Charge Transfer Luminescence of Yb3+
Charge Transfer Luminescence of Yb3+ Charge Transfer Luminescence of Yb3+
192L. van Pieterson et al. / Journal of Luminescence 91 (2000) 177–193Fig. 18. Thermal quenching due to photoionization for a4f n ! 4f n1 5d transition (a) and for a CT transition (b). VB andCB are the valence band and conduction band, respectively,E e and E h represent the energy of an electron and a hole,respectively, RE=rare earth ion and L=ligand. The position ofthe excited CTS for Eu 3+ (broken line in (b)) is at slightly lowerenergies than for Yb 3+ (drawn line in (b)).levels are shown in an energy diagram as iscommonly used for semiconductors. In this pictureinformation on lattice relaxation in the excitedstate is lost. An alternative picture for photoionizationfrom a charge transfer state has beenused in Refs. [24,25], where a configurationalcoordinate diagram like Fig. 17 is shown. Thecharge transfer state, the ionized state and the freeelectron–hole pair are represented by parabolaewith a large (CT) or small (electron–hole) off-setwith respect to the ground state. In this representationthe information on relaxation is evident, butthe mobility of the charge carriers (holes in the VBor electrons in the CB) is less evident. Regardlessof which picture is used, one should always beaware of the limitations in each representation,especially when both localized and delocalizedprocesses are shown in one picture.Evidence supporting the explanation of quenchingby thermally activated photoionization comesfrom the results on the quenching of the Eu 3+emission under CT excitation. The Eu 3+ emission( 5 D 0 ! 7 F J ) under charge transfer excitationquenches at much higher temperatures. The lowerquenching temperature for the CT luminescencefrom Yb 3+ can be related to the lower stability ofYb 2+ compared to Eu 2+ (the most stable divalentlanthanide). In the excited CT state the lanthanideis (formally) 2+ and due to the lower stability ofYb 2+ the CTS will be closer to the valence bandand quenching due to photoionization can beexpected at lower temperatures.The order in quenching temperatures is similarfor Yb 3+ and Eu 3+ . In the host lattices whereEu 3+ is incorporated on a La 3+ -site, the quenchingtemperature is much lower than in latticeswhere Eu 3+ occupies a Sc 3+ or Y 3+ site. This is inagreement with the low-quenching temperature forYb 3+ in these lattices. In the host lattices with veryhigh-quenching temperatures for the Eu 3+ emissionunder charge transfer excitation, Yb 3+ CTluminescence is observed, but has a quenchingtemperature below room temperature. An exceptionis YBO 3 . In this lattice, the Eu 3+ luminescenceafter CT excitation quenches at very hightemperature (>850 K), but no Yb 3+ CT luminescenceis observed at all. In general, CT luminescencefrom Yb 3+ is only observed in host latticesin which the quenching temperature for Eu 3+ ishigher than about 500 K.An alternative explanation for the higherquenching temperatures of Eu 3+ compared toYb 3+ is that for Yb 3+ radiative decay from thecharge transfer state (t 150 ns) has to competewith non-radiative decay to the 2 F 5/2 and 2 F 7/2states. In Eu 3+ , fast non-radiative decay (t ps)to the 5 D states has to compete with non-radiativedecay to the ground state 7 F levels, and once the5 D 0 state is populated, radiative decay occurs. Atpresent, new experiments are planned to obtainbetter insight in the quenching mechanism.5. ConclusionsThe charge transfer luminescence of Yb 3+ hasbeen investigated in a large variety of host lattices.In some host lattices (LiYF 4 , orthophosphates,aluminates, oxides and oxysulfides) charge transferluminescence has been observed, while in otherhost lattices (orthoborates, oxyhalogenides) thecharge transfer luminescence is quenched even at10 K. Besides quenching due to cross-over fromthe CT excited state to the ground state, alsoindications for quenching by (thermally activated)photoionization have been obtained. Most likely,
L. van Pieterson et al. / Journal of Luminescence 91 (2000) 177–193 193the photoionization involves the escape of a holefrom the charge transfer state to the valence band.The position of the charge transfer absorptionand emission bands shifts to longer wavelengthswith increasing covalency of the host lattice andwith increasing size of the cation site. The radiativelifetime of the charge transfer emission is typicallybetween 100 and 200 ns, which is relatively long fora fully allowed transition. A comparison has beenmade with the luminescence of Eu 3+ . The chargetransfer absorption band is higher in energy forYb 3+ than for Eu 3+ in the same host lattice. Thereis a clear relation between the quenching temperatureof the Eu 3+ emission under CT excitation andthe CT emission from Yb 3+ . Only for host latticesin which the quenching temperature of the Eu 3+emission is higher than about 500 K charge transferluminescence from Yb 3+ could be observed,but this emission is already quenched below roomtemperature.AcknowledgementsThe authors are grateful to Dr. P. Gu¨ rtlerand Mr. S. Petersen from HASYLAB for theopportunity to use the excellent facilities for VUVspectroscopy at the DESY synchrotron, Hamburg(Germany) and their support whenever needed.The authors are also grateful to Mr. E. Mix andDr. S. Ku¨ ck of the ‘Institut fu¨ r Laser-physik’ of theUniversity of Hamburg for supplying the RE 2 O 3 ,YAlO 3 and YAG crystals. The financial support ofPhilips Lighting is gratefully acknowledged.References[1] G. Blasse, B.C. Grabmaier, Luminescent Materials,Springer, Berlin, 1994.[2] C.K. Jrgensen, Progr. Inorg. Chem. 12 (1970) 101.[3] E. Nakazawa, Chem. Phys. Lett. 56 (1978) 161.[4] E. Nakazawa, J. Lumin. 18/19 (1979) 272.[5] E. Danielson, M. Devenney, D.M. Giaquinta, J.H. Golden,R.C. Haushalter, E.W. McFarland, D.M. Poojary,C.M. Reaves, W.H. Weinberg, X. Di Wu, Science 279(1998) 837.[6] A.T. Aldred, Acta Crystallogr. B 40 (1984) 569.[7] G. Chadeyron, M. El-Ghozzi, R. Mahiou, A. Arbus,J.C. Cousseins, J. Solid State Chem. 128 (1997) 261.[8] M. Kottaisamy, R. Jagannathan, Ravi P. Rao,M. Avudaithai, L.K. Srinivasan, V. Sundaram, J. Electrochem.Soc. 142 (1995) 3205.[9] R.W.G. Wyckoff, Crystal Structures, 2nd Ed., vol. 1–3,Wiley, New York, 1960.[10] G. Blasse, J. Inorg. Nucl. Chem. 28 (1966) 2444.[11] F. Stewner, R. Hoppe, Z. Anorg. Allgem. Chem. 380(1971) 250.[12] R.E. Thoma, C.F. Weaver, H.A. Friedman, H. Insley,L.A. Harris, H.A. Yakel Jr., J. Phys. Chem. 65 (1961)1096.[13] L. Fornaseiro, E. Mix, V. Peters, K. Petermann, G. Huber,Cryst. Res. Technol. 34 (1999) 255.[14] E. Mix, L. Fornasiero, V. Peters, K. Petermann, G. Huber,Proceedings of the Twelfth International Conference onCrystal Growth, July 26–31, Jerusalem, 1998.[15] U. Hahn, N. Schwentner, G. Zimmerer, Nucl. Instrum.and Meth. 152 (1978) 261.[16] R.T. Wegh, H. Donker, A. Meijerink, Phys. Rev. B 56(1997) 13 841.[17] T. Tomiki, T. Shikenbaru, Y. Ganaha, T. Futemma,H. Kato, M. Yuri, H. Fukutani, T. Miyahara, S. Shin,M. Ishigame, J. Tamashiro, J. Phys. Soc. Japan 61 (1992)2951.[18] T. Szcezurek, M. Schlesinger, in: B. Jezowska-Trzebiatowska, J. Legendziewic, W. Strek (Eds.), RareEarths Spectroscopy, World Scientific, Singapore, 1985,p. 309.[19] C.K. Jrgensen, Modern Aspects of Ligand-Field Theory,North-Holland, Amsterdam, 1971.[20] N. Vugt, T. Wigmans, G. Blasse, J. Inorg. Nucl. Chem. 35(1973) 2602.[21] C.K. Jrgensen, Molec. Phys. 5 (1962) 271.[22] H.E. Hoefdraad, J. Solid State Chem. 15 (1975) 175.[23] R.D. Shannon, C.T. Prewitt, Acta Crystallogr. B 25 (1969)925.[24] C. Dujardin, B. Moine, C. Pedrini, J. Lumin. 54 (1993)259.[25] B. Moine, B. Courtois, C. Pedrini, J. Phys. (France) 50(1989) 2105.[26] T. Hoshina, S. Imanaga, S. Yokono, J. Lumin. 15 (1977)455.[27] C.W. Struck, W.H. Fonger, Phys. Rev. B 4 (1971) 22.
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L. van Pieterson et al. / Journal <strong>of</strong> <strong>Luminescence</strong> 91 (2000) 177–193 193the photoionization involves the escape <strong>of</strong> a holefrom the charge transfer state to the valence band.The position <strong>of</strong> the charge transfer absorptionand emission bands shifts to longer wavelengthswith increasing covalency <strong>of</strong> the host lattice andwith increasing size <strong>of</strong> the cation site. The radiativelifetime <strong>of</strong> the charge transfer emission is typicallybetween 100 and 200 ns, which is relatively long fora fully allowed transition. A comparison has beenmade with the luminescence <strong>of</strong> Eu 3+ . The chargetransfer absorption band is higher in energy forYb 3+ than for Eu 3+ in the same host lattice. Thereis a clear relation between the quenching temperature<strong>of</strong> the Eu 3+ emission under CT excitation andthe CT emission from Yb 3+ . Only for host latticesin which the quenching temperature <strong>of</strong> the Eu 3+emission is higher than about 500 K charge transferluminescence from Yb 3+ could be observed,but this emission is already quenched below roomtemperature.AcknowledgementsThe authors are grateful to Dr. P. Gu¨ rtlerand Mr. S. Petersen from HASYLAB for theopportunity to use the excellent facilities for VUVspectroscopy at the DESY synchrotron, Hamburg(Germany) and their support whenever needed.The authors are also grateful to Mr. E. Mix andDr. S. Ku¨ ck <strong>of</strong> the ‘Institut fu¨ r Laser-physik’ <strong>of</strong> theUniversity <strong>of</strong> Hamburg for supplying the RE 2 O 3 ,YAlO 3 and YAG crystals. The financial support <strong>of</strong>Philips Lighting is gratefully acknowledged.References[1] G. Blasse, B.C. Grabmaier, Luminescent Materials,Springer, Berlin, 1994.[2] C.K. Jrgensen, Progr. Inorg. Chem. 12 (1970) 101.[3] E. Nakazawa, Chem. Phys. Lett. 56 (1978) 161.[4] E. Nakazawa, J. Lumin. 18/19 (1979) 272.[5] E. Danielson, M. Devenney, D.M. Giaquinta, J.H. Golden,R.C. Haushalter, E.W. McFarland, D.M. Poojary,C.M. Reaves, W.H. Weinberg, X. Di Wu, Science 279(1998) 837.[6] A.T. Aldred, Acta Crystallogr. B 40 (1984) 569.[7] G. Chadeyron, M. El-Ghozzi, R. Mahiou, A. Arbus,J.C. Cousseins, J. Solid State Chem. 128 (1997) 261.[8] M. Kottaisamy, R. Jagannathan, Ravi P. Rao,M. Avudaithai, L.K. Srinivasan, V. Sundaram, J. Electrochem.Soc. 142 (1995) 3205.[9] R.W.G. Wyck<strong>of</strong>f, Crystal Structures, 2nd Ed., vol. 1–3,Wiley, New York, 1960.[10] G. Blasse, J. Inorg. Nucl. Chem. 28 (1966) 2444.[11] F. Stewner, R. Hoppe, Z. Anorg. Allgem. Chem. 380(1971) 250.[12] R.E. Thoma, C.F. Weaver, H.A. Friedman, H. Insley,L.A. Harris, H.A. Yakel Jr., J. Phys. Chem. 65 (1961)1096.[13] L. Fornaseiro, E. Mix, V. Peters, K. Petermann, G. Huber,Cryst. Res. Technol. 34 (1999) 255.[14] E. Mix, L. Fornasiero, V. Peters, K. Petermann, G. Huber,Proceedings <strong>of</strong> the Twelfth International Conference onCrystal Growth, July 26–31, Jerusalem, 1998.[15] U. Hahn, N. Schwentner, G. Zimmerer, Nucl. Instrum.and Meth. 152 (1978) 261.[16] R.T. Wegh, H. Donker, A. Meijerink, Phys. Rev. B 56(1997) 13 841.[17] T. Tomiki, T. Shikenbaru, Y. Ganaha, T. Futemma,H. Kato, M. Yuri, H. Fukutani, T. Miyahara, S. Shin,M. Ishigame, J. Tamashiro, J. Phys. Soc. Japan 61 (1992)2951.[18] T. Szcezurek, M. Schlesinger, in: B. Jezowska-Trzebiatowska, J. Legendziewic, W. Strek (Eds.), RareEarths Spectroscopy, World Scientific, Singapore, 1985,p. 309.[19] C.K. Jrgensen, Modern Aspects <strong>of</strong> Ligand-Field Theory,North-Holland, Amsterdam, 1971.[20] N. Vugt, T. Wigmans, G. Blasse, J. Inorg. Nucl. Chem. 35(1973) 2602.[21] C.K. Jrgensen, Molec. Phys. 5 (1962) 271.[22] H.E. Hoefdraad, J. Solid State Chem. 15 (1975) 175.[23] R.D. Shannon, C.T. Prewitt, Acta Crystallogr. B 25 (1969)925.[24] C. Dujardin, B. Moine, C. Pedrini, J. Lumin. 54 (1993)259.[25] B. Moine, B. Courtois, C. Pedrini, J. Phys. (France) 50(1989) 2105.[26] T. Hoshina, S. Imanaga, S. Yokono, J. Lumin. 15 (1977)455.[27] C.W. Struck, W.H. Fonger, Phys. Rev. B 4 (1971) 22.
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