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Growth and spectroscopic properties of Ho3+ doped Sr3Y2(BO3)4 crystal
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Optical Materials 30 (2008) 1495–1498 www.elsevier.com/locate/optmat
Growth and spectroscopic properties of Ho3+ doped Sr3Y2(BO3)4 crystal Qian Wei a
a,b
, Xiuzhi Li a, Guojian Wang a,b, Mingjun Song Guofu Wang a, Xifa Long a,*
a,b
, Zujian Wang
a,b
,
Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China b Graduate School of the Chinese Academy of Sciences, Beijing 100039, China Received 9 June 2007; received in revised form 1 September 2007; accepted 9 September 2007 Available online 29 October 2007
Abstract The single crystal of Ho3+ doped Sr3Y2(BO3)4 has been grown by the Czochralski method. The absorption spectrum, fluorescence spectrum, and fluorescence decay curve of the crystal were measured at room temperature. The fluorescence spectrum in the range of 450–800 nm is dominated by 5 F 5 ! 5 I 8 and 5S2, 5 F 4 ! 5 I 8 transitions. According to the Judd–Ofelt theory, the intensity parameters Xt (t = 2, 4, 6) were calculated, and the spontaneous transition probabilities, fluorescence branching ratios and radiative lifetimes were obtained. The fluorescence lifetime of the 5 F 5 ! 5 I 8 transition for Ho3+ : Sr3Y2(BO3)4 crystal is about 57 ns. 2007 Elsevier B.V. All rights reserved. PACS: 42.70.Hj; 78.20.-e; 81.10. Fq Keywords: Crystal growth; Ho3+ : Sr3Y2(BO3)4 crystal; Spectroscopic properties
1. Introduction Recently, considerable interest was focused on the solid laser field due to its extensive applications in many fields such as scientific research, military, medicine and so on. The trivalent rare-earth ions (RE) doped materials, such as Nd3+, Er3+, Yb3+ and Tm3+ [1–4], have been of great interest in the past decades. As a member of rare-earth ions family, Ho3+ ion is investigated more and more extensively due to their good laser action in various wavelengths including infrared, visible and ultra-violet regions. Especially, the laser properties of Ho3+ near 2.0 lm resulted from 5 I 7 ! 5 I 8 emission transition have been paid much attention because of the eye-safe range emitting in the solid-state lasers [5]. Furthermore, Ho3+ ions can generate *
Corresponding author. Tel.: +86 591 83710369; fax: +86 591 83714946. E-mail address: [email protected] (X. Long). 0925-3467/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2007.09.005
visible and ultraviolet laser output with a long wavelength pumping by the up-conversion process [6–8]. Ho3+-doped host materials, including crystals, glasses and solutions, have been receiving a great deal of attentions due to their good spectroscopic properties [9–20]. Sr3Y2(BO3)4, a member of SrO–Y2O3–B2O3 ternary system, has been demonstrated to be a promising phosphors host material because of the large band-gap, easy synthesis, chemical and physical stability and so on [21]. Sr3Y2(BO3)4 belongs to the orthorhombic structure with Pc21n space group, and the lattice parameters are as follows: a = ˚ , b = 15.971 A ˚ , c = 7.392 A ˚ , a = b = c = 90 [22]. 8.694 A The spectroscopic properties for Nd3+-doped Sr3Y2(BO3)4 in this matrix has been reported previously [23]. He et al. have also reported the red photoluminescence behavior of Eu3+ : Sr3Y2(BO3)4, showing it is a potential phosphors material [21,22]. This paper reported the crystal growth and the spectroscopic properties of Ho3+ : Sr3Y2(BO3)4 crystal.
1496
Q. Wei et al. / Optical Materials 30 (2008) 1495–1498
2. Experimental The Ho3+ : Sr3Y2(BO3)4 single crystal was grown by the Czochralski method. The start materials, Sr2O3 (99.99%), Y2O3 (99.99%), Ho2O3 (99.99%) and H3BO3 (99.9%), were weighed accurately according to the stoichiometric ratio of Sr3Y1.98Ho0.02(BO3)4 but with 3 wt% excess of H3BO3 in order to compensate the loss of B2O3 volatilization during the growth process. The above materials were mixed, ground, pressed and synthesized by the conventional solid-reaction method. After that, the synthesized material was placed in an iridium (Ir) crucible and melted in a 2.5 kHz frequency induction furnace. A small bar of Sr3Y2(BO3)4 crystal was used as a seed. After repeated seeding trials, the crystal was grown at a pulling rate of 1–2 mm/h and a rotating rate of 15–30 rpm in the N2 atmosphere. At the end, A Ho3+ : Sr3Y2(BO3)4 crystal with dimensions of Ø20 · 25 mm3 was obtained (shown in Fig. 1). The surface of the crystal was opaque because of the corrosion of the volatilized H3BO3 during the growth process. The formation of the as-grown crystal was monitored by means of X-ray diffraction (D-max-rA type diffractometer) with Cu Ka radiation at room temperature. Fig. 2 shows the X-ray diffraction pattern of the as-grown crystal, which is consistent with the reported one in Ref. [22]. The result suggests the composition and structure of the as-grown crystal is Ho3+ : Sr3Y2(BO3)4 crystal. Three equiponderant samples cut from the top, middle, and bottom of the crystal
Fig. 1. As-grown Ho3+ : Sr3Y2(BO3)4 crystal and a polished plate (scale:mm).
Intensity (Counts)
5000 4000
were pulverize to measure the Ho3+ concentration. The average concentration of holmium ions in Sr3Y2(BO3)4 crystal was measured to be 0.35 wt% by the inductively coupled plasma atomic emission spectrometry (ICPAES). Thus the effective segregation coefficient is calculated to be 1.4 by the following formula: K¼
½molesHo=ðmolesHo þ molesYÞcrystal ½molesHo=ðmolesHo þ molesYÞmelt
A crystal plate with dimensions of 11 · 8 · 0.9 mm3, cut from the top of the as-grown crystal, was polished for spectral measurements (as shown in Fig. 2). The room temperature absorption spectrum was measured using a Perking-Elmer UV–Vis–NIR spectrometer (Lambda-900). The fluorescence spectrum and decay curve at room temperature were measured using an Edinburgh Instruments FLS920 spectrophotometer. 3. Results and discussion 3.1. Absorption spectrum Fig. 3a and b shows the absorption spectrum of Ho3+ : Sr3Y2(BO3)4 crystal at room temperature. It can be seen that: (1) In the range of 1000–2300 nm, there are two absorption bands with peaks at 1150 and 1949 nm attributed to 5 I 8 ! 5 I 6 and 5 I 7 transitions of Ho3+ ion (as shown in Fig. 3a). (2) In the range of 200–750 nm, the dominant absorption bands with peaks at 361, 418, 450, 538 and 642 nm are related to the 5 I 8 ! 3 H 5 þ 3 H 6 , ð5 G; 3 GÞ, 5 F 1 þ 5 G6 , 5 S 2 þ 5 F 4 and 5 F 5 transitions, respectively (as shown in Fig. 3b). (3) Moreover, three weak absorption bands corresponding to 5 I 8 ! 3 F 4 , 3 P 0 þ ð3 H ; 1 GÞ4 and ð5 G; 5 D; 3 GÞ4 transitions in the range of 220–310 nm, were also detected due to the absence of large background corrections in the ultraviolet range [24]. The Judd–Ofelt theory [25,26] is an effective method to analyze the optical characteristics of trivalent rare-earth ions in many host materials. Since the application of the J–O theory have been extensively reported previously [27], only the main results were presented as follows: The RMS error is 7.39% and the three intensity parameters Xt (t = 2, 4, 6) were obtained to be X2 = 4.46 · 1020, X4 = 1.47 · 1020 and X6 = 2.11 · 1020 cm2. 3.2. Fluorescence spectrum
3000 2000 1000 0 10
20
30
40
50
60
70
2θ (deg.) Fig. 2. X-ray diffraction pattern of Ho3+ : Sr3Y2(BO3)4 crystal.
80
Fig. 4 shows the fluorescence spectrum at room temperature. It is composed of four emission bands corresponding to 5 F 3 ! 5 I 8 (500 nm), 5 F 4 ; 5 S 2 ! 5 I 8 (547 nm), 5 F 5 ! 5 I 8 (661 nm) and 5 S 2 ! 5 I 7 (755 nm) transitions, respectively. In the visible range, the 5 F 5 ! 5 I 8 transition with a peak at 661 nm is the strongest emission, which is consistent with the calculated results based on the Judd–Ofelt theory. Based on the determined intensity parameters, the spontaneous transition probabilities, fluorescence branching
Q. Wei et al. / Optical Materials 30 (2008) 1495–1498
a
b Absorption coefficient (cm-1)
Absorption coefficient (cm-1)
1.0 0.8 0.6 0.4 0.2 0.0 1000
1500
2.5 2.0 1.5 1.0 0.5 0.0 200
2000
1497
300
400
500
600
700
Wavelength (nm)
Wavelength (nm)
Fig. 3. Absorption spectrum of Ho3+ : Sr3Y2(BO3)4 at room temperature: (a) in the range of 1000–2300 nm; (b) in the range of 200–750 nm.
30000 5
5
1
I8
25000
20000 5
5
F4, S2
15000
Log(I/I0)
Fluorescence intensity (a.u.)
F5
5
I8
0.1
10000 5 5
5000
5
F 3 I8
5
S 2 I7
0.01
0 500
600
700
150
800
Fig. 4. Fluorescence spectrum of Ho3+ : Sr3Y2(BO3)4 crystal at room temperature under excitation at 450 nm.
ratios and radiative lifetimes for Ho3+ : Sr3Y2(BO3)4 crystal were calculated and presented in Table 1.
Table 1 Luminescence parameters of Ho3+ : Sr3Y2(BO3)4 crystal Transition
A (aJ, aJ 0 ) (s1)
b
Lifetime (ms)
5
3330 873 216 18.3 11.2 7650 534 470 305 58.7 17.8 3380 2320 392 106 109 73.8
0.750 0.197 0.0487 0.00414 0.0000256 0.847 0.591 0.052 0.0338 0.00649 0.00208 0.536 0.368 0.0621 0.0168 0.0172 0.000117
0.363
5
F 5 ! I8 ! 5I7 ! 5I6 ! 5I5 ! 5I4 5 F 4 ! 5I8 ! 5I7 ! 5I6 ! 5I5 ! 5I4 ! 5F 5 5 S2 ! 5 I 8 ! 5I7 ! 5I6 ! 5I5 ! 5I4 ! 5F 5
200
250
Time (ns)
Wavelength (nm)
0.181
0.260
Fig. 5. Fluorescence decay curve of Ho3+ : Sr3Y2(BO3)4 excited by 450 nm pumping.
Fig. 5 shows the fluorescence decay curve of the F 5 ! 5 I 8 transition at room temperature. The linear relationship suggests a single exponential behavior of the fluorescence decay. The fluorescence lifetime was fitted to be 57 ns, which is much lower than the radiative lifetime due to the high-energy phonons associated with the (BO3) group in Ho3+ : Sr3Y2(BO3)4 crystal [28]. 5
4. Conclusions The single crystal of Ho3+ doped Sr3Y2(BO3)4 was successfully grown by the Czochralski technique. The spectral properties of Ho3+ doped Sr3Y2(BO3)4 crystal at room temperature were investigated. Based on the Judd– Ofelt theory, the intensity parameters were calculated to be X2 = 4.66 · 1020, X4 = 1.47 · 1020, X6 = 2.11 · S1020 cm2, and the spontaneous transition probabilities, fluorescence branching ratios and radiative lifetimes were obtained. The dominant features of visible emission spectrum are two stronger emission bands resulted from 5 F 5 ! 5 I 8 and 5 F 4 ; 5 S 2 ! 5 I 8 transitions, respectively. The fluorescence lifetime of the 5 F 5 ! 5 I 8 transition for Ho3+ : Sr3Y2(BO3)4 crystal is about 57 ns.
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Q. Wei et al. / Optical Materials 30 (2008) 1495–1498
Acknowledgement This work is supported by the Young Scientists Innovation Foundation of Fujian Province (2003J041 and 2006F3139). References [1] Y. Lu, G.F. Wang, J. Cryst. Growth 253 (2003) 270. [2] M.J. Weber, Phys. Rev. 157 (1967) 262. [3] L.F. Johson, H.G. Guggenheim, T.C. Rich, F.W. Ostermayer, J. Appl. Phys. 43 (1972) 1125. [4] E. Sani, A. Toncelli, M. Tonelli, N. Coluccelli, G. Galzerano, P. Laporta, J. Appl. Phys. B 81 (2005) 847. [5] L.C. Courrol, L. Gomes, S.P. Morato, Phys. Rev. 51 (1995) 3344. [6] V. Lavı´n, F. Lahoz, I.R. Martı´n, U.R. Rodrı´guez-Mendoza, J.M. Ca´ceres, Opt. Mater. 27 (2005) 1754. [7] Ch. Liu, J. Heo, J. Non-Cryst. Solids 352 (2006) 5325. [8] A.K. Singh, S.B. Rai, V.B. Singh, J. Alloy. Compd. 403 (2005) 97. [9] Y. Yang, B. Yao, B. Chen, Ch. Wang, G. Ren, X. Wang, Opt. Mater. 29 (2007) 1159. [10] I. Fo¨ldva´ri, A. Baraldi, R. Capelletti, Magnani N, R. Sosa F, A. Munoz F, L.A. Kappers, A. Watterich, Opt. Mater. 29 (2007) 688. [11] W. Xu, X. Xu, J. Wang, F. Wu, L. Su, G. Zhao, Zh. Zhao, G. Zhou, J. Xu, J. Alloys. Compds. 440 (2007) 319.
[12] M. True, Y. Chen, M. Kirm, S. Vielhauer, G. Zimmerer, J. Lumin. 124 (2007) 279. [13] Z. Wang, Y. Yin, D. Yuan, J. Alloy. Compd. 436 (2007) 364. [14] A. Florez, S.L. Oliveira, M. Flo´rez, L.A. Go´mez, L.A.O. Nunes, J. Alloy. Compd. 418 (2006) 238. [15] N.S. Hussain, N. Ali, A.G. Dias, M.A. Lopes, J.D. Santos, S. Buddhudu, Thin Solid Films 515 (2006) 318. [16] V.K. Tikhomirov, J. Me´ndez-Ramos, V.D. Rodrı´guez, D. Furniss, A.B. Seddon, J. Alloy. Compd. 436 (2007) 216. [17] L. Feng, J. Wang, Q. Tang, L. Liang, H. Liang, Q. Su, J. Lumin. 124 (2007) 187. [18] D.E. Henrie, R.L. Fellows, G.R. Choppin, Coord. Chem. Rev. 18 (1976) 199. [19] K.B. Yatsimirskii, N.K. Davidenko, Coord. Chem. Rev. 27 (1979) 223. [20] W.T. Carnall, P.R. Fields, K. Rajnak, J. Chem. Phys. 49 (1968) 4412. [21] L. He, Y. Wang, J. Alloy. Compd. 431 (2007) 226. [22] Y. Zhang, Y. Li, J. Alloy. Compd. 384 (2004) 88. [23] Y. Zhang, Zh. Lin, Z. Hu, G. Wang, J. Solid State Chem. 177 (2004) 3183. [24] W.T. Carnall, P.R. Fields, K. Rajnak, J. Chem. Phys. 49 (1968) 4424. [25] G.S. Ofelt, J. Chem. Phys. 37 (1962) 511. [26] B.R. Judd, Phys. Rev. 127 (1963) 750. [27] E.B. Dunina, A.A. Kaminskii, A.A. Kornienko, K. Kurbanov, K.K. Pukhov, Sov. Phys. Solid State 57 (1990) 562. [28] D. Jaque, M.O. Ramirez, L.E. Bausa´, J. Garcı´a Sole´, E. Cavalli, A. Speghini, M. Bettinelli, Phys. Rev. B 68 (2003) 035118.
Optical Materials 30 (2008) 1495–1498 www.elsevier.com/locate/optmat
Growth and spectroscopic properties of Ho3+ doped Sr3Y2(BO3)4 crystal Qian Wei a
a,b
, Xiuzhi Li a, Guojian Wang a,b, Mingjun Song Guofu Wang a, Xifa Long a,*
a,b
, Zujian Wang
a,b
,
Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China b Graduate School of the Chinese Academy of Sciences, Beijing 100039, China Received 9 June 2007; received in revised form 1 September 2007; accepted 9 September 2007 Available online 29 October 2007
Abstract The single crystal of Ho3+ doped Sr3Y2(BO3)4 has been grown by the Czochralski method. The absorption spectrum, fluorescence spectrum, and fluorescence decay curve of the crystal were measured at room temperature. The fluorescence spectrum in the range of 450–800 nm is dominated by 5 F 5 ! 5 I 8 and 5S2, 5 F 4 ! 5 I 8 transitions. According to the Judd–Ofelt theory, the intensity parameters Xt (t = 2, 4, 6) were calculated, and the spontaneous transition probabilities, fluorescence branching ratios and radiative lifetimes were obtained. The fluorescence lifetime of the 5 F 5 ! 5 I 8 transition for Ho3+ : Sr3Y2(BO3)4 crystal is about 57 ns. 2007 Elsevier B.V. All rights reserved. PACS: 42.70.Hj; 78.20.-e; 81.10. Fq Keywords: Crystal growth; Ho3+ : Sr3Y2(BO3)4 crystal; Spectroscopic properties
1. Introduction Recently, considerable interest was focused on the solid laser field due to its extensive applications in many fields such as scientific research, military, medicine and so on. The trivalent rare-earth ions (RE) doped materials, such as Nd3+, Er3+, Yb3+ and Tm3+ [1–4], have been of great interest in the past decades. As a member of rare-earth ions family, Ho3+ ion is investigated more and more extensively due to their good laser action in various wavelengths including infrared, visible and ultra-violet regions. Especially, the laser properties of Ho3+ near 2.0 lm resulted from 5 I 7 ! 5 I 8 emission transition have been paid much attention because of the eye-safe range emitting in the solid-state lasers [5]. Furthermore, Ho3+ ions can generate *
Corresponding author. Tel.: +86 591 83710369; fax: +86 591 83714946. E-mail address: [email protected] (X. Long). 0925-3467/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2007.09.005
visible and ultraviolet laser output with a long wavelength pumping by the up-conversion process [6–8]. Ho3+-doped host materials, including crystals, glasses and solutions, have been receiving a great deal of attentions due to their good spectroscopic properties [9–20]. Sr3Y2(BO3)4, a member of SrO–Y2O3–B2O3 ternary system, has been demonstrated to be a promising phosphors host material because of the large band-gap, easy synthesis, chemical and physical stability and so on [21]. Sr3Y2(BO3)4 belongs to the orthorhombic structure with Pc21n space group, and the lattice parameters are as follows: a = ˚ , b = 15.971 A ˚ , c = 7.392 A ˚ , a = b = c = 90 [22]. 8.694 A The spectroscopic properties for Nd3+-doped Sr3Y2(BO3)4 in this matrix has been reported previously [23]. He et al. have also reported the red photoluminescence behavior of Eu3+ : Sr3Y2(BO3)4, showing it is a potential phosphors material [21,22]. This paper reported the crystal growth and the spectroscopic properties of Ho3+ : Sr3Y2(BO3)4 crystal.
1496
Q. Wei et al. / Optical Materials 30 (2008) 1495–1498
2. Experimental The Ho3+ : Sr3Y2(BO3)4 single crystal was grown by the Czochralski method. The start materials, Sr2O3 (99.99%), Y2O3 (99.99%), Ho2O3 (99.99%) and H3BO3 (99.9%), were weighed accurately according to the stoichiometric ratio of Sr3Y1.98Ho0.02(BO3)4 but with 3 wt% excess of H3BO3 in order to compensate the loss of B2O3 volatilization during the growth process. The above materials were mixed, ground, pressed and synthesized by the conventional solid-reaction method. After that, the synthesized material was placed in an iridium (Ir) crucible and melted in a 2.5 kHz frequency induction furnace. A small bar of Sr3Y2(BO3)4 crystal was used as a seed. After repeated seeding trials, the crystal was grown at a pulling rate of 1–2 mm/h and a rotating rate of 15–30 rpm in the N2 atmosphere. At the end, A Ho3+ : Sr3Y2(BO3)4 crystal with dimensions of Ø20 · 25 mm3 was obtained (shown in Fig. 1). The surface of the crystal was opaque because of the corrosion of the volatilized H3BO3 during the growth process. The formation of the as-grown crystal was monitored by means of X-ray diffraction (D-max-rA type diffractometer) with Cu Ka radiation at room temperature. Fig. 2 shows the X-ray diffraction pattern of the as-grown crystal, which is consistent with the reported one in Ref. [22]. The result suggests the composition and structure of the as-grown crystal is Ho3+ : Sr3Y2(BO3)4 crystal. Three equiponderant samples cut from the top, middle, and bottom of the crystal
Fig. 1. As-grown Ho3+ : Sr3Y2(BO3)4 crystal and a polished plate (scale:mm).
Intensity (Counts)
5000 4000
were pulverize to measure the Ho3+ concentration. The average concentration of holmium ions in Sr3Y2(BO3)4 crystal was measured to be 0.35 wt% by the inductively coupled plasma atomic emission spectrometry (ICPAES). Thus the effective segregation coefficient is calculated to be 1.4 by the following formula: K¼
½molesHo=ðmolesHo þ molesYÞcrystal ½molesHo=ðmolesHo þ molesYÞmelt
A crystal plate with dimensions of 11 · 8 · 0.9 mm3, cut from the top of the as-grown crystal, was polished for spectral measurements (as shown in Fig. 2). The room temperature absorption spectrum was measured using a Perking-Elmer UV–Vis–NIR spectrometer (Lambda-900). The fluorescence spectrum and decay curve at room temperature were measured using an Edinburgh Instruments FLS920 spectrophotometer. 3. Results and discussion 3.1. Absorption spectrum Fig. 3a and b shows the absorption spectrum of Ho3+ : Sr3Y2(BO3)4 crystal at room temperature. It can be seen that: (1) In the range of 1000–2300 nm, there are two absorption bands with peaks at 1150 and 1949 nm attributed to 5 I 8 ! 5 I 6 and 5 I 7 transitions of Ho3+ ion (as shown in Fig. 3a). (2) In the range of 200–750 nm, the dominant absorption bands with peaks at 361, 418, 450, 538 and 642 nm are related to the 5 I 8 ! 3 H 5 þ 3 H 6 , ð5 G; 3 GÞ, 5 F 1 þ 5 G6 , 5 S 2 þ 5 F 4 and 5 F 5 transitions, respectively (as shown in Fig. 3b). (3) Moreover, three weak absorption bands corresponding to 5 I 8 ! 3 F 4 , 3 P 0 þ ð3 H ; 1 GÞ4 and ð5 G; 5 D; 3 GÞ4 transitions in the range of 220–310 nm, were also detected due to the absence of large background corrections in the ultraviolet range [24]. The Judd–Ofelt theory [25,26] is an effective method to analyze the optical characteristics of trivalent rare-earth ions in many host materials. Since the application of the J–O theory have been extensively reported previously [27], only the main results were presented as follows: The RMS error is 7.39% and the three intensity parameters Xt (t = 2, 4, 6) were obtained to be X2 = 4.46 · 1020, X4 = 1.47 · 1020 and X6 = 2.11 · 1020 cm2. 3.2. Fluorescence spectrum
3000 2000 1000 0 10
20
30
40
50
60
70
2θ (deg.) Fig. 2. X-ray diffraction pattern of Ho3+ : Sr3Y2(BO3)4 crystal.
80
Fig. 4 shows the fluorescence spectrum at room temperature. It is composed of four emission bands corresponding to 5 F 3 ! 5 I 8 (500 nm), 5 F 4 ; 5 S 2 ! 5 I 8 (547 nm), 5 F 5 ! 5 I 8 (661 nm) and 5 S 2 ! 5 I 7 (755 nm) transitions, respectively. In the visible range, the 5 F 5 ! 5 I 8 transition with a peak at 661 nm is the strongest emission, which is consistent with the calculated results based on the Judd–Ofelt theory. Based on the determined intensity parameters, the spontaneous transition probabilities, fluorescence branching
Q. Wei et al. / Optical Materials 30 (2008) 1495–1498
a
b Absorption coefficient (cm-1)
Absorption coefficient (cm-1)
1.0 0.8 0.6 0.4 0.2 0.0 1000
1500
2.5 2.0 1.5 1.0 0.5 0.0 200
2000
1497
300
400
500
600
700
Wavelength (nm)
Wavelength (nm)
Fig. 3. Absorption spectrum of Ho3+ : Sr3Y2(BO3)4 at room temperature: (a) in the range of 1000–2300 nm; (b) in the range of 200–750 nm.
30000 5
5
1
I8
25000
20000 5
5
F4, S2
15000
Log(I/I0)
Fluorescence intensity (a.u.)
F5
5
I8
0.1
10000 5 5
5000
5
F 3 I8
5
S 2 I7
0.01
0 500
600
700
150
800
Fig. 4. Fluorescence spectrum of Ho3+ : Sr3Y2(BO3)4 crystal at room temperature under excitation at 450 nm.
ratios and radiative lifetimes for Ho3+ : Sr3Y2(BO3)4 crystal were calculated and presented in Table 1.
Table 1 Luminescence parameters of Ho3+ : Sr3Y2(BO3)4 crystal Transition
A (aJ, aJ 0 ) (s1)
b
Lifetime (ms)
5
3330 873 216 18.3 11.2 7650 534 470 305 58.7 17.8 3380 2320 392 106 109 73.8
0.750 0.197 0.0487 0.00414 0.0000256 0.847 0.591 0.052 0.0338 0.00649 0.00208 0.536 0.368 0.0621 0.0168 0.0172 0.000117
0.363
5
F 5 ! I8 ! 5I7 ! 5I6 ! 5I5 ! 5I4 5 F 4 ! 5I8 ! 5I7 ! 5I6 ! 5I5 ! 5I4 ! 5F 5 5 S2 ! 5 I 8 ! 5I7 ! 5I6 ! 5I5 ! 5I4 ! 5F 5
200
250
Time (ns)
Wavelength (nm)
0.181
0.260
Fig. 5. Fluorescence decay curve of Ho3+ : Sr3Y2(BO3)4 excited by 450 nm pumping.
Fig. 5 shows the fluorescence decay curve of the F 5 ! 5 I 8 transition at room temperature. The linear relationship suggests a single exponential behavior of the fluorescence decay. The fluorescence lifetime was fitted to be 57 ns, which is much lower than the radiative lifetime due to the high-energy phonons associated with the (BO3) group in Ho3+ : Sr3Y2(BO3)4 crystal [28]. 5
4. Conclusions The single crystal of Ho3+ doped Sr3Y2(BO3)4 was successfully grown by the Czochralski technique. The spectral properties of Ho3+ doped Sr3Y2(BO3)4 crystal at room temperature were investigated. Based on the Judd– Ofelt theory, the intensity parameters were calculated to be X2 = 4.66 · 1020, X4 = 1.47 · 1020, X6 = 2.11 · S1020 cm2, and the spontaneous transition probabilities, fluorescence branching ratios and radiative lifetimes were obtained. The dominant features of visible emission spectrum are two stronger emission bands resulted from 5 F 5 ! 5 I 8 and 5 F 4 ; 5 S 2 ! 5 I 8 transitions, respectively. The fluorescence lifetime of the 5 F 5 ! 5 I 8 transition for Ho3+ : Sr3Y2(BO3)4 crystal is about 57 ns.
1498
Q. Wei et al. / Optical Materials 30 (2008) 1495–1498
Acknowledgement This work is supported by the Young Scientists Innovation Foundation of Fujian Province (2003J041 and 2006F3139). References [1] Y. Lu, G.F. Wang, J. Cryst. Growth 253 (2003) 270. [2] M.J. Weber, Phys. Rev. 157 (1967) 262. [3] L.F. Johson, H.G. Guggenheim, T.C. Rich, F.W. Ostermayer, J. Appl. Phys. 43 (1972) 1125. [4] E. Sani, A. Toncelli, M. Tonelli, N. Coluccelli, G. Galzerano, P. Laporta, J. Appl. Phys. B 81 (2005) 847. [5] L.C. Courrol, L. Gomes, S.P. Morato, Phys. Rev. 51 (1995) 3344. [6] V. Lavı´n, F. Lahoz, I.R. Martı´n, U.R. Rodrı´guez-Mendoza, J.M. Ca´ceres, Opt. Mater. 27 (2005) 1754. [7] Ch. Liu, J. Heo, J. Non-Cryst. Solids 352 (2006) 5325. [8] A.K. Singh, S.B. Rai, V.B. Singh, J. Alloy. Compd. 403 (2005) 97. [9] Y. Yang, B. Yao, B. Chen, Ch. Wang, G. Ren, X. Wang, Opt. Mater. 29 (2007) 1159. [10] I. Fo¨ldva´ri, A. Baraldi, R. Capelletti, Magnani N, R. Sosa F, A. Munoz F, L.A. Kappers, A. Watterich, Opt. Mater. 29 (2007) 688. [11] W. Xu, X. Xu, J. Wang, F. Wu, L. Su, G. Zhao, Zh. Zhao, G. Zhou, J. Xu, J. Alloys. Compds. 440 (2007) 319.
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