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Fluorescence and persistent spectral hole burning of Eu3+ in Ge–Ga–S–KBr glasses
Journal of Luminescence 99 (2002) 73–77
Fluorescence and persistent spectral hole burning of Eu3+ in Ge–Ga–S–KBr glasses Woon Jin Chung*, Jong Heo Photonic Glasses Laboratory, Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-dong, Nam-gu, Pohang, Kyungbuk, 790-784, South Korea Received 8 February 2001; received in revised form 18 June 2001; accepted 13 July 2001
Abstract Fluorescence and efficient persistent spectral hole burning of Eu3+ at 77 K were observed in chalcohalide glasses. The depth of the hole was approximately 30% after a burning process of 1 min with 50 mW power, and it was completely erased with Ar+ laser irradiation. The hole survived room temperature heat treatment and showed good thermal stability. The hole-burning mechanism was most probably the photo-reduction of Eu3+-Eu2+. Fluorescence from Eu3+ decreased with increasing temperature and disappeared at the temperature above B130 K. r 2002 Elsevier Science B.V. All rights reserved. PACS: 32.70.n; 32.70.Jz; 42.70.Ce; 78.55.Hx Keywords: Eu3+; Fluorescence; Hole burning; Chalcohalide; Glass
1. Introduction Persistent spectral hole burning (PSHB) in rareearth doped materials has potential applications to high-density optical memory devices [1,2]. Among many host materials for rare-earths, glasses provide advantages of a large inhomogeneous linewidth and high transmittance in the optical spectrum. Oxide glasses were mainly used as hosts and in fact, PSHB was realized at temperatures above 77 K from the borate and silicate glasses doped with Sm2+ or Eu3+ [3–7]. On the other
*Corresponding author. Tel.: +82-54279-2821; fax: +8254279-5872. E-mail address: [email protected] (W.J. Chung).
hand, sulfide glasses can provide a long excitedstate lifetime and high quantum efficiency of the emission compared to oxides, largely due to the low fundamental vibrational energy of the chemical bonds in sulfides [8]. Therefore, there is less probability of losing the excited-state energy to the phonon vibration of the hosts. However, there have been no reports on the high-temperature (>77 K) PSHB phenomenon in sulfide hosts except for low-temperature (o10 K) observation from CaS and MgS crystals [9,10] doped with Eu2+. This report concerns the fluorescence and spectral hole burning from Eu3+ in sulfide glasses modified with alkali-halide. The formation of the holes in Eu3+ was observed at the temperature of 77 K, and the holes were stable against the thermal annealing at room temperature.
0022-2313/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 2 3 1 3 ( 0 1 ) 0 0 2 3 3 - 2
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W.J. Chung, J. Heo / Journal of Luminescence 99 (2002) 73–77
2. Experimental procedures Composition of the host glass was 15.25Ge+15.25Ga+54.25S+15.25KBr (mol%) doped with 0.1 mol% of Eu ions. KBr was added to enhance the thermal stability and visible transmittance of the glass. Approximately 8 g of high-purity starting materials (>99.99% Ge, Ga, S, KBr, and Eu) were batched into the silica tube inside a dry glove box filled with high-purity argon gas. The silica tube was removed from the dry box and sealed to avoid the contamination of oxygen and moisture. Melting was done at 9501C for 10 h using a rocking furnace. After melting, the silica tube containing the melt was removed from the furnace and quenched into water. Then, it was annealed at 3101C for 1 h and slowly cooled down to room temperature. The specimen was removed from the tube and optically polished for the spectroscopic measurements. A rhodamine 6G Dye laser (Coherentt 899-01) pumped by an Ar+ laser was used for the excitation source. Linewidth of the laser beam was less than 0.7 cm1. The sample was placed in a cryostat system (Oxford CCC1104) cooled by compressed helium gas. Fluorescence was recorded by a photo-multiplier tube combined with a monochromator, lock-in amplifier and oscilloscope. Excitation spectra were measured by monitoring fluorescence intensity change of the Eu3+ : 5D0-7F2 transition. The laser intensity was attenuated by a factor of 20 using a neutral density filter to avoid possible contamination on hole spectrum during the measurement.
3. Results The fluorescence spectrum shown in Fig. 1 was recorded at 10 K with an excitation beam of 579.7 nm in wavelength. It showed characteristic emissions due to the transitions from the Eu3+ : 5D0 level to lower-lying energy levels [11]. Emissions from Eu3+ have not been observed in sulfide glasses without KBr, but were observed at the temperature below B130 K with KBr addition. The excitation spectrum of 7F0-5D0 in Fig. 2(a) showed an inhomogeneous linewidth
Fig. 1. Fluorescence spectrum of the Eu3+-doped Ge–Ga–S– KBr glass recorded at 10 K. Wavelength of the pump source was 579.7 nm.
Fig. 2. (a) Excitation spectrum of Eu3+ : 5D0 in Ge–Ga–S–KBr glass and (b) hole-burning spectrum after irradiation with the 579.7 nm laser beam for 1 min at 77 K. Top figure shows the difference between the two spectra.
with a full-width at the half-maximum (FWHM) intensity of B13 cm1. It is narrower compared to those in other oxide glasses (B30 cm1) [4–7]. It implies that the site-to-site variation of Eu3+ in Ge–Ga–S–KBr glass is less compared to other hosts. Hole burning was performed at 77 K on the excitation spectrum of the 7F0-5D0 transition by irradiating the 579.7 nm laser beam with B50 mW power for 1 min on a sample (Fig. 2(b)). The depth of the hole was approximately 30% of the total fluorescence intensity and it is considerably larger than those reported from oxide glass hosts [3–7]. Furthermore, it was possible to detect the hole without any significant changes in its profile even
W.J. Chung, J. Heo / Journal of Luminescence 99 (2002) 73–77
Fig. 3. Excitation spectra of Eu3+ recorded: (a) after the hole burning at 579.7 nm for 1 min; (b) after annealing at 150 K; (c) after annealing at 293 K for 1 min, and (d) before the hole burning. Inner graph represents the corresponding intensity changes at each temperature. All spectra were recorded at 77 K.
after 3 h at 77 K, and the hole was considered to be persistent. A single Lorentzian fitting to the hole profile showed a hole width of B2.1 cm1 in FWHM, which is comparable to those obtained from oxide glass hosts (3–4 cm1) [4–7]. In order to examine the thermal stability of the hole, the excitation spectrum was recorded at 77 K after annealing the hole at 150 K and room temperature for 1 min. As shown in Fig. 3, the hole clearly survived the thermal treatment of the 150 K annealing and, to some extent, an annealing at room temperature. The result suggested the good thermal stability of the holes in these glasses.
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the hole-burning process. In order to examine the mechanism of hole burning in this system, the hole was burnt at 579.75 nm for 5 min and then, Ar+ laser beam (l ¼ 514 nm) corresponding to the Eu2+ : 4f7-4f65d1 transition was irradiated on the sample for 10 min at 77 K. The hole was completely erased as shown in Fig. 4. This hole erasure is due to the ionization of Eu2+, which was formed during the hole-burning process, to Eu3+. Moreover, there is no anti-hole in the spectrum of Fig. 2. During the photo-reduction of Eu3+, Eu2+ plays an important role by capturing the released hole. The presence of Eu2+ in the Ge–Ga–S–KBr glass was clearly observed from electron spin resonance (ESR) spectra as shown in Fig. 5. It showed broad ESR signals at g value of 2–6 which is a characteristic ESR signal of Eu2+ in glasses [12,13]. The latter mechanism of OH rearrangement around Eu3+ could also be considered important at temperatures below B150 K [6,7]. However, this mechanism is not appropriate for the present glass system since the glasses were prepared in an inert atmosphere to minimize the contamination from the oxygen and humidity. Therefore, the former mechanism of the photoreduction appears to be adequate for our system. The efficient and complete erasure of the hole with the second light provides an opportunity towards the read-and-write optical storage applications.
4. Discussion Two mechanisms have been proposed to explain the hole-burning phenomena in Eu3+ at temperatures above 77 K. First, Fujita et al. [4,5] suggested the photo-induced reduction of Eu3+ to Eu2+ through a one-photon process. They proposed this mechanism from the observation of a partial hole-filling with Ar+ laser irradiation and also from the absence of anti-hole on the hole-burning spectrum. In this process, Eu2+ originally present in glasses became a hole-trapping center. On the other hand, Nogami et al. [6,7] proposed the optically activated rearrangement of the OH bonds around Eu3+ ions as a major source of
Fig. 4. Effect of argon laser (l ¼ 514 nm) irradiation on the excitation spectra of Eu3+ : 5D0. (a) Excitation spectra before and after the hole burning at 579.75 nm for 5 min. (b) After Ar+ laser irradiation for 10 min. All experiments were performed at 77 K.
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Fig. 5. ESR spectrum of 0.1 mol% Eu3+-doped Ge–Ga–S– KBr glass at 77 K.
Emission spectra and hole profiles in Figs. 1 and 2 changed significantly as the temperatures of measurement increased from 20 to 150 K. First, the hole decreased in depth and became broad as the temperature increased (Fig. 6). This change in hole profile with temperature was similar to that found from other host glasses [3–7]. At the same time, however, the fluorescence from Eu3+ also decreased in intensity and it became difficult to find any emissions from Eu3+ at temperatures above B130 K as well as the excitation spectrum. In order to investigate the temperature dependence of the fluorescence, intensity of the Eu3+ : 5D0-7F2 transition was monitored at various temperatures. Fig. 7 shows that the fluorescence from Eu3+ disappeared at temperatures above B130 K. A large increase in the phonon vibration of the host glass at high temperatures might be responsible for the decrease in the fluorescence intensities [14]. However, the energy separation between the fluorescing level (5D0) and the next lower-lying energy level in Eu3+ is approximately 12,000 cm1. Since the local fundamental vibration energy around the rareearth ion is only B245 cm1 in chalcohalide glasses [15], it is difficult to believe that the quenching of the fluorescences is due to the multiphonon relaxation only. There may be another mechanism responsible for the decrease in the electron population of the 5D0 level. There have been several reports on change of the oxidation states, i.e. Eu3+-Eu2+ in metallic compounds
Fig. 6. Excitation spectra of Eu3+ : 5D0 and hole profiles varying temperature from 20 to 77 and 110 K. Hole was burnt and observed at each temperature.
Fig. 7. Emission intensity change of Eu3+ : 5D0-7F2 with temperature of Ge–Ga–S–KBr glass. Excitation wavelength was 579.7 nm.
with increasing temperature [16,17]. It is due to the electron fluctuation between the localized 4f level and conduction band in Eu3+. The change in the oxidation states of europium ions provides an answer for the disappearance of Eu3+ fluorescence with temperature. However, further works are necessary to understand the origin of the large decrease in the Eu3+ fluorescence at high temperatures. The depth of the hole in chalcohalide glass (B30% with 1 min burning) was significantly deeper than those of Eu3+ in oxides [4–7], which
W.J. Chung, J. Heo / Journal of Luminescence 99 (2002) 73–77
is about 10% with >5 min burning at 77 K. Furthermore, it was possible to erase the hole completely with the second light source (B488 or 514 nm), while the holes in oxide glasses were only partly filled. The reasons for this enhancement in the hole characteristics are probably due to either the high quantum efficiency of Eu3+ ion or the effectiveness of the photo-reduction process in the chalcohalide host. In any case, the effectiveness in burning and erasing a hole in chalcohalide glasses provides a vital condition for the high-density optical storage such as holographic memory. Although the narrow inhomogeneous linewidth may reduce the memory capacity both in frequency or time-domain memory system [1,2], it is useful as a medium for the volume holographic memory. One should mention that fluorescence properties of Eu3+, or rare-earths in general, showed strong dependence on composition and temperature and the dependence is, in turn, closely related to the chemical and structural properties of the host matrix. Hole-burning properties of the present system should also be related to the chemical nature of the host glasses. A detailed study on the nature and mechanism of the hole burning in this new glass needs to be carried out.
5. Conclusion In conclusion, we observed the fluorescence and PSHB from the Eu3+-doped chalcohalide glass at 77 K. The hole depth was 30% at 77 K and was completely erased with Ar+ laser (l ¼ 488 or 514 nm) irradiation. The hole survived the thermal
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annealing at room temperature. However, the fluorescence from Eu3+ was quenched when the temperature of measurement was above B130 K. Photo-induced reduction of Eu3+-Eu2+ is the most probable hole-burning mechanism.
References [1] W.E. Moerner, Persistent Spectral Hole-Burning: Science and Applications, Springer, Berlin, 1988. [2] T.W. Mossberg, Opt. Lett. 7 (1982) 77. [3] D.H. Cho, K. Hirao, N. Soga, J. Non-Cryst. Solids 189 (1995) 181. [4] K. Fujita, K. Tanaka, K. Hirao, N. Soga, J. Opt. Am. B 15 (1998) 2700. [5] K. Fujita, K. Tanaka, K. Hirao, N. Soga, Opt. Lett. 23 (1998) 543. [6] M. Nogami, T. Hayakawa, Phys. Rev. B 56 (1997) R14235. [7] M. Nogami, T. Nagakura, T. Hayakawa, J. Phys.: Condens. Matter 11 (1999) 335. [8] K. Wei, D.P. Machewirth, J. Wenzel, E. Snitzer, G.H. Sigel Jr., J. Non-Cryst. Solids 182 (1995) 257. [9] Z. Hasan, M. Solonenko, P.I. Macfarlane, L. Biyikli, V.K. Mathur, F.A. Karwacki, Appl. Phys. Lett. 72 (1998) 2373. [10] Z. Hasan, L. Biylikli, P.I. Macfarlane, Appl. Phys. Lett. 72 (1998) 3399. [11] R. Reisfeld, E. Greenberg, R.N. Brown, M.G. Drexhage, C.K. Jorgensen, Chem. Phys. Lett. 95 (1983) 91. [12] R.C. Nicklin, J.K. Johnstone, R.G. Barnes, D.R. Wilder, J. Chem. Phys. 59 (1973) 1652. [13] T. Hayakawa, M. Nogami, Solid State Commun. 116 (2000) 77. [14] Miyakawa, D.L. Dexter, Phys. Rev. B 1 (1970) 2961. [15] Y.B. Shin, J. Heo, H.S. Kim, Chem. Phys. Lett. 317 (2000) 637. [16] E.R. Bauminger, D. Froindlich, I. Nowik, S. Ofer, I. Felner, I. Mayer, Phys. Rev. Lett. 30 (1973) 1053. [17] I. Felner, I. Nowik, Physica B 182 (1992) 145.
Fluorescence and persistent spectral hole burning of Eu3+ in Ge–Ga–S–KBr glasses Woon Jin Chung*, Jong Heo Photonic Glasses Laboratory, Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-dong, Nam-gu, Pohang, Kyungbuk, 790-784, South Korea Received 8 February 2001; received in revised form 18 June 2001; accepted 13 July 2001
Abstract Fluorescence and efficient persistent spectral hole burning of Eu3+ at 77 K were observed in chalcohalide glasses. The depth of the hole was approximately 30% after a burning process of 1 min with 50 mW power, and it was completely erased with Ar+ laser irradiation. The hole survived room temperature heat treatment and showed good thermal stability. The hole-burning mechanism was most probably the photo-reduction of Eu3+-Eu2+. Fluorescence from Eu3+ decreased with increasing temperature and disappeared at the temperature above B130 K. r 2002 Elsevier Science B.V. All rights reserved. PACS: 32.70.n; 32.70.Jz; 42.70.Ce; 78.55.Hx Keywords: Eu3+; Fluorescence; Hole burning; Chalcohalide; Glass
1. Introduction Persistent spectral hole burning (PSHB) in rareearth doped materials has potential applications to high-density optical memory devices [1,2]. Among many host materials for rare-earths, glasses provide advantages of a large inhomogeneous linewidth and high transmittance in the optical spectrum. Oxide glasses were mainly used as hosts and in fact, PSHB was realized at temperatures above 77 K from the borate and silicate glasses doped with Sm2+ or Eu3+ [3–7]. On the other
*Corresponding author. Tel.: +82-54279-2821; fax: +8254279-5872. E-mail address: [email protected] (W.J. Chung).
hand, sulfide glasses can provide a long excitedstate lifetime and high quantum efficiency of the emission compared to oxides, largely due to the low fundamental vibrational energy of the chemical bonds in sulfides [8]. Therefore, there is less probability of losing the excited-state energy to the phonon vibration of the hosts. However, there have been no reports on the high-temperature (>77 K) PSHB phenomenon in sulfide hosts except for low-temperature (o10 K) observation from CaS and MgS crystals [9,10] doped with Eu2+. This report concerns the fluorescence and spectral hole burning from Eu3+ in sulfide glasses modified with alkali-halide. The formation of the holes in Eu3+ was observed at the temperature of 77 K, and the holes were stable against the thermal annealing at room temperature.
0022-2313/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 2 3 1 3 ( 0 1 ) 0 0 2 3 3 - 2
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W.J. Chung, J. Heo / Journal of Luminescence 99 (2002) 73–77
2. Experimental procedures Composition of the host glass was 15.25Ge+15.25Ga+54.25S+15.25KBr (mol%) doped with 0.1 mol% of Eu ions. KBr was added to enhance the thermal stability and visible transmittance of the glass. Approximately 8 g of high-purity starting materials (>99.99% Ge, Ga, S, KBr, and Eu) were batched into the silica tube inside a dry glove box filled with high-purity argon gas. The silica tube was removed from the dry box and sealed to avoid the contamination of oxygen and moisture. Melting was done at 9501C for 10 h using a rocking furnace. After melting, the silica tube containing the melt was removed from the furnace and quenched into water. Then, it was annealed at 3101C for 1 h and slowly cooled down to room temperature. The specimen was removed from the tube and optically polished for the spectroscopic measurements. A rhodamine 6G Dye laser (Coherentt 899-01) pumped by an Ar+ laser was used for the excitation source. Linewidth of the laser beam was less than 0.7 cm1. The sample was placed in a cryostat system (Oxford CCC1104) cooled by compressed helium gas. Fluorescence was recorded by a photo-multiplier tube combined with a monochromator, lock-in amplifier and oscilloscope. Excitation spectra were measured by monitoring fluorescence intensity change of the Eu3+ : 5D0-7F2 transition. The laser intensity was attenuated by a factor of 20 using a neutral density filter to avoid possible contamination on hole spectrum during the measurement.
3. Results The fluorescence spectrum shown in Fig. 1 was recorded at 10 K with an excitation beam of 579.7 nm in wavelength. It showed characteristic emissions due to the transitions from the Eu3+ : 5D0 level to lower-lying energy levels [11]. Emissions from Eu3+ have not been observed in sulfide glasses without KBr, but were observed at the temperature below B130 K with KBr addition. The excitation spectrum of 7F0-5D0 in Fig. 2(a) showed an inhomogeneous linewidth
Fig. 1. Fluorescence spectrum of the Eu3+-doped Ge–Ga–S– KBr glass recorded at 10 K. Wavelength of the pump source was 579.7 nm.
Fig. 2. (a) Excitation spectrum of Eu3+ : 5D0 in Ge–Ga–S–KBr glass and (b) hole-burning spectrum after irradiation with the 579.7 nm laser beam for 1 min at 77 K. Top figure shows the difference between the two spectra.
with a full-width at the half-maximum (FWHM) intensity of B13 cm1. It is narrower compared to those in other oxide glasses (B30 cm1) [4–7]. It implies that the site-to-site variation of Eu3+ in Ge–Ga–S–KBr glass is less compared to other hosts. Hole burning was performed at 77 K on the excitation spectrum of the 7F0-5D0 transition by irradiating the 579.7 nm laser beam with B50 mW power for 1 min on a sample (Fig. 2(b)). The depth of the hole was approximately 30% of the total fluorescence intensity and it is considerably larger than those reported from oxide glass hosts [3–7]. Furthermore, it was possible to detect the hole without any significant changes in its profile even
W.J. Chung, J. Heo / Journal of Luminescence 99 (2002) 73–77
Fig. 3. Excitation spectra of Eu3+ recorded: (a) after the hole burning at 579.7 nm for 1 min; (b) after annealing at 150 K; (c) after annealing at 293 K for 1 min, and (d) before the hole burning. Inner graph represents the corresponding intensity changes at each temperature. All spectra were recorded at 77 K.
after 3 h at 77 K, and the hole was considered to be persistent. A single Lorentzian fitting to the hole profile showed a hole width of B2.1 cm1 in FWHM, which is comparable to those obtained from oxide glass hosts (3–4 cm1) [4–7]. In order to examine the thermal stability of the hole, the excitation spectrum was recorded at 77 K after annealing the hole at 150 K and room temperature for 1 min. As shown in Fig. 3, the hole clearly survived the thermal treatment of the 150 K annealing and, to some extent, an annealing at room temperature. The result suggested the good thermal stability of the holes in these glasses.
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the hole-burning process. In order to examine the mechanism of hole burning in this system, the hole was burnt at 579.75 nm for 5 min and then, Ar+ laser beam (l ¼ 514 nm) corresponding to the Eu2+ : 4f7-4f65d1 transition was irradiated on the sample for 10 min at 77 K. The hole was completely erased as shown in Fig. 4. This hole erasure is due to the ionization of Eu2+, which was formed during the hole-burning process, to Eu3+. Moreover, there is no anti-hole in the spectrum of Fig. 2. During the photo-reduction of Eu3+, Eu2+ plays an important role by capturing the released hole. The presence of Eu2+ in the Ge–Ga–S–KBr glass was clearly observed from electron spin resonance (ESR) spectra as shown in Fig. 5. It showed broad ESR signals at g value of 2–6 which is a characteristic ESR signal of Eu2+ in glasses [12,13]. The latter mechanism of OH rearrangement around Eu3+ could also be considered important at temperatures below B150 K [6,7]. However, this mechanism is not appropriate for the present glass system since the glasses were prepared in an inert atmosphere to minimize the contamination from the oxygen and humidity. Therefore, the former mechanism of the photoreduction appears to be adequate for our system. The efficient and complete erasure of the hole with the second light provides an opportunity towards the read-and-write optical storage applications.
4. Discussion Two mechanisms have been proposed to explain the hole-burning phenomena in Eu3+ at temperatures above 77 K. First, Fujita et al. [4,5] suggested the photo-induced reduction of Eu3+ to Eu2+ through a one-photon process. They proposed this mechanism from the observation of a partial hole-filling with Ar+ laser irradiation and also from the absence of anti-hole on the hole-burning spectrum. In this process, Eu2+ originally present in glasses became a hole-trapping center. On the other hand, Nogami et al. [6,7] proposed the optically activated rearrangement of the OH bonds around Eu3+ ions as a major source of
Fig. 4. Effect of argon laser (l ¼ 514 nm) irradiation on the excitation spectra of Eu3+ : 5D0. (a) Excitation spectra before and after the hole burning at 579.75 nm for 5 min. (b) After Ar+ laser irradiation for 10 min. All experiments were performed at 77 K.
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Fig. 5. ESR spectrum of 0.1 mol% Eu3+-doped Ge–Ga–S– KBr glass at 77 K.
Emission spectra and hole profiles in Figs. 1 and 2 changed significantly as the temperatures of measurement increased from 20 to 150 K. First, the hole decreased in depth and became broad as the temperature increased (Fig. 6). This change in hole profile with temperature was similar to that found from other host glasses [3–7]. At the same time, however, the fluorescence from Eu3+ also decreased in intensity and it became difficult to find any emissions from Eu3+ at temperatures above B130 K as well as the excitation spectrum. In order to investigate the temperature dependence of the fluorescence, intensity of the Eu3+ : 5D0-7F2 transition was monitored at various temperatures. Fig. 7 shows that the fluorescence from Eu3+ disappeared at temperatures above B130 K. A large increase in the phonon vibration of the host glass at high temperatures might be responsible for the decrease in the fluorescence intensities [14]. However, the energy separation between the fluorescing level (5D0) and the next lower-lying energy level in Eu3+ is approximately 12,000 cm1. Since the local fundamental vibration energy around the rareearth ion is only B245 cm1 in chalcohalide glasses [15], it is difficult to believe that the quenching of the fluorescences is due to the multiphonon relaxation only. There may be another mechanism responsible for the decrease in the electron population of the 5D0 level. There have been several reports on change of the oxidation states, i.e. Eu3+-Eu2+ in metallic compounds
Fig. 6. Excitation spectra of Eu3+ : 5D0 and hole profiles varying temperature from 20 to 77 and 110 K. Hole was burnt and observed at each temperature.
Fig. 7. Emission intensity change of Eu3+ : 5D0-7F2 with temperature of Ge–Ga–S–KBr glass. Excitation wavelength was 579.7 nm.
with increasing temperature [16,17]. It is due to the electron fluctuation between the localized 4f level and conduction band in Eu3+. The change in the oxidation states of europium ions provides an answer for the disappearance of Eu3+ fluorescence with temperature. However, further works are necessary to understand the origin of the large decrease in the Eu3+ fluorescence at high temperatures. The depth of the hole in chalcohalide glass (B30% with 1 min burning) was significantly deeper than those of Eu3+ in oxides [4–7], which
W.J. Chung, J. Heo / Journal of Luminescence 99 (2002) 73–77
is about 10% with >5 min burning at 77 K. Furthermore, it was possible to erase the hole completely with the second light source (B488 or 514 nm), while the holes in oxide glasses were only partly filled. The reasons for this enhancement in the hole characteristics are probably due to either the high quantum efficiency of Eu3+ ion or the effectiveness of the photo-reduction process in the chalcohalide host. In any case, the effectiveness in burning and erasing a hole in chalcohalide glasses provides a vital condition for the high-density optical storage such as holographic memory. Although the narrow inhomogeneous linewidth may reduce the memory capacity both in frequency or time-domain memory system [1,2], it is useful as a medium for the volume holographic memory. One should mention that fluorescence properties of Eu3+, or rare-earths in general, showed strong dependence on composition and temperature and the dependence is, in turn, closely related to the chemical and structural properties of the host matrix. Hole-burning properties of the present system should also be related to the chemical nature of the host glasses. A detailed study on the nature and mechanism of the hole burning in this new glass needs to be carried out.
5. Conclusion In conclusion, we observed the fluorescence and PSHB from the Eu3+-doped chalcohalide glass at 77 K. The hole depth was 30% at 77 K and was completely erased with Ar+ laser (l ¼ 488 or 514 nm) irradiation. The hole survived the thermal
77
annealing at room temperature. However, the fluorescence from Eu3+ was quenched when the temperature of measurement was above B130 K. Photo-induced reduction of Eu3+-Eu2+ is the most probable hole-burning mechanism.
References [1] W.E. Moerner, Persistent Spectral Hole-Burning: Science and Applications, Springer, Berlin, 1988. [2] T.W. Mossberg, Opt. Lett. 7 (1982) 77. [3] D.H. Cho, K. Hirao, N. Soga, J. Non-Cryst. Solids 189 (1995) 181. [4] K. Fujita, K. Tanaka, K. Hirao, N. Soga, J. Opt. Am. B 15 (1998) 2700. [5] K. Fujita, K. Tanaka, K. Hirao, N. Soga, Opt. Lett. 23 (1998) 543. [6] M. Nogami, T. Hayakawa, Phys. Rev. B 56 (1997) R14235. [7] M. Nogami, T. Nagakura, T. Hayakawa, J. Phys.: Condens. Matter 11 (1999) 335. [8] K. Wei, D.P. Machewirth, J. Wenzel, E. Snitzer, G.H. Sigel Jr., J. Non-Cryst. Solids 182 (1995) 257. [9] Z. Hasan, M. Solonenko, P.I. Macfarlane, L. Biyikli, V.K. Mathur, F.A. Karwacki, Appl. Phys. Lett. 72 (1998) 2373. [10] Z. Hasan, L. Biylikli, P.I. Macfarlane, Appl. Phys. Lett. 72 (1998) 3399. [11] R. Reisfeld, E. Greenberg, R.N. Brown, M.G. Drexhage, C.K. Jorgensen, Chem. Phys. Lett. 95 (1983) 91. [12] R.C. Nicklin, J.K. Johnstone, R.G. Barnes, D.R. Wilder, J. Chem. Phys. 59 (1973) 1652. [13] T. Hayakawa, M. Nogami, Solid State Commun. 116 (2000) 77. [14] Miyakawa, D.L. Dexter, Phys. Rev. B 1 (1970) 2961. [15] Y.B. Shin, J. Heo, H.S. Kim, Chem. Phys. Lett. 317 (2000) 637. [16] E.R. Bauminger, D. Froindlich, I. Nowik, S. Ofer, I. Felner, I. Mayer, Phys. Rev. Lett. 30 (1973) 1053. [17] I. Felner, I. Nowik, Physica B 182 (1992) 145.