- Email: [email protected]
Cooperative emission in Yb3+ : YAG planar epitaxial waveguides
Journal of Luminescence 94–95 (2001) 29–33
Cooperative emission in Yb3+ : YAG planar epitaxial waveguides M. Malinowskia,b,*, M. Kaczkana, R. Piramidowicza, Z. Frukaczb, J. Sarneckib a
Institute of Microelectronics and Optoelectronics PW, ul. Koszykowa 75, 00-662 Warsaw, Poland b ! Institute of Electronic Materials Technology, ul. Wolczynska 133, 01-919 Warsaw, Poland
Abstract Blue emission was observed in Yb3+ activated YAG planar waveguides obtained by the liquid phase epitaxy on YAG substrates and in bulk Yb3+ : YAG crystals under infrared excitation. Through the excitation and emission spectra, decay time measurements and excitation intensity dependence the process responsible for this antiStokes emission was assigned to the cooperative deexcitation of two Yb3+ ions. Theoretical cooperative emission spectrum and the cooperative luminescence rate of Yb3+ : YAG waveguide were calculated. r 2001 Elsevier Science B.V. All rights reserved. Keywords: Cooperative emission; Ytterbium ion; Yb3+ : YAG
1. Introduction Recent literature demonstrates enormous potential of laser diode pumped Yb3+ activated solid state laser materials [1,2]. Because of the simple electronic structure of Yb3+ ion, which consists of only two levels, such unfavorable processes like excited state absorption, up-conversion or crossrelaxation are not active. Another advantage of Yb3+, resulting from the strong electron–phonon coupling is the broad band character of the optical transitions [3]. Due to these unique features, high efficiency, high power, tunability and mode locking have been reported for InGaAs diode laser pumped Yb3+ lasers [2,4]. Among the recently *Corresponding author. Tel.: +48-22-6607783; fax: +48-226288740. E-mail addresses: [email protected], [email protected] (M. Malinowski).
studied Yb3+ laser systems are wave-guiding m-lasers [5] and planar lasers. Planar structures play an increasingly important role as active components for integrated optics and fiberoptic telecommunication. Due to the waveguide effect, resulting in a high optical power confinement, a very high unit gain, low thresholds and high efficiencies, compared to bulk laser media, have been observed [6,7]. Waveguides appear also to be most suitable for nonlinear effects such as frequency doubling [8] and up-conversion [9,10]. Among several solid-state laser media, Yb3+ doped YAG is a promising candidate for planar waveguide lasers which are fabricated by several techniques; liquid phase epitaxy [11], laser deposition [12], ion implantation [13] and thermal bonding [14]. Recently, Yb3+-doped YAG channel waveguide laser was proposed as pumping source for praseodymium-doped fiber amplifiers (PDFA) [15]. The high concentration of activator
0022-2313/01/$ - see front matter r 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 2 3 1 3 ( 0 1 ) 0 0 2 7 1 - X
30
M. Malinowski et al. / Journal of Luminescence 94–95 (2001) 29–33
required for operation of planar waveguide devices and waveguide effect itself, result in a high optical intensities within the small volume which increase the probability of neighboring ions being simultaneously excited. In the case of Yb3+ systems this ion–ion interaction could result in a cooperative emission [16,17] which has been also used to study ion-pair clustering in optical glasses [18,19]. There are also few reports on the cooperative effects in Yb3+ [20] and Yb3++Tb3+ [21] activated silica fibers. In this work, we report on cooperative emission in the Yb3+ : YAG planar waveguide.
2. Experimental methods YAG : 15 at% Yb3+ thin films on the h1 1 1i YAG substrates using the liquid phase epitaxy technique and Yb3+ activated YAG bulk crystals were grown. The realization of laser active waveguides on YAG substrate requires an increase of the refractive index of a thin layer by an amount of about 102. As the value of refractive index in YAG rises with Yb3+ concentration at about 2 104 per at% of Yb3+ [11], the additional substitution of aluminum by 10% of gallium (Ga) ions was used. As shown by the X-ray diffraction, such Y2.85Yb0.15Al4.9Ga0.1O12 films grown on YAG substrate exhibit low lattice mismatch and no further codoping to adjust the lattice was necessary. The thickness of the investigated here waveguide was 24 mm. All experiments were performed at 300 K using a Ti3+-sapphire laser as the IR tunable excitation source. The details of the experimental apparatus used have been described previously [10].
3. Results and discussion The room temperature emission spectrum of Yb3+ : YAG waveguide after cw excitation at 940 nm is presented in the upper part of Fig. 1. Pumping in the 900–1000 nm band resulted also in both, YAG : Yb3+ crystals and waveguide in the blue emission centered at 484 nm, presented in the lower part of Fig. 1. From Fig. 1 it is also seen that some of the visible emission peaks are exactly at
Fig. 1. Room temperature emission spectra of Yb3+ : YAG after 940 nm excitation (a) infra red emission of epitaxial waveguide, (b), anti-Stokes emission of epitaxial waveguide and (c) anti-Stokes emission of bulk crystal.
Fig. 2. Room temperature absorption spectrum (a) and excitation spectrum (b), monitoring the blue anti-Stokes emission at 484 nm, in Yb3+ : YAG waveguide.
half wavelength of the IR peaks. As Yb3+ has only one excited manifold located in the energy range of 10,000 cm1 the observed blue, anti-Stokes emission could result from the cooperative process corresponding to the simultaneous radiative relaxation of Yb3+ ion pair accompanied by emission of a visible photon [16–18]. In order to further study, this anti-Stokes emission excitation spectra, fluorescence decay curves and power dependence were registered and analyzed. Fig. 2 shows that the near IR excitation and absorption
M. Malinowski et al. / Journal of Luminescence 94–95 (2001) 29–33
spectra of the YAG : Yb3+ waveguide has the same form. Small differences in the relative peak intensities are probably due to reabsorption effect. Fig. 3 shows the 300 K decay profiles of the Stokes 1030 nm and anti-Stokes 484 nm emission in the waveguide following excitation at 940 nm. The IR decay was exponential, with the characteristic lifetime of 0.887 ms which is shorter than 0.915 ms measured in the 15% Yb3+ : YAG single crystal, the blue emission decay time was 0.451 ms with no observable rise time. The presence of Tm3+ impurity, which also emits in the 488 nm spectral range, was excluded on the basis of timeresolved spectroscopy and classical emission and absorption investigations of the sample. It is recognized [1,2] that in Yb3+ compounds the decay of the 2F5/2 state is predominantly radiative. In the absence of intermediate levels the concentration quenching is strongly reduced and large energy gap to the ground state makes phonon relaxation low probable. In Yb3+ : YAG this is illustrated by the lifetime values of 1.17 ms reported for 0.07 at% Yb3+ : YAG [22] and 0.664 ms observed in 100% crystal, that is in YbAG [23]. The 2F5/2 lifetime of 0.90 ms was recently reported for 50%Yb3+ : YAG thin film obtained by pulsed laser deposition [12]. Shortening of the fluorescence lifetime observed in this work probably results from the slight degradation of the crystalline quality of the waveguide due to the presence of Ga ions. The cooperative emission lifetime is nearly half of that of the IR luminescence, which is in agreement with the results of a rate equation model [24] for the cooperative Yb3+ process. N’ 2 ¼ WN1 2N2 =t2 XðN2 Þ2 ;
ð1Þ
where N1 and N2 are the population densities of the Yb3+ ions in the ground 2F7/2 and excited 2F5/2 states, respectively, W is the pump rate, t2 is the lifetime of the Yb3+ 2F5/2 state and X is the probability of the cooperative transfer. Under the assumption of weak cooperative emission X5W; the anti-Stokes intensity decay can be expressed as Icoop =ðN2 Þ2 =exp ð2t=t2 Þ; when the single Yb3+ ion infrared intensity decay is IIR =N2 =exp ðt=t2 Þ: The ratio of the integrated cooperative emission intensity to that of the IR
31
Fig. 3. Infrared and cooperative emission decay curves of Yb3+ : YAG waveguide, T ¼ 300 K.
one was measured and used to calculate the cooperative luminescence rate according to the relation [24] X ¼2
Icoop 1 : IIR Wt22
ð2Þ
With the determined earlier spectroscopic data we found X ¼ 0:29 s1 which is larger than experimental cooperative rate of 0.13 s1 reported for Yb3+ : CsCdBr3 [24] but comparable to the value of 0.37 s1 found in Yb3+ activated Gd3Ga5O12 crystal [25]. Evolution of the anti-Stokes luminescence intensity as a function of the absorbed IR pump power has been investigated. It was observed that at low pumping the anti-Stokes fluorescence shows a quadratic dependence on pumping power, at higher excitation densities however, over 2 105 W/cm2, blue intensity saturates. Similar behavior has been observed in Yb3+ doped silica fibers [20] and was explained by the growth of amplified spontaneous emission which creates an additional deexcitation channel for Yb3+ ions. Finally, the theoretical cooperative emission spectrum has been calculated by self-convolution of the IR one and is shown in Fig. 4. Some of the strongest cooperative lines have been assigned in Fig. 4 to the transitions of doubly excited 2F5/2(i,i) Yb3+ pairs. Published data on the Stark energy level values of Yb3+ in YAG, due to the wide-band structure of absorption spectra, are
32
AA
AD
AC AB
DD
cooperative emission intensity [a.u.]
CD BD CC BC BB
M. Malinowski et al. / Journal of Luminescence 94–95 (2001) 29–33
Yb G F E
GG FF EE
3+
2
F5/2
(a) D C B A
ditions of light guiding and high concentration of ytterbium make the process relatively efficient and observable even at low excitation powers. Ion clustering in YAG structure could not be excluded and will be the subject of further study.
2
F7/2
Acknowledgements This work was supported by the Polish–French program ‘‘Polonium’’. One of the authors (MM) wishes to thank Universite´ Blaise Pascal in Clermont-Ferrand for supporting him as a visiting professor.
(b)
References 19000
20000
21000
22000
E [1/cm] Fig. 4. Comparison of the (a) experimental and (b) calculated cooperative luminescence spectra of Yb3+ : YAG.
contradictory [1–3]. A good agreement between experiment and theory was obtained in this work using energy level positions of the 2F5/2 Yb3+ multiplet in YAG proposed by Lupei et al. [3]. In YAG the nearest distance between two Yb3+ ions, ( entering at Y3+ dodecahedral sites are 3.8 A. Assuming that ions are distributed uniformly the average separation between Yb3+ ions in ( This value is 15% : YAG crystal is Rav ¼ 7:8 A. ( larger than critical distances of the order of 5 A reported for dipole–dipole electrostatic interaction in glass [26]. Thus, observed in this work strong cooperative emission could be considered as a signature of ion pairing in YAG system which also confirms our earlier results YAG : Pr3+ [27].
4. Conclusions Cooperative emission of Yb3+ ions in YAG planar epitaxial waveguide have been characterized in terms of absorption, fluorescence and excitation spectra and fluorescence lifetimes. Con-
[1] W.F. Krupke, IEEE J. Selected Topics QE 6 (2000) 1287. [2] W.F. Krupke, Curr. Opin. Solid State Mater. Sci. 4 (1999) 197. [3] A. Lupei, V. Enaki, V. Lupei, C. Presura, A. Petraru, J. Alloys Compounds 275–277 (1998) 196. [4] E.C. Honea, R.J. Beach, S.C. Mitchell, J.A. Skidmore, M.A. Emanuel, S.B. Sutton, S.A. Payne, P.V. Avizonis, R.S. Monroe, D.G. Harris, Opt. Lett. 25 (2000) 805. [5] T. Taira, J. Saikawa, T. Kobayashi, R.L. Byer, IEEE J. Selected Topics QE 3 (1997) 100. [6] B. Ferrand, B. Chambaz, M. Couchaud, Opt. Mater. 11 (1999) 101. [7] E. Daran, D.P. Shepherd, T. Bhutta, C. Serrano, Electron. Lett. 35 (1999) 398. [8] A. Boudrioua, J.C. Loulergue, P. Moretti, B. Jacquier, G. Aka, D. Vivien, Opt. Lett. 24 (1999) 1299. [9] D.P. Shepherd, A.C. Large, T.J. Warburton, A.C. Tropper, D.C. Hanna, C. Borel, A. Rameix, Ph. Thony, B. Ferrand, S. Guy, B. Jacquier, M.F. Joubert, Proceedings of the CLEOEurope, Amsterdam, The Netherlands, CPD 1.8, 1994, p.15. [10] M. Malinowski, R. Piramidowicz, J. Sarnecki, W. Wolinski, J. Phys.: Condens. Matter. 10 (1998) 1. [11] D. Pelenc, B. Chambaz, I. Chartier, B. Ferrand, C. Wyon, D.P. Shepherd, D.C. Hanna, A.C. Large, A.C. Trooper, Opt. Commun. 115 (1995) 491. [12] T. Shimoda, Y. Ishida, K. Adachi, M. Obara, Opt. Commun. 194 (2001) 175. [13] D.C. Hanna, J.K. Jones, A.C. Large, D.P. Shepherd, A.C. Trooper, P.J. Chandler, M.J. Rodman, P.D. Townsend, L. Zhang, Opt. Commun. 99 (1993) 211. . [14] U. Griebner, R. Grunwald, H. Schonnagel, Opt. Commun. 164 (1999) 185. [15] N. Sugimoto, Y. Ohishi, Y. Katoh, A. Tate, M. Shimokozono, S. Sudo, Appl. Phys. Lett. 67 (1995) 582.
M. Malinowski et al. / Journal of Luminescence 94–95 (2001) 29–33 [16] E. Nakazawa, S. Shionoya, Phys. Rev. Lett. 25 (1970) 1710. [17] V.V. Ovsyankin, in: A.A. Kaplyanskii, R.M. Macfarlane (Eds.), Spectroscopy of Solids Containing Rare Earth Ions, Elsevier, Amsterdam, 1987, p. 343, Chapter 7. [18] F. Auzel, D. Meichenin, F. Pell!e, P. Goldner, Opt. Mater. 4 (1994) 35. [19] B. Schaudel, P. Goldner, M. Prassas, F. Auzel, J. Alloys Compounds 300-301 (2000) 443. [20] Y. Ouerdane, S. Magne, M. Druetta, A. Boukenter, J.P. Goure, B. Jacquier, J. Phys. IV (1994) C4–545. [21] R.S. Brown, W.S. Brocklesby, W.L. Barnes, J.E. Townsend, J. Lumin. 63 (1995) 1.
33
[22] T.T. Basiev, Yu.K. Voronko, I.S. Shcherbakov, Sov. Phys. JETP 39 (1974) 1042. [23] F.D. Patel, E.C. Honea, J. Speth, S.A. Payne, R. Hutcheson, R. Equall, IEEE J. Quantum Electron. 37 (2001) 135. [24] Ph. Goldner, F. Pell!e, D. Meichenin, F. Auzel, J. Lumin. 71 (1997) 137. [25] L.C. Courrol, R.C. Samad, C. Madej, Ann. Braz. Commission Opt. 2 (2000) 102. [26] F. Auzel, P. Goldner, Opt. Matter. 16 (2001) 93. [27] M. Malinowski, P. Szczepanski, W. Wolinski, R. Wolski, Z. Frukacz, J. Phys.: Condens. Matter. 5 (1993) 6469.
Cooperative emission in Yb3+ : YAG planar epitaxial waveguides M. Malinowskia,b,*, M. Kaczkana, R. Piramidowicza, Z. Frukaczb, J. Sarneckib a
Institute of Microelectronics and Optoelectronics PW, ul. Koszykowa 75, 00-662 Warsaw, Poland b ! Institute of Electronic Materials Technology, ul. Wolczynska 133, 01-919 Warsaw, Poland
Abstract Blue emission was observed in Yb3+ activated YAG planar waveguides obtained by the liquid phase epitaxy on YAG substrates and in bulk Yb3+ : YAG crystals under infrared excitation. Through the excitation and emission spectra, decay time measurements and excitation intensity dependence the process responsible for this antiStokes emission was assigned to the cooperative deexcitation of two Yb3+ ions. Theoretical cooperative emission spectrum and the cooperative luminescence rate of Yb3+ : YAG waveguide were calculated. r 2001 Elsevier Science B.V. All rights reserved. Keywords: Cooperative emission; Ytterbium ion; Yb3+ : YAG
1. Introduction Recent literature demonstrates enormous potential of laser diode pumped Yb3+ activated solid state laser materials [1,2]. Because of the simple electronic structure of Yb3+ ion, which consists of only two levels, such unfavorable processes like excited state absorption, up-conversion or crossrelaxation are not active. Another advantage of Yb3+, resulting from the strong electron–phonon coupling is the broad band character of the optical transitions [3]. Due to these unique features, high efficiency, high power, tunability and mode locking have been reported for InGaAs diode laser pumped Yb3+ lasers [2,4]. Among the recently *Corresponding author. Tel.: +48-22-6607783; fax: +48-226288740. E-mail addresses: [email protected], [email protected] (M. Malinowski).
studied Yb3+ laser systems are wave-guiding m-lasers [5] and planar lasers. Planar structures play an increasingly important role as active components for integrated optics and fiberoptic telecommunication. Due to the waveguide effect, resulting in a high optical power confinement, a very high unit gain, low thresholds and high efficiencies, compared to bulk laser media, have been observed [6,7]. Waveguides appear also to be most suitable for nonlinear effects such as frequency doubling [8] and up-conversion [9,10]. Among several solid-state laser media, Yb3+ doped YAG is a promising candidate for planar waveguide lasers which are fabricated by several techniques; liquid phase epitaxy [11], laser deposition [12], ion implantation [13] and thermal bonding [14]. Recently, Yb3+-doped YAG channel waveguide laser was proposed as pumping source for praseodymium-doped fiber amplifiers (PDFA) [15]. The high concentration of activator
0022-2313/01/$ - see front matter r 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 2 3 1 3 ( 0 1 ) 0 0 2 7 1 - X
30
M. Malinowski et al. / Journal of Luminescence 94–95 (2001) 29–33
required for operation of planar waveguide devices and waveguide effect itself, result in a high optical intensities within the small volume which increase the probability of neighboring ions being simultaneously excited. In the case of Yb3+ systems this ion–ion interaction could result in a cooperative emission [16,17] which has been also used to study ion-pair clustering in optical glasses [18,19]. There are also few reports on the cooperative effects in Yb3+ [20] and Yb3++Tb3+ [21] activated silica fibers. In this work, we report on cooperative emission in the Yb3+ : YAG planar waveguide.
2. Experimental methods YAG : 15 at% Yb3+ thin films on the h1 1 1i YAG substrates using the liquid phase epitaxy technique and Yb3+ activated YAG bulk crystals were grown. The realization of laser active waveguides on YAG substrate requires an increase of the refractive index of a thin layer by an amount of about 102. As the value of refractive index in YAG rises with Yb3+ concentration at about 2 104 per at% of Yb3+ [11], the additional substitution of aluminum by 10% of gallium (Ga) ions was used. As shown by the X-ray diffraction, such Y2.85Yb0.15Al4.9Ga0.1O12 films grown on YAG substrate exhibit low lattice mismatch and no further codoping to adjust the lattice was necessary. The thickness of the investigated here waveguide was 24 mm. All experiments were performed at 300 K using a Ti3+-sapphire laser as the IR tunable excitation source. The details of the experimental apparatus used have been described previously [10].
3. Results and discussion The room temperature emission spectrum of Yb3+ : YAG waveguide after cw excitation at 940 nm is presented in the upper part of Fig. 1. Pumping in the 900–1000 nm band resulted also in both, YAG : Yb3+ crystals and waveguide in the blue emission centered at 484 nm, presented in the lower part of Fig. 1. From Fig. 1 it is also seen that some of the visible emission peaks are exactly at
Fig. 1. Room temperature emission spectra of Yb3+ : YAG after 940 nm excitation (a) infra red emission of epitaxial waveguide, (b), anti-Stokes emission of epitaxial waveguide and (c) anti-Stokes emission of bulk crystal.
Fig. 2. Room temperature absorption spectrum (a) and excitation spectrum (b), monitoring the blue anti-Stokes emission at 484 nm, in Yb3+ : YAG waveguide.
half wavelength of the IR peaks. As Yb3+ has only one excited manifold located in the energy range of 10,000 cm1 the observed blue, anti-Stokes emission could result from the cooperative process corresponding to the simultaneous radiative relaxation of Yb3+ ion pair accompanied by emission of a visible photon [16–18]. In order to further study, this anti-Stokes emission excitation spectra, fluorescence decay curves and power dependence were registered and analyzed. Fig. 2 shows that the near IR excitation and absorption
M. Malinowski et al. / Journal of Luminescence 94–95 (2001) 29–33
spectra of the YAG : Yb3+ waveguide has the same form. Small differences in the relative peak intensities are probably due to reabsorption effect. Fig. 3 shows the 300 K decay profiles of the Stokes 1030 nm and anti-Stokes 484 nm emission in the waveguide following excitation at 940 nm. The IR decay was exponential, with the characteristic lifetime of 0.887 ms which is shorter than 0.915 ms measured in the 15% Yb3+ : YAG single crystal, the blue emission decay time was 0.451 ms with no observable rise time. The presence of Tm3+ impurity, which also emits in the 488 nm spectral range, was excluded on the basis of timeresolved spectroscopy and classical emission and absorption investigations of the sample. It is recognized [1,2] that in Yb3+ compounds the decay of the 2F5/2 state is predominantly radiative. In the absence of intermediate levels the concentration quenching is strongly reduced and large energy gap to the ground state makes phonon relaxation low probable. In Yb3+ : YAG this is illustrated by the lifetime values of 1.17 ms reported for 0.07 at% Yb3+ : YAG [22] and 0.664 ms observed in 100% crystal, that is in YbAG [23]. The 2F5/2 lifetime of 0.90 ms was recently reported for 50%Yb3+ : YAG thin film obtained by pulsed laser deposition [12]. Shortening of the fluorescence lifetime observed in this work probably results from the slight degradation of the crystalline quality of the waveguide due to the presence of Ga ions. The cooperative emission lifetime is nearly half of that of the IR luminescence, which is in agreement with the results of a rate equation model [24] for the cooperative Yb3+ process. N’ 2 ¼ WN1 2N2 =t2 XðN2 Þ2 ;
ð1Þ
where N1 and N2 are the population densities of the Yb3+ ions in the ground 2F7/2 and excited 2F5/2 states, respectively, W is the pump rate, t2 is the lifetime of the Yb3+ 2F5/2 state and X is the probability of the cooperative transfer. Under the assumption of weak cooperative emission X5W; the anti-Stokes intensity decay can be expressed as Icoop =ðN2 Þ2 =exp ð2t=t2 Þ; when the single Yb3+ ion infrared intensity decay is IIR =N2 =exp ðt=t2 Þ: The ratio of the integrated cooperative emission intensity to that of the IR
31
Fig. 3. Infrared and cooperative emission decay curves of Yb3+ : YAG waveguide, T ¼ 300 K.
one was measured and used to calculate the cooperative luminescence rate according to the relation [24] X ¼2
Icoop 1 : IIR Wt22
ð2Þ
With the determined earlier spectroscopic data we found X ¼ 0:29 s1 which is larger than experimental cooperative rate of 0.13 s1 reported for Yb3+ : CsCdBr3 [24] but comparable to the value of 0.37 s1 found in Yb3+ activated Gd3Ga5O12 crystal [25]. Evolution of the anti-Stokes luminescence intensity as a function of the absorbed IR pump power has been investigated. It was observed that at low pumping the anti-Stokes fluorescence shows a quadratic dependence on pumping power, at higher excitation densities however, over 2 105 W/cm2, blue intensity saturates. Similar behavior has been observed in Yb3+ doped silica fibers [20] and was explained by the growth of amplified spontaneous emission which creates an additional deexcitation channel for Yb3+ ions. Finally, the theoretical cooperative emission spectrum has been calculated by self-convolution of the IR one and is shown in Fig. 4. Some of the strongest cooperative lines have been assigned in Fig. 4 to the transitions of doubly excited 2F5/2(i,i) Yb3+ pairs. Published data on the Stark energy level values of Yb3+ in YAG, due to the wide-band structure of absorption spectra, are
32
AA
AD
AC AB
DD
cooperative emission intensity [a.u.]
CD BD CC BC BB
M. Malinowski et al. / Journal of Luminescence 94–95 (2001) 29–33
Yb G F E
GG FF EE
3+
2
F5/2
(a) D C B A
ditions of light guiding and high concentration of ytterbium make the process relatively efficient and observable even at low excitation powers. Ion clustering in YAG structure could not be excluded and will be the subject of further study.
2
F7/2
Acknowledgements This work was supported by the Polish–French program ‘‘Polonium’’. One of the authors (MM) wishes to thank Universite´ Blaise Pascal in Clermont-Ferrand for supporting him as a visiting professor.
(b)
References 19000
20000
21000
22000
E [1/cm] Fig. 4. Comparison of the (a) experimental and (b) calculated cooperative luminescence spectra of Yb3+ : YAG.
contradictory [1–3]. A good agreement between experiment and theory was obtained in this work using energy level positions of the 2F5/2 Yb3+ multiplet in YAG proposed by Lupei et al. [3]. In YAG the nearest distance between two Yb3+ ions, ( entering at Y3+ dodecahedral sites are 3.8 A. Assuming that ions are distributed uniformly the average separation between Yb3+ ions in ( This value is 15% : YAG crystal is Rav ¼ 7:8 A. ( larger than critical distances of the order of 5 A reported for dipole–dipole electrostatic interaction in glass [26]. Thus, observed in this work strong cooperative emission could be considered as a signature of ion pairing in YAG system which also confirms our earlier results YAG : Pr3+ [27].
4. Conclusions Cooperative emission of Yb3+ ions in YAG planar epitaxial waveguide have been characterized in terms of absorption, fluorescence and excitation spectra and fluorescence lifetimes. Con-
[1] W.F. Krupke, IEEE J. Selected Topics QE 6 (2000) 1287. [2] W.F. Krupke, Curr. Opin. Solid State Mater. Sci. 4 (1999) 197. [3] A. Lupei, V. Enaki, V. Lupei, C. Presura, A. Petraru, J. Alloys Compounds 275–277 (1998) 196. [4] E.C. Honea, R.J. Beach, S.C. Mitchell, J.A. Skidmore, M.A. Emanuel, S.B. Sutton, S.A. Payne, P.V. Avizonis, R.S. Monroe, D.G. Harris, Opt. Lett. 25 (2000) 805. [5] T. Taira, J. Saikawa, T. Kobayashi, R.L. Byer, IEEE J. Selected Topics QE 3 (1997) 100. [6] B. Ferrand, B. Chambaz, M. Couchaud, Opt. Mater. 11 (1999) 101. [7] E. Daran, D.P. Shepherd, T. Bhutta, C. Serrano, Electron. Lett. 35 (1999) 398. [8] A. Boudrioua, J.C. Loulergue, P. Moretti, B. Jacquier, G. Aka, D. Vivien, Opt. Lett. 24 (1999) 1299. [9] D.P. Shepherd, A.C. Large, T.J. Warburton, A.C. Tropper, D.C. Hanna, C. Borel, A. Rameix, Ph. Thony, B. Ferrand, S. Guy, B. Jacquier, M.F. Joubert, Proceedings of the CLEOEurope, Amsterdam, The Netherlands, CPD 1.8, 1994, p.15. [10] M. Malinowski, R. Piramidowicz, J. Sarnecki, W. Wolinski, J. Phys.: Condens. Matter. 10 (1998) 1. [11] D. Pelenc, B. Chambaz, I. Chartier, B. Ferrand, C. Wyon, D.P. Shepherd, D.C. Hanna, A.C. Large, A.C. Trooper, Opt. Commun. 115 (1995) 491. [12] T. Shimoda, Y. Ishida, K. Adachi, M. Obara, Opt. Commun. 194 (2001) 175. [13] D.C. Hanna, J.K. Jones, A.C. Large, D.P. Shepherd, A.C. Trooper, P.J. Chandler, M.J. Rodman, P.D. Townsend, L. Zhang, Opt. Commun. 99 (1993) 211. . [14] U. Griebner, R. Grunwald, H. Schonnagel, Opt. Commun. 164 (1999) 185. [15] N. Sugimoto, Y. Ohishi, Y. Katoh, A. Tate, M. Shimokozono, S. Sudo, Appl. Phys. Lett. 67 (1995) 582.
M. Malinowski et al. / Journal of Luminescence 94–95 (2001) 29–33 [16] E. Nakazawa, S. Shionoya, Phys. Rev. Lett. 25 (1970) 1710. [17] V.V. Ovsyankin, in: A.A. Kaplyanskii, R.M. Macfarlane (Eds.), Spectroscopy of Solids Containing Rare Earth Ions, Elsevier, Amsterdam, 1987, p. 343, Chapter 7. [18] F. Auzel, D. Meichenin, F. Pell!e, P. Goldner, Opt. Mater. 4 (1994) 35. [19] B. Schaudel, P. Goldner, M. Prassas, F. Auzel, J. Alloys Compounds 300-301 (2000) 443. [20] Y. Ouerdane, S. Magne, M. Druetta, A. Boukenter, J.P. Goure, B. Jacquier, J. Phys. IV (1994) C4–545. [21] R.S. Brown, W.S. Brocklesby, W.L. Barnes, J.E. Townsend, J. Lumin. 63 (1995) 1.
33
[22] T.T. Basiev, Yu.K. Voronko, I.S. Shcherbakov, Sov. Phys. JETP 39 (1974) 1042. [23] F.D. Patel, E.C. Honea, J. Speth, S.A. Payne, R. Hutcheson, R. Equall, IEEE J. Quantum Electron. 37 (2001) 135. [24] Ph. Goldner, F. Pell!e, D. Meichenin, F. Auzel, J. Lumin. 71 (1997) 137. [25] L.C. Courrol, R.C. Samad, C. Madej, Ann. Braz. Commission Opt. 2 (2000) 102. [26] F. Auzel, P. Goldner, Opt. Matter. 16 (2001) 93. [27] M. Malinowski, P. Szczepanski, W. Wolinski, R. Wolski, Z. Frukacz, J. Phys.: Condens. Matter. 5 (1993) 6469.