), composed of 3 H6-3 H5 and 3 H5-3 H4 transitions (Figs. 3 and 4). The ratio between these two transitions depends on the matrix and on the reabsorption due to the 3 H4-3 H5 transition. Chalcogenide glasses contain some impurities like – SH (in Ga–Ge–Sb–S) and –SeH (in Ga–Ge–Sb–Se) that provide absorption at 4.0 and 4.6 mm, respectively (Fig. 4). Even if the concentration of such entities remains lower than 100 ppm after purification process, they can easily cause non-radiative relaxation due to their quasi-resonant phonon energy for mid-IR transitions [12,26]. It is therefore necessary to further improve purity of glasses enabling a fluorescence signal as wide and flat as possible. 4. Conclusion The spectroscopy of Dy3þ or Pr3þdoped Ga5Ge20Sb10S(Se)65 glasses was studied focusing on the 4–5 mm emission band. In prepared quaternary matrices, the RE ions can be inserted relatively easily into the network (consisting essentially of [GeS (Se)4/2] tetrahedra and [SbS(Se)3/2] trigonal pyramids), thanks to the presence of locally modified charge densities of [GaS(Se)4/2] − tetrahedra. The RE should form stable complexes with Ga avoiding the cluster formation detrimental to the mid-IR emission insofar as the RE/Ga ratio remains low; otherwise, structural changes seem to occur around the RE as observed in case of Dy3þ: Ga5Ge20Sb10S65 by EXAFS analyses. Acknowledgments This work was supported by ANR SEED 2012 CGSμLab. References [1] Sanghera JS, Shaw LB, Aggarwal ID. Chalcogenide glass-fiber-based Mid-IR sources and applications. IEEE J Sel Top Quantum Electron 2009;15:114–9. [2] Schweizer T, Hewak DW, Samson BN, Payne DN. Spectroscopy of potential mid-infrared laser transitions in gallium lanthanum sulphide glass. J Lumin 1997;72-4:419–21. [3] Park BJ, Seo HS, Ahn JT, Choi YG, Jeon DY, Chung WJ. Mid-infrared (3.5-5.5 μm) spectroscopic properties of Pr3þ-doped Ge–Ga–Sb–Se glasses and optical fibers. J Lumin 2008;128:1617–22. [4] Prudenzano F, Mescia L, Allegretti L, Moizan V, Nazabal V, Smektala F. Theoretical study of cascade laser in erbium-doped chalcogenide glass fibers. Opt Mater 2010;33:241–5. [5] Quimby RS, Shaw LB, Sanghera JS, Aggarwal ID. Modeling of cascade lasing in Dy:chalcogenide glass fiber laser with efficient output at 4.5 μm. IEEE Photo￾nics Technol Lett 2008;20:123–5. Fig. 3. Pr3þ doped Ga–Ge–Sb–S(Se) glasses absorption coefficient spectra. Fig. 4. Fluorescence spectra of Pr3þ doped Ga–Ge–Sb–S(Se) fibers. F. Charpentier et al. / Materials Letters 101 (2013) 21–24 23