Optical spectroscopy and upconversion luminescence in Nd3+ doped Ga10Ge25S65 glass Vineet Kumar Rai, Cid B. de Araújo, Y. Ledemi, B. Bureau, M. Poulain et al. Citation: J. Appl. Phys. 106, 103512 (2009); doi: 10.1063/1.3259439 View online: http://dx.doi.org/10.1063/1.3259439 View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v106/i10 Published by the AIP Publishing LLC. Additional information on J. Appl. Phys. Journal Homepage: http://jap.aip.org/ Journal Information: http://jap.aip.org/about/about_the_journal Top downloads: http://jap.aip.org/features/most_downloaded Information for Authors: http://jap.aip.org/authors Downloaded 11 Jul 2013 to 186.217.234.138. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jap.aip.org/about/rights_and_permissions http://jap.aip.org/?ver=pdfcov http://oasc12039.247realmedia.com/RealMedia/ads/click_lx.ads/www.aip.org/pt/adcenter/pdfcover_test/L-37/932441298/x01/AIP-PT/JAP_CoverPg_0513/AAIDBI_ad.jpg/6c527a6a7131454a5049734141754f37?x http://jap.aip.org/search?sortby=newestdate&q=&searchzone=2&searchtype=searchin&faceted=faceted&key=AIP_ALL&possible1=Vineet Kumar Rai&possible1zone=author&alias=&displayid=AIP&ver=pdfcov http://jap.aip.org/search?sortby=newestdate&q=&searchzone=2&searchtype=searchin&faceted=faceted&key=AIP_ALL&possible1=Cid B. de Ara�jo&possible1zone=author&alias=&displayid=AIP&ver=pdfcov http://jap.aip.org/search?sortby=newestdate&q=&searchzone=2&searchtype=searchin&faceted=faceted&key=AIP_ALL&possible1=Y. Ledemi&possible1zone=author&alias=&displayid=AIP&ver=pdfcov http://jap.aip.org/search?sortby=newestdate&q=&searchzone=2&searchtype=searchin&faceted=faceted&key=AIP_ALL&possible1=B. Bureau&possible1zone=author&alias=&displayid=AIP&ver=pdfcov http://jap.aip.org/search?sortby=newestdate&q=&searchzone=2&searchtype=searchin&faceted=faceted&key=AIP_ALL&possible1=M. Poulain&possible1zone=author&alias=&displayid=AIP&ver=pdfcov http://jap.aip.org/?ver=pdfcov http://link.aip.org/link/doi/10.1063/1.3259439?ver=pdfcov http://jap.aip.org/resource/1/JAPIAU/v106/i10?ver=pdfcov http://www.aip.org/?ver=pdfcov http://jap.aip.org/?ver=pdfcov http://jap.aip.org/about/about_the_journal?ver=pdfcov http://jap.aip.org/features/most_downloaded?ver=pdfcov http://jap.aip.org/authors?ver=pdfcov Optical spectroscopy and upconversion luminescence in Nd3+ doped Ga10Ge25S65 glass Vineet Kumar Rai,1 Cid B. de Araújo,2,a� Y. Ledemi,3,4 B. Bureau,3 M. Poulain,3 and Y. Messaddeq4 1Department of Applied Physics, Indian School of Mines University, 826004 Dhanbad, Jharkhand, India 2Departamento de Física, Universidade Federal de Pernambuco, 50670-901 Recife, Pernambuco, Brazil 3Equipe Verres et Céramiques-UMR 6226 Sciences Chimiques de Rennes, Université de Rennes 1, 35042 Rennes Cedex, France 4Laboratório dos Materiais Fotônicos, Instituto de Química, UNESP, 14800-900 Araraquara, São Paulo, Brazil �Received 10 September 2009; accepted 7 October 2009; published online 20 November 2009� Optical properties of a neodymium �Nd3+� doped glass having composition based on the �Ga2S3�– �GeS2� system are reported. Transition probabilities, radiative lifetimes, and branching ratios related to Nd3+ levels were determined. Frequency upconversion �UC� luminescence due to nonresonant excitation at 1064 nm was observed at �535, �600, and �670 nm. The dependence of the UC intensity on the laser intensity and on the Nd3+ concentration as well as the dynamics of the luminescence process were studied. The results indicate that two-photon absorption by isolated Nd3+ ions and energy transfer among pairs of Nd3+ ions contribute to the UC luminescence. © 2009 American Institute of Physics. �doi:10.1063/1.3259439� I. INTRODUCTION Since the development of the first rare-earth �RE� ion laser1 many crystalline and glassy systems have been inves- tigated due to the influence of host materials on the lasing properties of the triply ionized RE ion. In particular, special glasses are being increasingly studied due to some peculiari- ties such as their large optical homogeneity, wide transpar- ency from the visible to the infrared region, and simple fab- rication procedures for obtaining good optical quality samples. The systems of main interest are those having low energy phonons because the quantum efficiency for RE ions luminescence is enhanced, allowing the development of more efficient lasers, optical amplifiers, and upconverters.2,3 Other important characteristics are the high mechanical strength and high chemical resistance of host glasses.4–12 Materials that present ideal characteristics for photonics are the chalcogenide glasses �based on S, Se, and Te�. They exhibit high refractive index, low cutoff phonon energy, and high stability against moisture and devitrification. The high linear refractive index contributes to the increase in the local field on the hosted RE ion and therefore large radiative tran- sition probabilities may be observed. In particular, glasses based on the �Ga2S3�– �GeS2� pseudobinary system have low cutoff phonon energies �300–400 cm−1�, show high RE ion solubility, and present large optical band gap. One important example is the composition Ga10Ge25S65 �GGS� due to its good chemical durability, large thermal stability, high refrac- tive index ��2.2�, and broad transmission window in the 0.5–12 �m region.13–15 The aim of the present work is the study of the linear optical characteristics and the infrared-to-visible frequency upconversion �UC� process in GGS glass doped with neody- mium �Nd3+� ions. Transition probabilities, radiative life- times, and branching ratios associated with the Nd3+ levels were determined by linear absorption spectroscopy and using the Judd–Ofelt �JO� theory.16,17 UC experiments were made by exciting the samples with a laser operating at 1064 nm �out of resonance with transitions starting from the ground state�. The mechanisms leading to the UC emissions in the green, orange, and red regions as well as the dynamics of the process are investigated. II. EXPERIMENTAL DETAILS The samples were prepared by the melting-quenching method. Three compositions were prepared for the present study: �Ga10Ge25S65�99.95–Nd0.05 �sample A�, �Ga10Ge25S65�99.9–Nd0.1 �sample B�, and �Ga10Ge25S65�99.75–Nd0.25 �sample C�. High purity polycrys- talline germanium �5N�, gallium �5N�, sulfur �5N�, and Nd �4N� were used for the synthesis. The elements were weighted and introduced into a silica tube having 10 mm inner diameter; vacuum of about 10−4 mbar was achieved in the tube before being sealed. The ampoule was then intro- duced in a rocking tubular furnace and slowly heated up to 900 °C to allow thorough reaction of the starting compounds and to avoid explosion due to the high vapor pressure of sulfides. The batch was homogenized for 8 h at this tempera- ture. Then, the rocking was stopped and the ampoule kept in the vertical position for 20 min to reduce the formation of bubbles in the glass. The ampoule was taken off the furnace, quenched in water at room temperature, and annealed at 370 °C for 3 h to reduce the internal stress caused by the quenching. Then the silica ampoule was opened; the ob- tained glass rod with �4 cm length and 10 mm diameter was removed and cut into slices of 2 mm thickness. Finally, a�Author to whom correspondence should be addressed. Electronic mail: cid@df.ufpe.br. JOURNAL OF APPLIED PHYSICS 106, 103512 �2009� 0021-8979/2009/106�10�/103512/5/$25.00 © 2009 American Institute of Physics106, 103512-1 Downloaded 11 Jul 2013 to 186.217.234.138. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jap.aip.org/about/rights_and_permissions http://dx.doi.org/10.1063/1.3259439 http://dx.doi.org/10.1063/1.3259439 http://dx.doi.org/10.1063/1.3259439 the samples were polished to obtain two parallel and two perpendicular polished faces for the optical measurements. Samples with dimensions of �10 mm diameter and 2.2 mm thickness were used in the optical experiments. A more de- tailed description of the fabrication procedure is presented in Ref. 15. The optical absorption experiments were made using a double-beam spectrophotometer. For the luminescence ex- periments a neodymium doped yttrium aluminum garnet la- ser operating at 1064 nm with pulses of �7 ns at 5 Hz was used. The linearly polarized laser beam was focused onto the sample with a 5 cm focal length lens, and the luminescence was collected in a direction perpendicular to the incident beam. The maximum intensity incident on the samples was �100 MW /cm2. The luminescence was analyzed by a 0.5 m spectrophotometer �resolution of 0.5 nm� attached to a pho- tomultiplier. The signals were recorded using a digital oscil- loscope connected to a computer. All measurements were made at room temperature. III. RESULTS AND DISCUSSION A. Optical characteristics Figure 1 shows the absorption spectrum of the Nd3+ �0.25 mol %� doped chalcogenide glass sample. Absorption bands were observed at �884, �806, �795, �750, �682, �594, and �532 nm corresponding to the transitions from the ground state �4I9/2� to the excited states 4F3/2, 4F5/2, 2H9/2, 4F7/2, 4F9/2, 4F5/2, and 4G7/2, respectively. The band positions are in agreement with the values observed in the other Nd3+ doped glasses.18 All transitions are inhomogeneously broad- ened due to site-to-site variations in the crystal field. The spectra of the other samples are similar but the intensity of the absorption bands depends linearly on the concentration of the Nd3+ ions. A simplified energy level scheme of the Nd3+ electronic levels is shown in Fig. 2. Oscillator strengths for different transitions on the basis of the observed absorption spectrum were determined using the JO theory. The calculated JO pa- rameters were used to determine physical quantities such as transition probabilities, branching ratios, and radiative life- times associated with various Nd3+ levels. The experimental oscillator strength is determined by the expression Fexpt=mc2n2 /�e2N��k���d�, where m is the elec- tron mass, c is the speed of light in vacuum, e is the electron charge, n is the index of refraction, �= �n2+2�2 /9n is the local field correction factor for electric-dipole transitions, N is the concentration of Nd3+ ions, and �k���d� is the inte- grated absorption coefficient.18 According to the JO theory, the oscillator strength for an electric-dipole allowed transition between the manifolds �S, L, J� and �S�, L�, J�� is given by Ftheor = 8�2m�̄� 3h�2J + 1� � �=2,4,6 �� �S,L,J� U� �S�,L�,J��� 2, where �̄ is the mean frequency between the two manifolds �in cm−1�, J is the total angular momentum, h is Planck’s constant, and �S ,L ,J� U� �S� ,L� ,J�� is the reduced dipole matrix element that is independent of the host environment. �� ��=2,3 ,4� are the JO intensity parameters that are sen- sitive to the host environment, to the separation between the energy levels involved, and to the closest electronic configu- ration having opposite parity. The spontaneous emission probability between the mani- folds �S, L, J� and �S�, L�, J�� is given by AJJ� = �64�4� /3h�2J+1��3�SED, where SED is the electric-dipole strength that is determined using the expression SED��S,L,J�;�S�,L�,J��� = e2 � �=2,4,6 �� �S,L,J� U� � �S�,L�,J��� 2. The magnetic-dipole strength assumes values that are two orders of magnitude smaller than SED and was neglected in the present calculations. The �� parameters were calculated using the experimen- tally observed oscillator strengths for the different transi- tions. The obtained values were �2=21.5�10−21 cm2, �4 600 800 1000 1200 0 2 4 6 4 F 7 /2 , 4 S 3 /2 4 F 9 /2 4 G 5 /2 2 K 1 3 /2 , 4 G 7 /2 A b s o rp ti o n s p e c tr u m (a rb it ra ry u n it s ) Wavelength (nm) 0.25mol% 4F5/2, 2H9/2 4F3/2 FIG. 1. Absorption spectrum of the �Ga10Ge25S65�99.75–Nd0.25 sample. 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 E n e r g y ( c m -1 ) 4 G7/2 4 G5/2 4 F9/24 F7/2, 4 S3/2 4 F5/2, 2 H9/2 4 F3/2 4 I13/2 4 I11/2 4 I9/2 FIG. 2. �Color online� Simplified energy level scheme for the Nd3+ ions. Solid lines represent radiative transitions. Dashed lines correspond to cross- relaxation involving ET processes. 103512-2 Rai et al. J. Appl. Phys. 106, 103512 �2009� Downloaded 11 Jul 2013 to 186.217.234.138. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jap.aip.org/about/rights_and_permissions =35.6�10−21 cm2, and �6=59.2�10−21 cm2 with a root- mean-square deviation �rms= 3.79�10−6. The theoretical values determined for the oscillator strengths using the val- ues obtained for �� ��=2, 4 , 6� are in reasonable agree- ment with the experimental results, as shown in Table I. The radiative lifetimes of the excited states were calcu- lated by R= ��J�AJJ�� −1, and the branching ratios for emis- sion from level J to J� were calculated by �JJ�=AJJ� R. The calculated values are given in Table II. B. Infrared-to-visible frequency UC The UC spectrum observed under infrared excitation at 1064 nm is shown in Fig. 3. Three luminescence bands are observed at �535, �600, and �670 nm corresponding to transitions 4G7/2→ 4I9/2, �4G7/2→ 4I11/2 ; 4G5/2→ 4I9/2�, and �4G7/2→ 4I13/2 ; 4G5/2→ 4I11/2�, respectively. To determine the number of photons and ions participat- ing in the UC process, the UC intensity was measured as a function of the laser power and as a function of the Nd3+ concentration. In Fig. 4�a� a quadratic dependence of the UC intensity on the pump power can be observed, indicating that two laser photons contribute to the emission of each UC photon. On the other hand, the log-log plot of the UC inten- sity as a function of the Nd3+ concentration, shown in Fig. 4�b�, presents a slope that varies from 1.59 to 1.75. This shows that more than one Nd3+ ion is involved in the exci- tation process of the UC emissions. To obtain more information about the UC process the temporal evolution of the 4G7/2→ 4I9/2 transition peaking at �535 nm was studied. The luminescence signal shows de- cay times of 53.4 0.4, 32.6 0.3, and 18.0 0.1 �s for Nd3+ concentrations of 0.05, 0.10, and 0.25 mol %, respec- tively, as shown in Figs. 5�a�–5�c�. Since the radiative life- time R of the 4G7/2 level is 81.23 �s �Table II� the mea- sured decay times indicate a strong interaction among the Nd3+ ions. We note that the energy difference �E�4G7/2� −E�4G5/2�� has about the same value as �E�4I11/2�−E�4I9/2��. Then the decrease in the lifetime of the 4G7/2 level is attrib- uted to the cross-relaxation process �4G7/2 ; 4I9/2� → �4G5/2 ; 4I11/2�. The actual lifetime is related to the cross- relaxation rate by = R / �1+WCR R� with WCR being equal to 6.4�103 s−1 �sample A�, 18�103 s−1 �sample B�, and 43 �103 s−1 �sample C�. In order to understand the origin of the UC luminescence we analyze three possible excitation pathways. We first note that the laser frequency �L is off resonance for a Nd3+ tran- sition starting from the ground state �4I9/2�. However, two- photon absorption �TPA� is resonant for a transition from the ground state to the 4G7/2 level. The UC luminescence inten- sity in this case would be quadratic with the laser intensity and would vary linearly with the Nd3+ concentration. Another possibility would be due to a one-photon tran- sition to level 4F3/2 followed by energy transfer �ET� be- tween pairs of excited Nd3+ ions. As a result of this process two ions excited to the 4F3/2 level may interact and exchange energy in such a way that one ion decays to the ground state TABLE I. Values of the theoretical and experimental oscillator strengths for Nd3+ ions in the GGS glass. Transitions E �cm−1� Fexpt ��10−6� Ftheor ��10−6� 4I9/2→ 4F3/2 11 315 5.86 4.83 4I9/2→ 4F5/2 ; 2H9/2 12 576 12.58 15.56 4I9/2→ 4F7/2 13 331 1.50 1.06 4I9/2→ 4F9/2 14 663 5.10 4.78 4I9/2→ 4G5/2 16 832 4.38 10.10 4I9/2→ 4G7/2 ; 2K13/2 18 797 3.64 3.30 TABLE II. Energy difference � E�, radiative transition probability �AJJ��, and branching ratio ��JJ�� between multiplets and radiative lifetime � R� for each state of Nd3+ ions. Transition E �cm−1� AJJ� �s−1� �JJ� R ��s� 4I11/2→ 4I9/2 2 110 43.43 1.0000 23 025.5 4I13/2→ 4I11/2 1 954 11.08 0.099 9 022.83 4I13/2→ 4I9/2 4 064 99.75 0.900 4F3/2→ 4I13/2 7 251 822.89 0.146 177.51 4F3/2→ 4I11/2 9 205 1 683.54 0.299 4F3/2→ 4I9/2 11 315 3 126.91 0.555 4F5/2→ 4F3/2 1 095 5.26 0.0003 69.54 4F5/2→ 4I13/2 8 346 2 330.91 0.162 4F5/2→ 4I11/2 10 300 4 381.28 0.305 4F5/2→ 4I9/2 12 410 7 663.11 0.533 2H9/2→ 4F5/2 166 0.0025 0.0000 480.22 2H9/2→ 4F3/2 1 261 1.11 0.0005 2H9/2→ 4I13/2 8 512 342.09 0.164 2H9/2→ 4I11/2 10 466 635.91 0.305 2H9/2→ 4I9/2 12 576 1 103.26 0.529 4F7/2→ 2H9/2 754 0.57 0.00009 163.18 4F7/2→ 4F5/2 920 1.04 0.00016 4F7/2→ 4F3/2 2 015 10.93 0.0018 4F7/2→ 4I13/2 9 266 1 063.11 0.173 4F7/2→ 4I11/2 11 220 1 887.48 0.308 4F7/2→ 4I9/2 13 330 3 165.15 0.516 4F9/2→ 2H9/2 1 333 0.54 0.0003 691.65 4F9/2→ 4F7/2 2 087 2.07 0.0014 4F9/2→ 4F5/2 2 253 2.59 0.0018 4F9/2→ 4F3/2 3 348 8.50 0.0058 4F9/2→ 4I13/2 10 599 269.75 0.186 4F9/2→ 4I11/2 12 553 448.14 0.309 4F9/2→ 4I9/2 14 663 714.23 0.493 4G5/2→ 2H9/2 2 169 46.51 0.0009 21.05 4G5/2→ 4F9/2 3 502 195.74 0.004 4G5/2→ 4F7/2 4 256 351.35 0.007 4G5/2→ 4F5/2 4 422 394.08 0.008 4G5/2→ 4F3/2 5 517 765.32 0.016 4G5/2→ 4I13/2 12 768 9 486.40 0.199 4G5/2→ 4I11/2 14 722 14 542.31 0.306 4G5/2→ 4I9/2 16 832 21 734.02 0.457 4G7/2→ 4G5/2 1 965 5.96 0.0005 81.23 4G7/2→ 2H9/2 4 134 55.58 0.0045 4G7/2→ 4F9/2 5 467 128.54 0.0104 4G7/2→ 4F7/2 6 221 189.39 0.0154 4G7/2→ 4F5/2 6 387 204.96 0.0166 4G7/2→ 4F3/2 7 482 329.49 0.0267 4G7/2→ 4I13/2 14 733 2 515.72 0.2043 4G7/2→ 4I11/2 16 687 3 655.66 0.2969 4G7/2→ 4I9/2 18 797 5 224.61 0.4244 103512-3 Rai et al. J. Appl. Phys. 106, 103512 �2009� Downloaded 11 Jul 2013 to 186.217.234.138. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jap.aip.org/about/rights_and_permissions and the other is promoted to the 4G7/2 level from where it decays radiatively to lower lying levels. However, although this process of ET has been observed in other glasses14,19 in the present case this process is not expected to be more ef- ficient than the TPA process discussed above because the one-photon frequency detuning for the electronic transition 4I9/2→ 4F3/2 is �1500 cm−1. The one-photon transition has to be phonon assisted requiring the participation of at least four phonons, and the corresponding probability is small. Another possibility to excite level 4F3/2 would be a resonant one-photon transition originating from level 4I11/2. However, the population in level 4I11/2 is small at 300 K. In both cases the UC luminescence intensity would present a quadratic de- pendence on the laser intensity �as in the TPA case� but the dependence on the Nd3+ concentration should be quadratic. Therefore the three UC pathways may originate a lumi- nescence signal that presents quadratic dependence with the laser intensity in agreement with the results of Fig. 4�a�. Concerning the dependence on the Nd3+ concentration, the simultaneous contribution of the three processes leads to a slope between 1 and 2 being in accord to Fig. 4�b�. Therefore we conclude that the three processes discussed contribute to the UC luminescence. IV. SUMMARY Radiative parameters of Nd3+ doped GGS glasses were determined from the optical absorption spectrum using the JO theory. The excitation of the samples at 1064 nm pro- duced frequency UC in the visible region. The experiments indicate that possible mechanisms contributing to the upcon- verted emissions are TPA from the ground state 4I9/2 to the 500 550 600 650 700 750 0.0 0.2 0.4 0.6 0.8 1.0 4G5/2 4I11/2 4G5/2 4I9/2 4G7/2 4I9/2 4G7/2 4I11/2 4G7/2 4I13/2 0.25 mol% U p c o n v e rs io n in te n s it y (a rb it ra ry u n it s ) Wavelength (nm) FIG. 3. Frequency UC spectrum for excitation using a laser operating at 1064 nm. Concentration of Nd3+ ions: 0.25 mol %. 8 9 20 30 40 50 60 708090 1 10 Slope~1.95±0.05 F re q u e n c y U p c o n v e rs io n in te n s it y (a rb it ra ry U n it s ) Laser intensity (MW/cm 2 ) (a) 0.05 0.1 0.15 0.2 0.25 0.1 1 10 slope~1,75±0,02 slope ~1,67±0,03 slope ~1,59±0,05 In te g ra te d in te n s it y (a rb it ra ry u n it s ) Concentration of Nd (mol%) (b) FIG. 4. �Color online� Dependence of the frequency UC signal on the laser intensity corresponding to the 4G7/2→ 4I9/2 transition for 0.25 mol % �a� and on the Nd3+ concentration �b�. Transitions: 4G7/2→ 4I9/2 �squares�, 4G7/2 → 4I11/2 �solid circles�, and 4G7/2→ 4I13/2 �triangles�. 0 50 100 150 200 0.01 0.1 1 In te g ra te d in te n s it y (a rb it ra ry u n it s ) Time (�s) (a) 0 20 40 60 80 0.01 0.1 1 In te g ra te d in te n s it y (a rb it ra ry u n it s ) Time (�s) (b) 0 20 40 60 80 100 120 0.01 0.1 1 In te g ra te d in te n s it y (a rb it ra ry u n it s ) Time (�s) (c) FIG. 5. �Color online� Temporal evolution of the UC signal due to the 4G7/2→ 4I9/2 transition. Samples with different values of Nd3+ concentration: �a� 0.05 mol %, �b� 0.10 mol %, and �c� 0.25 mol %. 103512-4 Rai et al. J. Appl. Phys. 106, 103512 �2009� Downloaded 11 Jul 2013 to 186.217.234.138. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jap.aip.org/about/rights_and_permissions 4G7/2 level involving isolated Nd3+ ions and one-photon ab- sorption to the 4F3/2 level followed by ET among pairs of Nd3+ excited to the 4F3/2 level. ACKNOWLEDGMENTS We acknowledge financial support from the Brazilian agencies Conselho Nacional de Desenvolvimento Científico e Tecnológico �CNPq�, the Fundação de Amparo à Ciência e Tecnologia de Pernambuco �FACEPE�, and the CAPES- COFECUB project �Contract No. 471/04�. 1E. Snitzer, Phys. Rev. Lett. 7, 444 �1961�. 2R. A. H. El-Mallawany, Tellurite Glasses Handbook—Physical Properties and Data �CRC, Boca Raton, FL, 2001�. 3J. S. Wang, E. M. Vogel, and E. Snitzer, Opt. Mater. �Amsterdam, Neth.� 3, 187 �1994�. 4M. Yamada, A. Mori, K. Kobayashi, H. Ono, T. Kanamori, K. Oikawa, K. Nishida, and Y. Ohishi, IEEE Photonics Technol. Lett. 10, 1244 �1998�. 5S. Q. Man, E. Y. B. Pun, and P. S. Chung, Opt. Commun. 168, 369 �1999�. 6A. Narazaki, K. Tanaka, K. Hirao, and N. Soga, J. Appl. Phys. 85, 2046 �1999�. 7V. K. Rai, Appl. Phys. B: Lasers Opt. 88, 297 �2007�. 8N. Jaba, A. Kanoun, H. Mejri, H. Maaref, and A. Brenier, J. Phys.: Con- dens. Matter 12, 7303 �2000�. 9F. Vetrone, J. C. Boyer, J. A. Capobianco, A. Speghini, and M. Bettinelli, Appl. Phys. Lett. 80, 1752 �2002�. 10S. Shen, A. Jha, L. Huang, and P. Joshi, Opt. Lett. 30, 1437 �2005�. 11Y. Ohishi, A. Mori, M. Yamada, H. Ono, Y. Nishida, and K. Oikawa, Opt. Lett. 23, 274 �1998�. 12Z. U. Borisiva, Chalcogenide Semiconductor Glasses �Leningrad Gos. University, Leningrad, 1983�. 13S. H. Messaddeq, V. R. Masteralo, M. S. Li, M. Tabackniks, D. Lezal, A. Ramos, and Y. Messaddeq, Appl. Surf. Sci. 205, 143 �2003�. 14V. K. Rai, C. B. de Araújo, Y. Ledemi, B. Bureau, M. Poulain, X. H. Zhang, and Y. Messaddeq, J. Appl. Phys. 103, 103526 �2008�. 15Y. Ledemi, “Verres et vitrocéramiques à base de chalco-halogénures dopés par des íons de terres rares pour la luminescence dans le visible,” Doctoral thesis, Université de Rennes, 2008. 16B. R. Judd, Phys. Rev. 127, 750 �1962�. 17G. S. Ofelt, J. Chem. Phys. 37, 511 �1962�. 18M. Yamane and Y. Asahara, Glasses for Photonics �Cambridge University Press, Cambridge, UK, 2000�. 19V. K. Rai, L. de S. Menezes, and C. B. de Araújo, J. Appl. Phys. 101, 123514 �2007�. 103512-5 Rai et al. J. Appl. Phys. 106, 103512 �2009� Downloaded 11 Jul 2013 to 186.217.234.138. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://jap.aip.org/about/rights_and_permissions http://dx.doi.org/10.1103/PhysRevLett.7.444 http://dx.doi.org/10.1016/0925-3467(94)90004-3 http://dx.doi.org/10.1109/68.705604 http://dx.doi.org/10.1016/S0030-4018(99)00374-0 http://dx.doi.org/10.1063/1.369500 http://dx.doi.org/10.1007/s00340-007-2717-4 http://dx.doi.org/10.1088/0953-8984/12/32/314 http://dx.doi.org/10.1088/0953-8984/12/32/314 http://dx.doi.org/10.1063/1.1458073 http://dx.doi.org/10.1364/OL.30.001437 http://dx.doi.org/10.1364/OL.23.000274 http://dx.doi.org/10.1364/OL.23.000274 http://dx.doi.org/10.1016/S0169-4332(02)01013-9 http://dx.doi.org/10.1063/1.2927402 http://dx.doi.org/10.1103/PhysRev.127.750 http://dx.doi.org/10.1063/1.1701366 http://dx.doi.org/10.1063/1.2745314