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Effect of pressure on the luminescence properties of Nd3+ doped SrWO4 laser crystal
Journal of Alloys and Compounds 451 (2008) 212–214
Effect of pressure on the luminescence properties of Nd3+ doped SrWO4 laser crystal D. Errandonea a , Chaoyang Tu b,c , Guohua Jia b,c , I.R. Mart´ın d,∗ , U.R. Rodr´ıguez-Mendoza d , F. Lahoz d , M.E. Torres e , V. Lav´ın d a
Dpto. F´ısica Aplicada-ICMUV, Universitat de Val`encia, Edificio de Investigaci´on, c/Dr. Moliner 50, 46100 Burjassot, Valencia, Spain b Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China c Graduated School of Chinese Academy of Science, 100039 Beijing, China d Dpto. F´ısica Fundamental y Experimental, Electr´ onica y Sistemas, Univ. de La Laguna, Avda. Astrof. Fco. S´anchez, s/n La Laguna 38206, Spain e Dpto. F´ısica B´ asica, Univ. de La Laguna, Avda. Astrof. Fco. S´anchez, s/n La Laguna 38206, Spain Available online 18 April 2007
Abstract The luminescence spectra of the 4 F3/2 → 4 I9/2 transition of Nd3+ ions in a SrWO4 crystal have been analyzed as a function of pressure at room temperature. Experiments have been performed in a diamond-anvil cell up to 13 GPa. At around 10 GPa some changes in the emission spectra have been observed which are attributed to a structural phase transition of the SrWO4 matrix. These results are in good agreement with a previous paper, in which in a pure SrWO4 matrix a scheelite to fergusonite phase transition is found around 10.5 GPa. Moreover, with increasing pressure, the decay curves from the 4 F3/2 are nonexponential and faster indicating that the energy transfer processes between Nd3+ ions are important. © 2007 Elsevier B.V. All rights reserved. Keywords: High pressure; Nd3+ ; Laser; Scheelite; Luminescence
1. Introduction
2. Experimental
The scheelite-structured SrWO4 crystals show optimal conditions to obtain optically homogeneous single crystals free of light scattering centers and growth striations [1]. In this way, this matrix doped with different rare earth ions is very interesting for multifunctional lasers [1,2]. In a previous paper the optical properties of SrWO4 crystals doped with Nd3+ ions have been studied as function of temperature (10–300 K) [3]. The Nd3+ ions are incorporated into the crystals in the position of Sr2+ ions, therefore the optical bands of Nd3+ ions are broadened because of crystal field inhomogeneities. This characteristic is very interesting in order to use this matrix doped with Nd3+ ions as a tunable laser. The aim of this work is to analyze the emission bands of Nd3+ ions in the SrWO4 crystal as a function of pressure. Moreover, monitoring these results it is expected to detect the phase transition found in the pure matrix at around 10 GPa [4].
The SrWO4 crystals were prepared by the Czochralski technique as indicated in detail in Ref. [5]. The Nd3+ concentration was 0.33 at.% Nd:SrWO4 measured by the ICP-AES method [5]. The luminescence of the Nd3+ ions was obtained exciting with an Argon laser and detected through a 0.75 m monochromator with a photomultiplier. The temporal evolution measurements were carried out with a pulsed Nd:YAG laser at 532 nm. The pulse duration was 5 ns and the repetition rate was 20 Hz. The time resolved fluorescence was recorded using a digital storage oscilloscope controlled by a personal computer. In order to perform the nearly hydrostatic high-pressure measurements the Nd3+ :SrWO4 crystal was inserted in a diamondanvil cell. Paraffin oil was used as the pressure transmitting medium and the pressure was determined by the ruby fluorescence technique.
∗
Corresponding author. E-mail address: [email protected] (I.R. Mart´ın).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.04.180
3. Results and discussion The emission band corresponding to the 4 F3/2 → 4 I9/2 transition of Nd3+ ions in a SrWO4 crystal as a function of pressure is presented in Fig. 1. At low pressure (0.4 GPa) the emission spectrum is similar to the spectrum obtained at ambient pressure in the same matrix in Ref. [3] or to the spectrum obtained in Nd3+ :YLiF4 with a similar scheelite structure at low pressure in Ref. [6]. Furthermore, when the pressure is increased, this emission shows the typical red shift (see Fig. 1) and thus a
D. Errandonea et al. / Journal of Alloys and Compounds 451 (2008) 212–214
4F 3/2
→ 4 I9/2
Fig. 1. Emission spectra corresponding to the transition obtained in a SrWO4 crystal doped with Nd3+ crystal measured at RT at different pressures. The spectra collected on pressure release are marked with (r). Numbers identify the different emission peaks.
corresponding reduction of the free energy of the ions. At low pressures, the Stark splitting of the 4 F3/2 and 4 I9/2 multiplets give place to about 10 peaks in this emission. The position of these peaks as function of pressure is presented in Fig. 2. As can be seen in this figure, when the pressure increases the peak positions shift or disappear and there is an important change in the emission spectrum about 10 GPa (specially in the peaks located at about 920 nm). All the changes induced by pressure in the emission spectrum are reversible upon decompression (see Fig. 1). In a previous paper, a scheelite to fergusonite phase transition was detected by means of X-ray diffraction measurements around 10.5 GPa in a pure SrWO4 matrix [4]. The compressibility in the scheelite phase is principally due to the compression of the dodecahedral SrO8 units. The fergusonite phase is a distorted and compressed version of scheelite obtained by a distortion of the cation matrix [7]. The structural changes induced by pressure at the scheelite to fergusonite transition are known to affect the electronic properties [8] and the luminescence spectrum [6] of compounds isostructural to SrWO4 . In the present case, as the Nd3+ ions are located in the sites of the Sr3+ ions, the phase transition at about 10 GPa is also very well monitored by the emission of these ions as can be seen in Fig. 2. The dependence of the displacements of the peaks with the pressure changes
213
Fig. 2. Peak positions observed in the 4 F3/2 → 4 I9/2 transition increasing (full circles) and decreasing (open circles) the pressure.
below and above 10 GPa due to the different compressibility of the scheelite and fergusonite phases confirming in this way the previously found phase transition in the pure crystal [4]. Additionally, the luminescence peaks located in the long wavelength part of the spectrum considerable broaden after the phase transition. It is important to note here that for the high-pressure phase, upon pressure release from 13 GPa to 10 GPa, the peaks located near 920 nm displace relatively to its position when pressure increases. This different behaviour can be caused by distortions induced in the local environment of Nd3+ , but can be also an artefact error caused by the fact that upon pressure release the 920 nm peaks remain broadened until the low-pressure phase is recovered. Further research is in progress to clarify this issue. The Nd3+ ions in the crystal are located in the position of the Sr2+ ions, however it is possible that the Nd3+ ions are forming clusters. In order to obtain information about their distribution in the crystal the decay curves of the 4 F3/2 level have been measured as function of pressure. These decays curves are nonexponential due to the energy transfer processes between Nd3+ ions. In this way, the decay curves are relatively well fitted to the Inokuti–Hirayama model [9] or to the generalized Yokota–Tanimoto model [10], indicating that the Nd3+ ions are randomly distributed (not forming clusters) in the crystal. Therefore, it has been defined the effective lifetime of the decay curves
214
D. Errandonea et al. / Journal of Alloys and Compounds 451 (2008) 212–214
4. Conclusions The emission spectra for the 4 F3/2 → 4 I9/2 transition have been obtained under pressure (from ambient condition until 13 GPa) in a Nd3+ :SrWO4 crystal. The changes observed in the emission spectra confirm the scheelite to fergusonite phase transition which is observed in pure crystals around 10 GPa. From the analysis of the luminescence decays as function of pressure from the 4 F3/2 level, it is concluded that the energy transfer processes are important due to the nonexponentiality of these decay curves. These processes are probably the most important factor which explains the reduction of the effective lifetime when the pressure is increased. Acknowledgements Effective lifetimes for the 4 F3/2 level increasing (full circles) and decreas-
Fig. 3. ing (open circles) the pressure.
using the following equation: I(t) dt τ = I(0)
This work has been supported by ‘Comisi´on Interministerial de Ciencia y Tecnolog´ıa’ under projects MAT2004-06868 and MAT2004-09867-C03-01, Universidad de La Laguna (SEGAI), and Generalitat Valenciana (ACOMP06/181).
(1)
where I(t) is the fluorescence intensity (corresponding to the measured 4 F3/2 → 4 I9/2 transition). The values obtained for the effective lifetime decrease when the pressure increases, however changes due to the phase transition are not observed taking into account the dispersion of the data (see Fig. 3). The values for the effective lifetime depend on the intrinsic relaxation of the ions (intrinsic lifetime) and the energy transfer processes between Nd3+ ions. The intrinsic lifetime depends on the pressure because the electronic transition probabilities depend on the crystal-field which acts on the Nd3+ ions. Respect to the energy transfer processes, when the pressure increases also the effective concentration of Nd3+ ions in the crystal increases and the energy transfer processes are more efficient. Therefore, due to these processes it is expected a reduction in the effective lifetime as it is observed in other works [11]. However, it is interesting to obtain independently the dependence of the intrinsic lifetime and the energy transfer probability as function of the pressure from the decay curves. This study is possible comparing the decay curves of samples with different Nd3+ concentration using a generalized Yokota-Tanimoto model [10] in similar way to Ref. [11].
References [1] L.I. Ivleva, T.T. Basiev, I.S. Voronina, P.G. Zverev, V.V. Osiko, N.M. Polozkov, Opt. Mater. 23 (2003) 439. [2] G. Jia, C. Tu, A. Brenier, Z. You, J. Li, Z. Zhu, Y. Wang, B. Wu, Appl. Phys. B 81 (2005) 627. [3] F. Cornacchia, A. Toncelli, M. Tonelli, E. Cavalli, E. Bovero, N. Magnani, J. Phys. Cond. Matter 16 (2004) 6867. [4] D. Errandonea, J. Pellicer-Porres, F.J. Manj´on, A. Segura, Ch. Ferrer-Roca, R.S. Kumar, O. Tschauner, P. Rodr´ıguez-Hern´andez, J. L´opez-Solano, S. Radescu, A. Mujica, A. Mu˜noz, G. Aquilanti, Phys. Rev. B 72 (2005) 174106. [5] G. Jia, C. Tu, Z. You, J. Li, Z. Zhu, Y. Wang, B. Wu, J. Cryst. Growth 273 (2004) 220. [6] F.J. Manj´on, D. Jandl, K. Syassen, J.Y. Gesland, Phys. Rev. B 64 (2001) 235108. [7] D. Errandonea, Europhys. Lett. 77 (2007) 56001. [8] D. Errandonea, D. Mart´ınez-Garc´ıa, R. Lacomba-Perales, J. Ruiz-Fuertes, A. Segura, Appl. Phys. Lett. 89 (2006) 091913. [9] M. Inokuti, F. Hirayama, J. Chem. Phys. 43 (1965) 1978. [10] I.R. Mart´ın, V.D. Rodr´ıguez, U.R. Rodr´ıguez-Mendoza, V. Lav´ın, E. Montoya, D. Jaque, J. Chem. Phys. 111 (1999) 1191. [11] V. Lav´ın, I.R. Mart´ın, C.K. Jayasankar, Th. Troster, Phys. Rev. B 66 (2002) 64207.
Effect of pressure on the luminescence properties of Nd3+ doped SrWO4 laser crystal D. Errandonea a , Chaoyang Tu b,c , Guohua Jia b,c , I.R. Mart´ın d,∗ , U.R. Rodr´ıguez-Mendoza d , F. Lahoz d , M.E. Torres e , V. Lav´ın d a
Dpto. F´ısica Aplicada-ICMUV, Universitat de Val`encia, Edificio de Investigaci´on, c/Dr. Moliner 50, 46100 Burjassot, Valencia, Spain b Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China c Graduated School of Chinese Academy of Science, 100039 Beijing, China d Dpto. F´ısica Fundamental y Experimental, Electr´ onica y Sistemas, Univ. de La Laguna, Avda. Astrof. Fco. S´anchez, s/n La Laguna 38206, Spain e Dpto. F´ısica B´ asica, Univ. de La Laguna, Avda. Astrof. Fco. S´anchez, s/n La Laguna 38206, Spain Available online 18 April 2007
Abstract The luminescence spectra of the 4 F3/2 → 4 I9/2 transition of Nd3+ ions in a SrWO4 crystal have been analyzed as a function of pressure at room temperature. Experiments have been performed in a diamond-anvil cell up to 13 GPa. At around 10 GPa some changes in the emission spectra have been observed which are attributed to a structural phase transition of the SrWO4 matrix. These results are in good agreement with a previous paper, in which in a pure SrWO4 matrix a scheelite to fergusonite phase transition is found around 10.5 GPa. Moreover, with increasing pressure, the decay curves from the 4 F3/2 are nonexponential and faster indicating that the energy transfer processes between Nd3+ ions are important. © 2007 Elsevier B.V. All rights reserved. Keywords: High pressure; Nd3+ ; Laser; Scheelite; Luminescence
1. Introduction
2. Experimental
The scheelite-structured SrWO4 crystals show optimal conditions to obtain optically homogeneous single crystals free of light scattering centers and growth striations [1]. In this way, this matrix doped with different rare earth ions is very interesting for multifunctional lasers [1,2]. In a previous paper the optical properties of SrWO4 crystals doped with Nd3+ ions have been studied as function of temperature (10–300 K) [3]. The Nd3+ ions are incorporated into the crystals in the position of Sr2+ ions, therefore the optical bands of Nd3+ ions are broadened because of crystal field inhomogeneities. This characteristic is very interesting in order to use this matrix doped with Nd3+ ions as a tunable laser. The aim of this work is to analyze the emission bands of Nd3+ ions in the SrWO4 crystal as a function of pressure. Moreover, monitoring these results it is expected to detect the phase transition found in the pure matrix at around 10 GPa [4].
The SrWO4 crystals were prepared by the Czochralski technique as indicated in detail in Ref. [5]. The Nd3+ concentration was 0.33 at.% Nd:SrWO4 measured by the ICP-AES method [5]. The luminescence of the Nd3+ ions was obtained exciting with an Argon laser and detected through a 0.75 m monochromator with a photomultiplier. The temporal evolution measurements were carried out with a pulsed Nd:YAG laser at 532 nm. The pulse duration was 5 ns and the repetition rate was 20 Hz. The time resolved fluorescence was recorded using a digital storage oscilloscope controlled by a personal computer. In order to perform the nearly hydrostatic high-pressure measurements the Nd3+ :SrWO4 crystal was inserted in a diamondanvil cell. Paraffin oil was used as the pressure transmitting medium and the pressure was determined by the ruby fluorescence technique.
∗
Corresponding author. E-mail address: [email protected] (I.R. Mart´ın).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.04.180
3. Results and discussion The emission band corresponding to the 4 F3/2 → 4 I9/2 transition of Nd3+ ions in a SrWO4 crystal as a function of pressure is presented in Fig. 1. At low pressure (0.4 GPa) the emission spectrum is similar to the spectrum obtained at ambient pressure in the same matrix in Ref. [3] or to the spectrum obtained in Nd3+ :YLiF4 with a similar scheelite structure at low pressure in Ref. [6]. Furthermore, when the pressure is increased, this emission shows the typical red shift (see Fig. 1) and thus a
D. Errandonea et al. / Journal of Alloys and Compounds 451 (2008) 212–214
4F 3/2
→ 4 I9/2
Fig. 1. Emission spectra corresponding to the transition obtained in a SrWO4 crystal doped with Nd3+ crystal measured at RT at different pressures. The spectra collected on pressure release are marked with (r). Numbers identify the different emission peaks.
corresponding reduction of the free energy of the ions. At low pressures, the Stark splitting of the 4 F3/2 and 4 I9/2 multiplets give place to about 10 peaks in this emission. The position of these peaks as function of pressure is presented in Fig. 2. As can be seen in this figure, when the pressure increases the peak positions shift or disappear and there is an important change in the emission spectrum about 10 GPa (specially in the peaks located at about 920 nm). All the changes induced by pressure in the emission spectrum are reversible upon decompression (see Fig. 1). In a previous paper, a scheelite to fergusonite phase transition was detected by means of X-ray diffraction measurements around 10.5 GPa in a pure SrWO4 matrix [4]. The compressibility in the scheelite phase is principally due to the compression of the dodecahedral SrO8 units. The fergusonite phase is a distorted and compressed version of scheelite obtained by a distortion of the cation matrix [7]. The structural changes induced by pressure at the scheelite to fergusonite transition are known to affect the electronic properties [8] and the luminescence spectrum [6] of compounds isostructural to SrWO4 . In the present case, as the Nd3+ ions are located in the sites of the Sr3+ ions, the phase transition at about 10 GPa is also very well monitored by the emission of these ions as can be seen in Fig. 2. The dependence of the displacements of the peaks with the pressure changes
213
Fig. 2. Peak positions observed in the 4 F3/2 → 4 I9/2 transition increasing (full circles) and decreasing (open circles) the pressure.
below and above 10 GPa due to the different compressibility of the scheelite and fergusonite phases confirming in this way the previously found phase transition in the pure crystal [4]. Additionally, the luminescence peaks located in the long wavelength part of the spectrum considerable broaden after the phase transition. It is important to note here that for the high-pressure phase, upon pressure release from 13 GPa to 10 GPa, the peaks located near 920 nm displace relatively to its position when pressure increases. This different behaviour can be caused by distortions induced in the local environment of Nd3+ , but can be also an artefact error caused by the fact that upon pressure release the 920 nm peaks remain broadened until the low-pressure phase is recovered. Further research is in progress to clarify this issue. The Nd3+ ions in the crystal are located in the position of the Sr2+ ions, however it is possible that the Nd3+ ions are forming clusters. In order to obtain information about their distribution in the crystal the decay curves of the 4 F3/2 level have been measured as function of pressure. These decays curves are nonexponential due to the energy transfer processes between Nd3+ ions. In this way, the decay curves are relatively well fitted to the Inokuti–Hirayama model [9] or to the generalized Yokota–Tanimoto model [10], indicating that the Nd3+ ions are randomly distributed (not forming clusters) in the crystal. Therefore, it has been defined the effective lifetime of the decay curves
214
D. Errandonea et al. / Journal of Alloys and Compounds 451 (2008) 212–214
4. Conclusions The emission spectra for the 4 F3/2 → 4 I9/2 transition have been obtained under pressure (from ambient condition until 13 GPa) in a Nd3+ :SrWO4 crystal. The changes observed in the emission spectra confirm the scheelite to fergusonite phase transition which is observed in pure crystals around 10 GPa. From the analysis of the luminescence decays as function of pressure from the 4 F3/2 level, it is concluded that the energy transfer processes are important due to the nonexponentiality of these decay curves. These processes are probably the most important factor which explains the reduction of the effective lifetime when the pressure is increased. Acknowledgements Effective lifetimes for the 4 F3/2 level increasing (full circles) and decreas-
Fig. 3. ing (open circles) the pressure.
using the following equation: I(t) dt τ = I(0)
This work has been supported by ‘Comisi´on Interministerial de Ciencia y Tecnolog´ıa’ under projects MAT2004-06868 and MAT2004-09867-C03-01, Universidad de La Laguna (SEGAI), and Generalitat Valenciana (ACOMP06/181).
(1)
where I(t) is the fluorescence intensity (corresponding to the measured 4 F3/2 → 4 I9/2 transition). The values obtained for the effective lifetime decrease when the pressure increases, however changes due to the phase transition are not observed taking into account the dispersion of the data (see Fig. 3). The values for the effective lifetime depend on the intrinsic relaxation of the ions (intrinsic lifetime) and the energy transfer processes between Nd3+ ions. The intrinsic lifetime depends on the pressure because the electronic transition probabilities depend on the crystal-field which acts on the Nd3+ ions. Respect to the energy transfer processes, when the pressure increases also the effective concentration of Nd3+ ions in the crystal increases and the energy transfer processes are more efficient. Therefore, due to these processes it is expected a reduction in the effective lifetime as it is observed in other works [11]. However, it is interesting to obtain independently the dependence of the intrinsic lifetime and the energy transfer probability as function of the pressure from the decay curves. This study is possible comparing the decay curves of samples with different Nd3+ concentration using a generalized Yokota-Tanimoto model [10] in similar way to Ref. [11].
References [1] L.I. Ivleva, T.T. Basiev, I.S. Voronina, P.G. Zverev, V.V. Osiko, N.M. Polozkov, Opt. Mater. 23 (2003) 439. [2] G. Jia, C. Tu, A. Brenier, Z. You, J. Li, Z. Zhu, Y. Wang, B. Wu, Appl. Phys. B 81 (2005) 627. [3] F. Cornacchia, A. Toncelli, M. Tonelli, E. Cavalli, E. Bovero, N. Magnani, J. Phys. Cond. Matter 16 (2004) 6867. [4] D. Errandonea, J. Pellicer-Porres, F.J. Manj´on, A. Segura, Ch. Ferrer-Roca, R.S. Kumar, O. Tschauner, P. Rodr´ıguez-Hern´andez, J. L´opez-Solano, S. Radescu, A. Mujica, A. Mu˜noz, G. Aquilanti, Phys. Rev. B 72 (2005) 174106. [5] G. Jia, C. Tu, Z. You, J. Li, Z. Zhu, Y. Wang, B. Wu, J. Cryst. Growth 273 (2004) 220. [6] F.J. Manj´on, D. Jandl, K. Syassen, J.Y. Gesland, Phys. Rev. B 64 (2001) 235108. [7] D. Errandonea, Europhys. Lett. 77 (2007) 56001. [8] D. Errandonea, D. Mart´ınez-Garc´ıa, R. Lacomba-Perales, J. Ruiz-Fuertes, A. Segura, Appl. Phys. Lett. 89 (2006) 091913. [9] M. Inokuti, F. Hirayama, J. Chem. Phys. 43 (1965) 1978. [10] I.R. Mart´ın, V.D. Rodr´ıguez, U.R. Rodr´ıguez-Mendoza, V. Lav´ın, E. Montoya, D. Jaque, J. Chem. Phys. 111 (1999) 1191. [11] V. Lav´ın, I.R. Mart´ın, C.K. Jayasankar, Th. Troster, Phys. Rev. B 66 (2002) 64207.