Luminescence of Tb3+ doped TeO2–ZnO–Na2O–PbO glasses containing silver nanoparticles Luciana R. P. Kassab, Ricardo de Almeida, Davinson M. da Silva, and Cid B. de Araújo Citation: J. Appl. Phys. 104, 093531 (2008); doi: 10.1063/1.3010867 View online: http://dx.doi.org/10.1063/1.3010867 View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v104/i9 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. 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P. Kassab,1 Ricardo de Almeida,2 Davinson M. da Silva,2 and Cid B. de Araújo3,a� 1Laboratório de Vidros e Datação, CEETEPS/UNESP Faculdade de Tecnologia de São Paulo (FATEC-SP), 01124-060 São Paulo, Sao Paulo, Brazil 2Departamento de Engenharia de Sistemas Eletrônicos, Escola Politécnica da USP, 05508-900 São Paulo, Sao Paulo, Brazil 3Departamento de Física, Universidade Federal de Pernambuco, 50670-901 Recife, Pernambuco, Brazil �Received 1 August 2008; accepted 18 September 2008; published online 12 November 2008� Luminescence properties of Tb3+ doped TeO2–ZnO–Na2O–PbO glasses containing silver nanoparticles �NPs� were investigated. The absorption band due to the surface plasmon resonance in the NPs was observed. Its amplitude increases with the heat treatment of the samples that controls the nucleation of the NPs. Tb3+ emission bands centered at �485, �550, �585, and �623 nm were detected for excitation at 377 nm. The whole spectrum is intensified by the appropriate annealing time of the samples. Enhancement by �200% of the Tb3+ luminescence at 550 nm was observed for samples annealed at 270 °C during 62 h. This enhancement effect is due to the local field amplitude that increases with the amount of silver NPs and their aggregates. © 2008 American Institute of Physics. �DOI: 10.1063/1.3010867� I. INTRODUCTION The spectroscopic investigation of tellurite glasses con- taining silver nanoparticles �NPs� is of large interest because the optical properties of such composites can be controlled by appropriate thermal treatment. In general, tellurite based metal-dielectric composites present a large transmittance window �360–4500 nm�, low cutoff phonon energy ��700 cm−1�, high refractive index ��2.0�, and high non- linear optical response.1–11 Tellurite glasses and composites doped with Tb3+ ions deserve particular attention because they have large potential for the development of amplifiers and lasers covering the main telecom windows. In the visible region the emission spectrum of Tb3+ ion shows intense fluorescence in the blue- red region and this allows often the use of Tb3+ doped ma- terials as phosphors in fluorescent lamps, x-ray intensify screens, and TV tubes. The nucleation of silver and gold NPs in tellurite glasses was demonstrated recently.12–15 The growth of silver nano- structures in TeO2–PbO–GeO2 glass �labeled as TPG glass� originated large luminescence enhancement due to clusters with two or more Pb2+ ions.12 The influence of silver NPs on the luminescence efficiency of Pr3+ doped TPG glass was studied in Ref. 13. Enhanced Stokes luminescence and inten- sified frequency upconversion were observed for samples ex- cited in the visible region. Also recently the luminescence properties of Pr3+ doped TeO2–ZnO containing silver NPs and Eu3+ doped TPG with gold NPs were studied in Refs. 14 and 15. In all cases the presence of metallic nanostructures of silver or gold contributed to improve the luminescence char- acteristics of the samples. In the present work we report luminescence properties of TeO2–ZnO–Na2O–PbO glasses containing Tb3+ and silver NPs. It is shown that the luminescence in the blue-red region is enhanced due to the presence of silver NPs. In particular, the green emission at �550 nm is enhanced by �200%. The luminescence increase that occurs in the whole visible region is controlled by the heat treatment of the sample. II. EXPERIMENTAL DETAILS TeO2–ZnO–Na2O–PbO glasses were prepared with the starting composition 85.4 TeO2–6.97 ZnO–4.43 Na2O–3.20 PbO �in mole percent�. The doping species were Tb4O7 �5 wt %� and Ag2O �10 wt %�. The reagents were melted in a platinum crucible at 750 °C for 2 h, quenched in air in a heated brass mold, annealed for 2 h at 270 °C, and then cooled to room temperature inside the furnace. The samples were submitted to different heat-treatment times at 270 °C in order to reduce the Ag+ ions to Ag0 and to nucle- ate silver NPs. The amount of NPs increases with the in- crease in the annealing time. A 200 kV transmission electron microscope �TEM� was used to investigate the nucleation of NPs; their composition was verified by electron diffraction measurements. Absorp- tion spectra were recorded from 350 to 700 nm using a com- mercial spectrophotometer. For the photoluminescence mea- surements the samples were excited using a 30 W xenon lamp �pulses of �3 �s, 80 Hz�, and the obtained spectra, excited by radiation at 377 nm, were analyzed by a 0.25 m monochromator. The optical experiments were performed with the samples having dimensions of 10�10�2 mm3 at room temperature. a�Author to whom correspondence should be addressed. Electronic mail: cid@df.ufpe.br. JOURNAL OF APPLIED PHYSICS 104, 093531 �2008� 0021-8979/2008/104�9�/093531/3/$23.00 © 2008 American Institute of Physics104, 093531-1 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/10.1063/1.3010867 http://dx.doi.org/10.1063/1.3010867 http://dx.doi.org/10.1063/1.3010867 III. RESULTS AND DISCUSSION Figure 1 shows the absorption spectra of the Tb3+ doped TeO2–ZnO–Na2O–PbO samples, thermally treated at 270 °C during heat-treatment times �A=2, 17, 32, 47, and 62 h. The weak absorption feature at �480 nm is due to the 7F6→ 5D4 electronic transition of Tb3+ ions. The broadband centered at �490 nm is assigned to the surface plasmon resonance �SPR� associated to the NPs; its amplitude in- creases with increasing values of �A because the concentra- tion of the NPs grows as confirmed by TEM measurements. We recall that the SPR wavelength �SP depends on the size and shape of the NPs as well as on the dielectric constant of the host.2,16 In the present case �SP is located in the expected region and the large bandwidth is attributed to inhomoge- neous broadening due to the variety of NPs’ sizes and shapes. Figure 2 shows a TEM micrograph of a sample heat treated for 62 h demonstrating the presence of silver NPs and aggregates with dimensions in the range of 2–150 nm. Dif- fraction patterns characteristic of silver crystals were identi- fied. Similar results were obtained for samples heat treated for different values of �A. However, the amount of NPs in- creases with �A. The luminescence spectra of the Tb3+ doped metal- dielectric composite for excitation at 377 nm �7F6→ 5G5 transition� exhibit strong emission bands due to the 4f –4f transitions of Tb3+ ions. Figure 3�a� presents spectra corre- sponding to the transitions: 5D4→ 7F6 ��485 nm�, 5D4 → 7F5 ��550 nm�, 5D4→ 7F4 ��585 nm�, and 5D4→ 7F3 ��623 nm�. Because of the large energy gap between levels 5D4 and 7F0 ��17 300 cm−1� the quantum efficiency for lu- minescence originating from the 5D4 level is almost 100%. Luminescence transitions originating from the 5D3 level are not observed because of a cross-relaxation �5D3, 7F6� → �5D4, 7F0� among Tb3+ ions in the 5D3 level and neighbor ions in the ground state. This cross-relaxation process was observed in different glasses having Tb3+ concentration larger than 0.5%.17,18 The probability of multiphonon relax- ation among the 5D3 and 5D4 levels is very small because of the large energy gap ��5800 cm−1�. 400 450 500 550 600 650 700 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2 hours 17 hours 32 hours 47 hours 62 hours Wavelength (nm) A b s o rp ti o n s p e c tr a 5 D4 PLASMON Ag FIG. 1. �Color online� Absorption spectra of Tb3+ doped TeO2–ZnO–Na2O–PbO samples containing NPs for various heat-treatment times. FIG. 2. TEM image of the sample annealed during 62 h. The inset shows the electron diffraction pattern of the silver NPs. 480 500 520 540 560 580 600 620 640 0 20 40 60 80 2 hours 17 hours 32 hours 47 hours 62 hours Wavelength (nm) L u m in e s c e n c e in te n s it y (a rb it ra ry u n it s ) 5 D 4 - 7 F 6 5 D 4 - 7 F 5 5 D 4 - 7 F 4 5 D 4 - 7 F 3 (a) (b) FIG. 3. �Color online� �a� Emission spectra of Tb3+ doped TeO2–ZnO–Na2O–PbO samples containing silver NPs for different anneal- ing times �excitation wavelength: 377 nm�. �b� Simplified energy level scheme of Tb3+ ion with indication of the luminescence transitions ob- served. The dashed line indicates nonradiative decay to level 5D3 followed by cross-relaxation among excited ions and neighbors in the ground state according to �5D3; 7F6�→ �5D4; 7F0�. 093531-2 Kassab et al. J. Appl. Phys. 104, 093531 �2008� 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 A simplified energy level scheme for Tb3+ ions with in- dication of the emissions detected in the experiments is shown in Fig. 3�b�. The spectra in Fig. 3�a� correspond to various values of �A that correspond to different amounts of silver nanostruc- tures. It can be noted that there was an intensification of �200% for the luminescence signal centered at �550 nm, corresponding to �A=62 h, with respect to the sample heat treated during 2 h. We recall that previous studies with tel- lurite glass without metallic NPs14 indicate that the heat treatment under the present conditions does not change the symmetry around the trivalent rare-earth ions; the changes observed in Fig. 3�a� are attributed to the influence of the NPs that changes the local field in the Tb3+ ions location. Figure 3�a� allows the determination of the integrated intensity ratio R= I550 nm / I485 nm for different values of �A. The results are given in Fig. 4 which shows the behavior of R as a function of �A. We observe that the emission at �550 nm is more sensitive to the presence of silver NPs than the fluorescence band at �485 nm. This is due to the fact that electric dipole transitions are more sensitive to the local field change than magnetic dipole transitions. Similar results were obtained in Eu3+ doped tellurite glasses contain- ing gold NPs.15 It is also important to remark that luminescence en- hancement occurs even for the emissions centered at �585 and �623 nm. This is understood considering the influence of aggregates that usually originate hot spots of the electro- magnetic field19 that may originate the main contribution for intensification of the orange and red spectrum.13,14 This ef- fect was also reported for lead-germanate glasses.20 IV. SUMMARY In summary, the present results show that the nucleation of silver NPs in Tb3+ doped TeO2–ZnO–Na2O–PbO glass contributes for the enhancement of Tb3+ luminescence corre- sponding to wavelengths in the visible spectrum. The lumi- nescence enhancement is due to the local field growth that occurs because of the mismatch between the dielectric func- tion of the NPs and the host glass. The Tb3+ ions located in the vicinity of the NPs are in the presence of an intensified local field and consequently the luminescence efficiency in- creases. ACKNOWLEDGMENTS We acknowledge the financial support from the Con- selho Nacional de Desenvolvimento Científico e Tecnológico �CNPq� and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior �CAPES�. The Laboratório de Microscopia Eletrônica �IFUSP� are also acknowledged for the TEM im- ages. This work was performed under the Nanophotonics Network Program. 1Rare-Earth Doped Fiber Lasers and Amplifiers, edited by M. J. F. Digon- net �Marcel Dekker, New York, 1993�, and references therein. 2See, for instance, M. Yamane and Y. Asahara, Glasses for Photonics �Cambridge University Press, Cambridge, UK, 2000�. 3H. T. Amorim, M. V. D. Vermelho, A. S. Gouveia-Neto, F. C. Cassanges, S. J. L. Ribeiro, and Y. Messaddeq, J. Alloys Compd. 346, 282 �2002�. 4E. R. Taylor, N. N. Li, N. P. Sessions, and H. Buerger, J. Appl. Phys. 92, 112 �2002�. 5R. Rolli, M. Montagna, S. Chaussedent, A. Monteil, V. K. Tikhomirov, and M. Ferrari, Opt. Mater. �Amsterdam, Neth.� 21, 743 �2003�. 6P. Charton and P. Armand, J. Non-Cryst. Solids 316, 189 �2003�. 7J. Wu, S. Jiang, T. Qua, M. Kuwata-Gonokami, and N. Peyghambarian, Appl. Phys. Lett. 87, 211118 �2005�. 8G. S. Murugan, T. Susuki, and Y. Ohishi, Appl. Phys. Lett. 86, 161109 �2005�. 9V. K. Rai, L. de S. Menezes, and C. B. de Araújo, J. Appl. Phys. 102, 043505 �2007�. 10V. K. Rai, L. de S. Menezes, and C. B. de Araújo, Appl. Phys. A: Mater. Sci. Process. 91, 441 �2008�. 11W. S. Tsang, W. M. Yu, C. L. Mark, W. L. Tsui, K. W. Wong, and H. K. Hui, J. Appl. Phys. 91, 1871 �2002�. 12C. B. de Araújo, L. R. P. Kassab, R. A. Kobayashi, L. P. Naranjo, and P. A. S. Cruz, J. Appl. Phys. 99, 123522 �2006�. 13L. R. P. Kassab, C. B. de Araújo, R. A. Kobayashi, R. A. Pinto, and D. M. da Silva, J. Appl. Phys. 102, 103515 �2007�. 14V. K. Rai, L. de S. Menezes, C. B. de Araújo, L. R. P. Kassab, D. M. da Silva, and R. A. Kobayashi, J. Appl. Phys. 103, 093526 �2008�. 15R. de Almeida, D. M. da Silva, L. R. P. Kassab, and C. B. de Araújo, Opt. Commun. 281, 108 �2008�. 16P. N. Prasad, Nanophotonics �Wiley, New York, 2004�. 17D. de Graaf, S. J. Stelwagen, H. T. Hintzen, and G. de With, J. Non-Cryst. Solids 325, 29 �2003�. 18C. H. Kam and S. Buddhudu, Physica B �Amsterdam� 337, 237 �2003�. 19W. Wenseleers, F. Stellaci, T. Meyer-Friedrischsen, T. Mangel, C. A. Bauer, S. J. K. Pond, S. R. Marder, and J. W. Perry, J. Phys. Chem. B 106, 6853 �2002�. 20L. P. Naranjo, C. B. de Araújo, O. L. Malta, P. A. S. Cruz, and L. R. P. Kassab, Appl. Phys. Lett. 87, 241914 �2005�. 0 10 20 30 40 50 60 70 2.0 2.2 2.4 2.6 2.8 3.0 I 550nm /I 485nm N o rm a liz e d in te g ra te d in te n s it y ra ti o Heat - treatment time (hours) FIG. 4. �Color online� Normalized integrated intensity ratio between the luminescence at 550 and at 485 nm R= I550 nm / I485 nm as a function of the annealing time. 093531-3 Kassab et al. J. Appl. Phys. 104, 093531 �2008� 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/10.1016/S0925-8388(02)00513-3 http://dx.doi.org/10.1063/1.1483391 http://dx.doi.org/10.1016/S0925-3467(02)00092-7 http://dx.doi.org/10.1016/S0022-3093(02)01797-0 http://dx.doi.org/10.1063/1.2132532 http://dx.doi.org/10.1063/1.1906323 http://dx.doi.org/10.1063/1.2769788 http://dx.doi.org/10.1007/s00339-008-4421-6 http://dx.doi.org/10.1007/s00339-008-4421-6 http://dx.doi.org/10.1063/1.1429762 http://dx.doi.org/10.1063/1.2208288 http://dx.doi.org/10.1063/1.2817980 http://dx.doi.org/10.1063/1.2919566 http://dx.doi.org/10.1016/j.optcom.2007.08.072 http://dx.doi.org/10.1016/j.optcom.2007.08.072 http://dx.doi.org/10.1016/S0022-3093(03)00324-7 http://dx.doi.org/10.1016/S0022-3093(03)00324-7 http://dx.doi.org/10.1021/jp014675f http://dx.doi.org/10.1063/1.2143135