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Photoluminescence, photostructural transformations and photoinduced anisotropy in rare-earth-doped chalcogenide glassy films
Journal of Non-Crystalline Solids 352 (2006) 1599–1601 www.elsevier.com/locate/jnoncrysol
Photoluminescence, photostructural transformations and photoinduced anisotropy in rare-earth-doped chalcogenide glassy films V. Lyubin a
a,*
, M. Klebanov a, B. Sfez b, M. Veinger b, R. Dror b, I. Lyubina
c
Department of Physics, Ben-Gurion University, Prospect Ben-Gurion 1, 84105 Beer-Sheva, Israel b Electro-Optics Division, NRC Soreq, 81800 Yavne, Israel c Division of Applied Physics, Hebrew University, Jerusalem, Israel Available online 29 March 2006
Abstract Thin films fabricated by coevaporation in vacuum of chalcogenide glass and a rare-earth (RE) containing material are shown to have strong rare-earth photoluminescence, photostructural transformations and photoinduced anisotropy. The photoluminescence spectra of the films are similar to that of very different Nd- and Er-doped solids. Effects of concentration quenching of luminescence and luminescence fatigue are observed and studied. Using the photoresist effect of the doped films, binary diffraction gratings possessing strong IR photoluminescence were prepared. 2006 Elsevier B.V. All rights reserved. PACS: 71.55.Jv; 78.66.Jg; 78.55. m; 42.40.Eq Keywords: Vapor phase deposition; Chalcogenides; Luminescence; Photoinduced effects; Rare-earths in glasses
1. Introduction Chalcogenide glasses doped with RE ions, e.g., Er3+, Nd3+, Dy3+ or Pr3+ are attractive materials for a wide range of applications in fiber lasers and fiber amplifiers operating in the 1.2–1.7 lm wavelength range [1,2]. Because of such properties of chalcogenide glasses as high refractive index, transparency in the IR and photoinduced structural transformations (displayed in photodarkening, photorefraction and photoinduced dissolution [3,4]) together with low phonon energies, these materials may be the basis of many electro-optical devices. Photoluminescence in the RE-doped bulk chalcogenide glasses was studied in [5,6]. In many cases of practical application, it is necessary to have RE-doped thin chalcogenide films with efficient IR luminescence but this task encounters the problem of large differences in evaporation rates of chalcogenide glasses and
rare-earths, so that the usual thermal evaporation techniques cannot be applied. Therefore, some researchers used the radio frequency sputtering [7], ion implantation [8,9] and pulsed laser deposition [10,11] for the fabrication of RE-doped chalcogenide films. Unfortunately, in all cases some disadvantages were observed: low efficiency of luminescence, difficulty in fabrication of homogeneous films, and suppression of photoinduced structural transformations, which are very useful for many applications. In the present paper a new simple method for RE-doped film preparation, based on coevaporation in vacuum of chalcogenide glass and the RE containing material is proposed. The prepared films display simultaneously rareearth photoluminescence, photostructural transformations (photodarkening and photoresist effect) and photoinduced anisotropy. 2. Experimental
*
Corresponding author. Tel.: +972 8 6461249; fax: +972 8 6472903. E-mail addresses: [email protected] (V. Lyubin), [email protected] (M. Klebanov). 0022-3093/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2005.10.054
Thin Er- and Nd-doped As2S3 and As2Se3 films were fabricated by thermal coevaporation of starting crushed
V. Lyubin et al. / Journal of Non-Crystalline Solids 352 (2006) 1599–1601
chalcogenide glasses from quartz crucibles, and Er2S3 or Nd2S3 powder from a tungsten boat onto Corning-glass substrate in a vacuum of (1–3) · 10 6 Torr. Keeping a constant rate of RE-sulfide evaporation, the rate of chalcogenide glass evaporation was varied and samples with different Er or Nd concentration in the range of 0.3–1.8 wt% were fabricated. The thickness of the films was in the range 0.5–1.5 lm. Photoluminescence (PL) in the doped films was studied under Ar+ laser (k = 515 nm or k = 488 nm) light excitation. The light intensity was varied between 0.01 and 1.0 W/cm2. The PL, dispersed in wavelength by a spectrometer was detected by a liquid N2 cooled Ge photodiode. The exciting beam was chopped at a frequency of 170 Hz, and the signal from the photodiode was measured by a lock-in amplifier and recorded with a computer. Photostructural transformations (photodarkening and photoinduced anisotropy) were studied by using an installation with two linearly polarized Ar+ laser (488 nm, 10 mW) and He–Ne laser (633 nm, 0.1 mW) beams (inducing and probing beams) irradiating the same film area [12]. 3. Experimental results All RE-doped chalcogenide films retained the ability of photostructural transformations which are displayed both in the photodarkening and the photoresist effects. The photodarkening kinetics induced by an Ar+ laser in nondoped and Er-doped As2S3 films are shown in Fig. 1. The photoinduced anisotropy (birefringence) in the RE-doped As2S3 films had values up to 0.8–1.0%. To characterize the photoresist effect, the non-doped As2S3 film had a dissolution contrast c value (c is the ratio of dissolution rates for non-irradiated and irradiated areas of the film) equal 110, whilst the Nd-doped (1.3%) As2S3 films were characterized by c 47, which is also a sufficiently large value. The PL spectra with typical Er-ion emission for two Erdoped chalcogenide samples are shown in Fig. 2. Er-con-
1.6
Photo luminescence intensity (arb.un)
1600
1.2
1
0.8
2 0.4
0 1.44
1.48
1.52
1.56
1.6
1.64
Wavelength, (μm)
Fig. 2. Photoluminescence spectra in the Er-doped As2S3 (1) and As2Se3 (2) films excited by 0.1 W/cm2, 515 nm Ar-laser beam.
centration in the samples was 4%. Linear PL intensity dependence on the exciting laser beam intensity was observed. The PL spectra in Nd-doped As2S3 films with concentration of Nd in the range of 0.4–1.6 wt% indicated two maximums of luminescence, at 1080 nm and 900 nm (Fig. 3), which are typical for photoluminescence of very different Nd-doped solids [2,8]. Maximum values of luminescence intensity were observed at intermediate Nd concentration 0.8–1.3 wt%, further increases of Nd concentrations resulted in a decrease of the luminescence intensity. In all RE-doped films considerable luminescence fatigue was observed as can be seen in Fig. 4 for the case of Nddoped As2S3 film. It is important to note that initial values of luminescence intensity could not be restored after interruption of the exciting laser beam for 2–10 min (Fig. 4). A substantial photoresist effect permitted the use of the RE-doped films for fabrication of binary diffraction gratings of high resolution using our previous experience [13]. The SEM-picture of one such grating with a period of 200 nm, obtained in the Nd-doped As2S3 film, is shown in Fig. 5. These gratings were shown to have strong Ndphotoluminescence.
1
λ=488nm,P=10mW
1.6
0.6
Photoluminescence, (arb.units)
Transparency (rel. un)
0.8
(As-S)+Er
0.4
As-S 0.2
0 0
100
200
300
400
500
600
Time, (sec.)
Fig. 1. Kinetics of photodarkening for the non-doped and Er-doped As2S3 films.
1.2
0.8
0.4
0 800
900
1000
1100
1200
1300
Wavelength, (nm.)
Fig. 3. Typical photoluminescence spectrum in the Nd-doped As2S3 films excited by 0.02 W/cm2, 488 nm Ar-laser beam.
V. Lyubin et al. / Journal of Non-Crystalline Solids 352 (2006) 1599–1601 5
Photoluminescence, (arb.units)
4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 0
50
100
150
200
250
300
350
400
450
500
550
600
Excitation time, (sec.)
Fig. 4. Typical fatigue of photoluminescence in Nd-doped As2S3 film.
1601
is typical of many luminescent materials. Considerable luminescence fatigue is shown to be characteristic for fabricated films. The absence of restoration of fatigued luminescence after interruption of excitation allows us to explain the observed fatigue phenomenon differently from the mechanism of fatigue of low-temperature luminescence in bulk chalcogenide glasses, where initial values of luminescence intensity can be reestablished later, especially quickly with an increase of temperature [14,15]. It is probable that the observed luminescence fatigue is due to its excitation in the spectral range of light absorption in the chalcogenide glass and that direct excitation of RE atoms will result in the absence or essential decrease of the luminescence fatigue. Finally, it is important to stress the demonstrated possibility of using these films for the fabrication of diffraction gratings displaying essential RE photoluminescence. 5. Conclusion The results obtained in this work indicated that the method of coevaporation can be applied for the fabrication of different chalcogenide films doped by various RE elements, which are characterized by both efficient RE luminescence and essential photostructural transformations. High doping level of As2S3 and As2Se3 glassy films with Er3+ and Nd3+ ions was achieved using this method. It was also shown for the first time the possibility of fabricating diffraction gratings and probably some other electrooptical devices displaying essential RE photoluminescence. References
Fig. 5. SEM-picture of diffraction gratings produced in the Nd-doped As2S3 film.
4. Discussion The results obtained in this work indicate that the method of coevaporation of chalcogenide glass and the RE containing material can be applied for the fabrication of different chalcogenide films doped by various RE elements, which are characterized by both efficient RE luminescence and photostructural transformations with parameters similar to that in the non-doped films. The photoluminescence spectra for fabricated RE doped films are similar to that in very different Nd- and Er-doped solids. The observed concentration quenching of luminescence
[1] D.R. Simons, A.J. Faber, H. De Waal, Opt. Lett. 20 (1995) 468. [2] T. Schweizer, D.W. Hewak, D.N. Payne, T. Jensen, G. Huber, Electron. Lett 32 (1996) 666. [3] K. Tanaka, Rev. Solid State Sci. 4 (1990) 641. [4] V. Lyubin, M. Klebanov, A. Feigel, B. Sfez, Thin Solid Films 459 (2004) 183. [5] D.A. Turnbull, B.G. Aitken, S.G. Bishop, J. Non-Cryst. Solids 244 (1999) 260. [6] Z.G. Ivanova, Z. Aneva, Z. Cernosek, E. Cernoskova, V.S. Vasilev, J. Mat. Sci. Mat. Electron. 14 (2003) 761. [7] S. Ramachandran, S.G. Bishop, Appl. Phys. Lett. 73 (1998) 3196. [8] C. Meneghini, J.F. Viens, A. Villeneuve, E.J. Knystautas, M.A. Duguay, K.A. Richardson, J. Opt. Soc. Am. B 15 (1998) 1305. [9] Z.G. Ivanova, K. Koughia, D. Tonchev, J.C. Pivin, S.O. Kasap, J. Optoelectron. Adv. Mat. 7 (2005) 1271. [10] P. Ne˘mec, M. Frumar, B. Frumarova´, M. Jelı´nek, J. Lancˇok, J. Jedelsky´, Opt. Mat. 15 (2000) 191. [11] P.K. Dwivedi, Y.W. Sun, Y.Y. Tsui, D. Tonchev, M. Munzar, K. Koughia, C.J. Haugen, R.G. DeCorby, J.N. McMullin, S.O. Kasap, Appl. Surf. Sci. 248 (2005) 376. [12] V. Lyubin, M. Klebanov, Phys. Rev. B 53 (1996) R11924. [13] A. Feigel, M. Veinger, B. Sfez, A. Arsh, M. Klebanov, V. Lyubin, Appl. Phys. Lett. 83 (2003) 4480. [14] B.T. Kolomiets, T.N. Mamontova, V.V. Negreskul, Phys. Stat. Solid 27 (1968) K15. [15] J. Cernogora, F. Mollot, C. Benoit a la Guillaume, Phys. Stat. Solid 15 (1973) 401.
Photoluminescence, photostructural transformations and photoinduced anisotropy in rare-earth-doped chalcogenide glassy films V. Lyubin a
a,*
, M. Klebanov a, B. Sfez b, M. Veinger b, R. Dror b, I. Lyubina
c
Department of Physics, Ben-Gurion University, Prospect Ben-Gurion 1, 84105 Beer-Sheva, Israel b Electro-Optics Division, NRC Soreq, 81800 Yavne, Israel c Division of Applied Physics, Hebrew University, Jerusalem, Israel Available online 29 March 2006
Abstract Thin films fabricated by coevaporation in vacuum of chalcogenide glass and a rare-earth (RE) containing material are shown to have strong rare-earth photoluminescence, photostructural transformations and photoinduced anisotropy. The photoluminescence spectra of the films are similar to that of very different Nd- and Er-doped solids. Effects of concentration quenching of luminescence and luminescence fatigue are observed and studied. Using the photoresist effect of the doped films, binary diffraction gratings possessing strong IR photoluminescence were prepared. 2006 Elsevier B.V. All rights reserved. PACS: 71.55.Jv; 78.66.Jg; 78.55. m; 42.40.Eq Keywords: Vapor phase deposition; Chalcogenides; Luminescence; Photoinduced effects; Rare-earths in glasses
1. Introduction Chalcogenide glasses doped with RE ions, e.g., Er3+, Nd3+, Dy3+ or Pr3+ are attractive materials for a wide range of applications in fiber lasers and fiber amplifiers operating in the 1.2–1.7 lm wavelength range [1,2]. Because of such properties of chalcogenide glasses as high refractive index, transparency in the IR and photoinduced structural transformations (displayed in photodarkening, photorefraction and photoinduced dissolution [3,4]) together with low phonon energies, these materials may be the basis of many electro-optical devices. Photoluminescence in the RE-doped bulk chalcogenide glasses was studied in [5,6]. In many cases of practical application, it is necessary to have RE-doped thin chalcogenide films with efficient IR luminescence but this task encounters the problem of large differences in evaporation rates of chalcogenide glasses and
rare-earths, so that the usual thermal evaporation techniques cannot be applied. Therefore, some researchers used the radio frequency sputtering [7], ion implantation [8,9] and pulsed laser deposition [10,11] for the fabrication of RE-doped chalcogenide films. Unfortunately, in all cases some disadvantages were observed: low efficiency of luminescence, difficulty in fabrication of homogeneous films, and suppression of photoinduced structural transformations, which are very useful for many applications. In the present paper a new simple method for RE-doped film preparation, based on coevaporation in vacuum of chalcogenide glass and the RE containing material is proposed. The prepared films display simultaneously rareearth photoluminescence, photostructural transformations (photodarkening and photoresist effect) and photoinduced anisotropy. 2. Experimental
*
Corresponding author. Tel.: +972 8 6461249; fax: +972 8 6472903. E-mail addresses: [email protected] (V. Lyubin), [email protected] (M. Klebanov). 0022-3093/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2005.10.054
Thin Er- and Nd-doped As2S3 and As2Se3 films were fabricated by thermal coevaporation of starting crushed
V. Lyubin et al. / Journal of Non-Crystalline Solids 352 (2006) 1599–1601
chalcogenide glasses from quartz crucibles, and Er2S3 or Nd2S3 powder from a tungsten boat onto Corning-glass substrate in a vacuum of (1–3) · 10 6 Torr. Keeping a constant rate of RE-sulfide evaporation, the rate of chalcogenide glass evaporation was varied and samples with different Er or Nd concentration in the range of 0.3–1.8 wt% were fabricated. The thickness of the films was in the range 0.5–1.5 lm. Photoluminescence (PL) in the doped films was studied under Ar+ laser (k = 515 nm or k = 488 nm) light excitation. The light intensity was varied between 0.01 and 1.0 W/cm2. The PL, dispersed in wavelength by a spectrometer was detected by a liquid N2 cooled Ge photodiode. The exciting beam was chopped at a frequency of 170 Hz, and the signal from the photodiode was measured by a lock-in amplifier and recorded with a computer. Photostructural transformations (photodarkening and photoinduced anisotropy) were studied by using an installation with two linearly polarized Ar+ laser (488 nm, 10 mW) and He–Ne laser (633 nm, 0.1 mW) beams (inducing and probing beams) irradiating the same film area [12]. 3. Experimental results All RE-doped chalcogenide films retained the ability of photostructural transformations which are displayed both in the photodarkening and the photoresist effects. The photodarkening kinetics induced by an Ar+ laser in nondoped and Er-doped As2S3 films are shown in Fig. 1. The photoinduced anisotropy (birefringence) in the RE-doped As2S3 films had values up to 0.8–1.0%. To characterize the photoresist effect, the non-doped As2S3 film had a dissolution contrast c value (c is the ratio of dissolution rates for non-irradiated and irradiated areas of the film) equal 110, whilst the Nd-doped (1.3%) As2S3 films were characterized by c 47, which is also a sufficiently large value. The PL spectra with typical Er-ion emission for two Erdoped chalcogenide samples are shown in Fig. 2. Er-con-
1.6
Photo luminescence intensity (arb.un)
1600
1.2
1
0.8
2 0.4
0 1.44
1.48
1.52
1.56
1.6
1.64
Wavelength, (μm)
Fig. 2. Photoluminescence spectra in the Er-doped As2S3 (1) and As2Se3 (2) films excited by 0.1 W/cm2, 515 nm Ar-laser beam.
centration in the samples was 4%. Linear PL intensity dependence on the exciting laser beam intensity was observed. The PL spectra in Nd-doped As2S3 films with concentration of Nd in the range of 0.4–1.6 wt% indicated two maximums of luminescence, at 1080 nm and 900 nm (Fig. 3), which are typical for photoluminescence of very different Nd-doped solids [2,8]. Maximum values of luminescence intensity were observed at intermediate Nd concentration 0.8–1.3 wt%, further increases of Nd concentrations resulted in a decrease of the luminescence intensity. In all RE-doped films considerable luminescence fatigue was observed as can be seen in Fig. 4 for the case of Nddoped As2S3 film. It is important to note that initial values of luminescence intensity could not be restored after interruption of the exciting laser beam for 2–10 min (Fig. 4). A substantial photoresist effect permitted the use of the RE-doped films for fabrication of binary diffraction gratings of high resolution using our previous experience [13]. The SEM-picture of one such grating with a period of 200 nm, obtained in the Nd-doped As2S3 film, is shown in Fig. 5. These gratings were shown to have strong Ndphotoluminescence.
1
λ=488nm,P=10mW
1.6
0.6
Photoluminescence, (arb.units)
Transparency (rel. un)
0.8
(As-S)+Er
0.4
As-S 0.2
0 0
100
200
300
400
500
600
Time, (sec.)
Fig. 1. Kinetics of photodarkening for the non-doped and Er-doped As2S3 films.
1.2
0.8
0.4
0 800
900
1000
1100
1200
1300
Wavelength, (nm.)
Fig. 3. Typical photoluminescence spectrum in the Nd-doped As2S3 films excited by 0.02 W/cm2, 488 nm Ar-laser beam.
V. Lyubin et al. / Journal of Non-Crystalline Solids 352 (2006) 1599–1601 5
Photoluminescence, (arb.units)
4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 0
50
100
150
200
250
300
350
400
450
500
550
600
Excitation time, (sec.)
Fig. 4. Typical fatigue of photoluminescence in Nd-doped As2S3 film.
1601
is typical of many luminescent materials. Considerable luminescence fatigue is shown to be characteristic for fabricated films. The absence of restoration of fatigued luminescence after interruption of excitation allows us to explain the observed fatigue phenomenon differently from the mechanism of fatigue of low-temperature luminescence in bulk chalcogenide glasses, where initial values of luminescence intensity can be reestablished later, especially quickly with an increase of temperature [14,15]. It is probable that the observed luminescence fatigue is due to its excitation in the spectral range of light absorption in the chalcogenide glass and that direct excitation of RE atoms will result in the absence or essential decrease of the luminescence fatigue. Finally, it is important to stress the demonstrated possibility of using these films for the fabrication of diffraction gratings displaying essential RE photoluminescence. 5. Conclusion The results obtained in this work indicated that the method of coevaporation can be applied for the fabrication of different chalcogenide films doped by various RE elements, which are characterized by both efficient RE luminescence and essential photostructural transformations. High doping level of As2S3 and As2Se3 glassy films with Er3+ and Nd3+ ions was achieved using this method. It was also shown for the first time the possibility of fabricating diffraction gratings and probably some other electrooptical devices displaying essential RE photoluminescence. References
Fig. 5. SEM-picture of diffraction gratings produced in the Nd-doped As2S3 film.
4. Discussion The results obtained in this work indicate that the method of coevaporation of chalcogenide glass and the RE containing material can be applied for the fabrication of different chalcogenide films doped by various RE elements, which are characterized by both efficient RE luminescence and photostructural transformations with parameters similar to that in the non-doped films. The photoluminescence spectra for fabricated RE doped films are similar to that in very different Nd- and Er-doped solids. The observed concentration quenching of luminescence
[1] D.R. Simons, A.J. Faber, H. De Waal, Opt. Lett. 20 (1995) 468. [2] T. Schweizer, D.W. Hewak, D.N. Payne, T. Jensen, G. Huber, Electron. Lett 32 (1996) 666. [3] K. Tanaka, Rev. Solid State Sci. 4 (1990) 641. [4] V. Lyubin, M. Klebanov, A. Feigel, B. Sfez, Thin Solid Films 459 (2004) 183. [5] D.A. Turnbull, B.G. Aitken, S.G. Bishop, J. Non-Cryst. Solids 244 (1999) 260. [6] Z.G. Ivanova, Z. Aneva, Z. Cernosek, E. Cernoskova, V.S. Vasilev, J. Mat. Sci. Mat. Electron. 14 (2003) 761. [7] S. Ramachandran, S.G. Bishop, Appl. Phys. Lett. 73 (1998) 3196. [8] C. Meneghini, J.F. Viens, A. Villeneuve, E.J. Knystautas, M.A. Duguay, K.A. Richardson, J. Opt. Soc. Am. B 15 (1998) 1305. [9] Z.G. Ivanova, K. Koughia, D. Tonchev, J.C. Pivin, S.O. Kasap, J. Optoelectron. Adv. Mat. 7 (2005) 1271. [10] P. Ne˘mec, M. Frumar, B. Frumarova´, M. Jelı´nek, J. Lancˇok, J. Jedelsky´, Opt. Mat. 15 (2000) 191. [11] P.K. Dwivedi, Y.W. Sun, Y.Y. Tsui, D. Tonchev, M. Munzar, K. Koughia, C.J. Haugen, R.G. DeCorby, J.N. McMullin, S.O. Kasap, Appl. Surf. Sci. 248 (2005) 376. [12] V. Lyubin, M. Klebanov, Phys. Rev. B 53 (1996) R11924. [13] A. Feigel, M. Veinger, B. Sfez, A. Arsh, M. Klebanov, V. Lyubin, Appl. Phys. Lett. 83 (2003) 4480. [14] B.T. Kolomiets, T.N. Mamontova, V.V. Negreskul, Phys. Stat. Solid 27 (1968) K15. [15] J. Cernogora, F. Mollot, C. Benoit a la Guillaume, Phys. Stat. Solid 15 (1973) 401.