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The organic ligands coordinated long afterglow phosphor
Materials Letters 61 (2007) 3185 – 3188 www.elsevier.com/locate/matlet
The organic ligands coordinated long afterglow phosphor Suli Wu, Shufen Zhang ⁎, Yu Liu, Jinzong Yang State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116012, China Received 10 May 2006; accepted 5 November 2006 Available online 27 November 2006
Abstract The Eu2+ activated strontium aluminates codoped by Dy3+ coordinated by different ligands were synthesized. The coordination of ligands with SAO-ED was characterized by FT-IR spectra and XPS. The introduction of organic ligands didn't change the excitation and emission spectra of SAO-ED, and this was proved by spectrophotometer (F-4500 FL) at room temperature. The organic ligands coordinated SAO-ED has good brightness and long decay time measured with spectrometer (Konica Minolta LS-100) and higher water resistance than that of SAO-ED. © 2006 Elsevier B.V. All rights reserved. Keywords: Strontium aluminate; Coordinated; Ligands
1. Introduction Recently, much research on organic–inorganic hybrid materials is strongly motivated by their extraordinary properties in many fields of applications as they combine the mutual advantages of both organic and inorganic networks [1,2]. The Eu2+ activated strontium aluminate codoped by Dy3+ (SAOED) is widely used for such diverse “glow-in-the-dark ” items as golf balls, rubber shoe soles, a variety of toys, direction indicators and signs and the like due to its better and safe, chemically stable, very bright and long-lasting afterglow with no radiation [3]. But these phosphors are sensitive to environmental moisture and have poor compatibility with organics or polymers. When inorganic phosphor was used in polymer, it is difficult to obtain a homogeneous dispersion of the particles in the polymer matrix. Introducing hydrophobic organics onto the surface of aluminate phosphors will increase their stability and compatibility with organics. To attempt to overcome the above problems, physical or chemical modifications have been made on the surface of rareearth ions activated alkali earth aluminate phosphors. Inorganic oxides such as SiO2, AlO3 were introduced onto the surface of
⁎ Corresponding author. Fax: +86 411 88993621. E-mail address: [email protected] (S. Zhang). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.11.019
aluminate phosphors to increase their stability [4], but this method can't improve the compatibility with organics. Resins [5] and organic compounds with both hydrophobic and hydrophilic groups [6] were also used to modify the surface properties of inorganic phosphor. Although the above methods can increase the stability and compatibility of aluminate phosphors with organics in some degree, the interaction between the coating layer and phosphor's surface was only caused by hydrogen bonding or Van der waals forces which belong to physisorption. Therefore, the obtained films are often thermally unstable. A much stronger adhesion between the organics or polymers and the substrate is achieved if the organics are chemically bonded to the surface. Organic compounds were usually introduced onto the inorganic particles through binder which could react with hydroxyl groups on the surface of inorganic particles. However, there are few active groups as hydroxyl groups on the surface of dried SAO-ED particles used in the present work. The luminescence properties would decrease if there are hydroxyl groups on the surface of SAO-ED particles at the existence of water. So the method using binder with active groups that can react with hydroxyl groups to combine organic compound with inorganic particles was not suitable in this study, whereas there are unsaturated Sr2+, Al3+, Eu2+ and Dy3+ ions on the surface of SAO-ED particles that have activity. In the present work, β-diketones, multi-carboxylic acids and heterocyclic compounds that have two or more
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Scheme 1. Ligands coordinated with metal ions on the surface of SAO-ED.
coordinative groups were used to coordinate with the active ions on the surface of inorganic particles. 2. Experimental SAO-ED phosphors were synthesized using sol-gel–microwave process in our laboratory. Ligand (1,10-phenanthroline, 8hydroxyquinoline, acetyl acetone, citric acid, tartaric acid) was dissolved in ethanol. SAO-ED particles prepared by sol-gel– microwave method were added to the above solution slowly when being stirred with high-speed. The pH value was controlled at 8–9 and span-80 was added as surfactant. The mixture was stirred at 40–45 °C for 3 h. Then the mixture was filtered and washed with water and ethanol for several times and then dried. Each sample was analyzed by FT-IR and XPS. The infrared spectrum was recorded on a KBr pressed disk. The excitation and emission spectra were recorded on spectrophotometer (F-4500 FL) at room temperature. The brightness and decay time were measured with spectrometer (Konica Minolta LS-100). Spectral resolution of the spectrometers is ±2% during 0.001–0.999 cd/m2, ± 1% when N 0.999 cd/m2. 3. Results and discussion Organic compounds containing O, N, F, Cl, etc. atoms which can provide electrons can coordinate with unsaturated metal ions. Sr2+, Al3+, Eu2+ and Dy3+ ions inside the SAO-ED particles are saturated by coordinating with O2−, but these ions on the surface of SAO-ED particles are unsaturated, so they are reactive, can coordinate with organic compounds. In the present work, in order to form a firm coordinate bond, organic compounds that have two or more coordinate groups were adopted to coordinate with SAO-ED particles (CD-SAO-ED) (as Scheme 1 shows).
β-diketones [7], multi-carboxylic acids [8] and heterocyclic compounds [9] are chelating reagents and have been reported as ligands to prepare phosphors. Acetyl acetone, citric acid, tartaric acid, 1, 10-phenanthroline (phen) and 8-hydroxyquinoline were selected in the present work to coordinate with SAO-ED in ethanol at the presence of span-80 with high-speed stir. The coordination of ligands with SAOED was characterized by FT-IR spectra .The absorbance of the ligands coordinated with SAO-ED arising from carbonyl group shifted to a lower frequency than that of the corresponding free ligand (as Table 1 showed). After coordinated with metal ions, the lone electron pair of oxygen atom in C_O group or C–O transferred to the shell orbit of metal ions partly. This causes the decrease of C–O bond energy and forms the stable conjugated ring. The conjugated effect made the absorbance arising from the carbonyl group to shift to a lower frequency. As to 8-hydroxyquinoline and 1, 10-phenanthroline, the absorbance arising from C_C also shifted to a lower frequency due to a conjugated effect. The stretching vibration in the complexes is shifted to a lower frequency lower than that of the corresponding free ligand, which indicated that the coordination of these subunits to the ions occurred in the complexes. These values are in good agreement with the literature data [10]. Moreover, the presence of coordinated ligands on the surface of SAO-ED particles was confirmed by signals arising from the carbon (285 eV, C(1s-1); 287 eV, C(1s-2); 290 eV, C(1s-3)). Indeed, in the experiment the Al(2p) signals act as a marker for the SAO-ED particles and all of the C(1s) signals arise from the surface coordinated APD molecules (a small part of the signals is also from carbon of contamination). The excitation and emission spectra of SAO-ED particles coordinated with acetyl acetone, citric acid, tartaric acid, 1, 10phenanthroline (phen) and 8-hydroxyquinoline were recorded and compared with that of SAO-ED particles. The introduction of organic ligands didn't affect the luminescent properties greatly, as Figs. 1 and 2 show, and the excitation and emission spectra of the SAO-ED particle are similar with that of samples coordinated with the above ligands in peak intensity and peak shape. Each sample has only one emission peak centered at 519 nm under the excitation of 323 nm wavelength, as
Table 1 The characteristic FT-IR absorbance of free ligands and the ligands coordinated with SAO-ED Wavelength of free ligand/cm− 1 Wavelength of ligand after coordination/ cm− 1 Functional group
Citric acid
Tartaric acid
Acetyl acetone
8-hydroxyquinoline
1, 10-phenanthroline
1732 1716 Vibration of C_O
1746 1709 Vibration of C_O
1720 1680 Vibration of C_O
1507 1460 Vibration of C_C
1475 1456 Vibration of C_C
S. Wu et al. / Materials Letters 61 (2007) 3185–3188
Fig. 1. The emission spectra of SAO-ED material and SAO-ED coordinated with different ligands.
a result of the 5d to 4f transition of Eu2+ ions in SrAl2O4. This is due to the fact that the amount of Eu2+ ions coordinated with ligands is limited (ligands may coordinate with other metal ions on the surface of SAOED), which leads to the ligand-to-metal charge-transfer transition to be very weak, and the emission and excitation intensity of Eu2+ ions in SrAl2O4 is strong, so the effect of ligands on the emission and excitation is not obvious. Therefore the spectra mainly reflect the characteristic emission and excitation of Eu2+ ions in SrAl2O4. Table 2 shows the brightness of SAO-ED and SAO-ED coordinated by different ligands after excitation. We can see that the introduction of organic ligands affects the luminescence properties slightly. Especially, the brightness of phen and acetyl acetone coordinated SAO-ED particles was slightly higher than that of SAO-ED particles. This may be due to the “antenna effect”. The absorption coefficients of organic chromophores are typically orders of magnitude higher than those of rare-earth ions [11], and, when photoexcitation is accompanied by efficient exciton transfer to the rare-earth ion, this provides an efficient mechanism for sensitizing the characteristic rare-earth emission—a mechanism often called the “antenna effect” [12]. The brightness decreased when citric acid and tartaric acid were introduced, and this may be due to the hydrolysis of SAO-ED particles under acidic atmosphere. The reason for the decrease of the brightness when the 8-hydroxyquinoline was introduced is the coordination of 8-hydroxyquinoline with Al3+
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Fig. 2. The excitation spectra of SAO-ED material and SAO-ED coordinated with different ligands.
which destroys the crystal structure of SAO-ED, and this was proved by the decrease of the diameter of SAO-ED particles and the existence of free aluminum tris-8-hydroxyquinoline. The water resistance of organic ligands coordinated SAO-ED and unmodified SAO-ED was investigated at the same condition (2 g of samples was added into 60 ml water respectively and stirred). The Table 2 Brightness (m cd/m2) of SAO-ED and SAO-ED coordinated by different ligands after excitation SAOED 1 1009 2 622 3 451 4 351 5 289 6 243 7 212 8 185 9 166 10 147 20 74 30 48
Citric acid
Tartaric acid
Acetyl acetone
phen
8-hydro xyquinoline
886 548 400 316 257 219 190 166 148 135 67 45
801 492 356 311 251 208 178 157 140 124 58 39
1025 624 456 351 287 245 209 184 166 150 74 47
1028 624 458 353 287 248 213 184 166 152 74 47
933 571 415 324 266 222 195 169 152 137 67 44
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unmodified SAO-ED hydrolyzed completely in 8 h, while organic ligands coordinated SAO-ED hydrolyzed completely in 96 h. This suggests that the introduction of organic ligands increased the water resistance of SAO-ED. The compatibility of organic ligands coordinated SAO-ED and unmodified SAO-ED was also investigated at the same condition (2 g of samples was added into 20 ml ethyl acetate respectively and stirred).
4. Conclusion In conclusion, a yellow-green (emission at about 520 nm) organic–inorganic combined long afterglow phosphor was synthesized by coordinating a ligand with SAO-ED in solvents. This method can be applied to other organic–inorganic hybrid materials and is commonly applicable to prepare organic– inorganic hybrid materials for various requirements. High brightness and long decay time that are a little higher than inorganic SAO-ED were obtained. The combined phosphor had better water resistance than that of SAO-ED and good miscibility with organic compound. Acknowledgements This work was supported by the National Nature Foundation of China (No. 20476016).
References [1] [2] [3] [4] [5] [6] [7] [8]
[9]
[10] [11] [12]
A.P. Alivisatos, Science 271 (1996) 933. S. Förster, M. Antonietti, Adv. Mater. 10 (1998) 195. L. Tracy, L. Phillips, A. Jerry, et al. [P]. 1981,US 6375864. P.D. Friederike, B. Michael, O. Joachim, et al. [P]. 2000,US 6013979. Uejima Koichi, Tachiki Hideyasu, [P]. 1997, JP09125056. Kono Akiteru, [P]. 1997, JP09003449. K. Binnemans, P. Lenaerts, K. Driesen, C. Görller-Walrand, J. Mater. Chem. 14 (2004) 191–195. [19a] F.Y. Liu, L.S. Fu, J. Wang, Z. Liu, H.R. Li, H.J. Zhang, Thin Solid Films 419 (2002) 178–182; [19b] D.W. Dong, S.C. Jiang, Y.F. Men, X.L. Ji, B.Z. Jiang, Adv. Mater. 12 (2000) 646–649. [20a] H.R. Li, J. Lin, H.J. Zhang, L.S. Fu, Q.G. Meng, S.B. Wang, Chem. Mater. 14 (2002) 3651–3655; [20b] A.C. Franville, D. Zambon, R. Mahiou, Chem. Mater. 12 (2000) 428–435; [20c] F. Embert, A. Mehdi, C. Reyé, et al., Chem. Mater. 13 (2001) 4542–4549. D.R. Cousins, F.A.J. Hart, Inorg. Nucl. Chem. 29 (1967) 1745. L.H. Sloof, A. Polman, S.I. Klink, G.A. Hebbink, L. Grave, F.C.J.M. van Veggel, D.N. Reinhoudt, J.W. Hofstraat, Opt. Mater. 14 (2000) 101. J.M. Lehn, Angew. Chem., Int. Ed. Engl. 29 (1990) 1304.
The organic ligands coordinated long afterglow phosphor Suli Wu, Shufen Zhang ⁎, Yu Liu, Jinzong Yang State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116012, China Received 10 May 2006; accepted 5 November 2006 Available online 27 November 2006
Abstract The Eu2+ activated strontium aluminates codoped by Dy3+ coordinated by different ligands were synthesized. The coordination of ligands with SAO-ED was characterized by FT-IR spectra and XPS. The introduction of organic ligands didn't change the excitation and emission spectra of SAO-ED, and this was proved by spectrophotometer (F-4500 FL) at room temperature. The organic ligands coordinated SAO-ED has good brightness and long decay time measured with spectrometer (Konica Minolta LS-100) and higher water resistance than that of SAO-ED. © 2006 Elsevier B.V. All rights reserved. Keywords: Strontium aluminate; Coordinated; Ligands
1. Introduction Recently, much research on organic–inorganic hybrid materials is strongly motivated by their extraordinary properties in many fields of applications as they combine the mutual advantages of both organic and inorganic networks [1,2]. The Eu2+ activated strontium aluminate codoped by Dy3+ (SAOED) is widely used for such diverse “glow-in-the-dark ” items as golf balls, rubber shoe soles, a variety of toys, direction indicators and signs and the like due to its better and safe, chemically stable, very bright and long-lasting afterglow with no radiation [3]. But these phosphors are sensitive to environmental moisture and have poor compatibility with organics or polymers. When inorganic phosphor was used in polymer, it is difficult to obtain a homogeneous dispersion of the particles in the polymer matrix. Introducing hydrophobic organics onto the surface of aluminate phosphors will increase their stability and compatibility with organics. To attempt to overcome the above problems, physical or chemical modifications have been made on the surface of rareearth ions activated alkali earth aluminate phosphors. Inorganic oxides such as SiO2, AlO3 were introduced onto the surface of
⁎ Corresponding author. Fax: +86 411 88993621. E-mail address: [email protected] (S. Zhang). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.11.019
aluminate phosphors to increase their stability [4], but this method can't improve the compatibility with organics. Resins [5] and organic compounds with both hydrophobic and hydrophilic groups [6] were also used to modify the surface properties of inorganic phosphor. Although the above methods can increase the stability and compatibility of aluminate phosphors with organics in some degree, the interaction between the coating layer and phosphor's surface was only caused by hydrogen bonding or Van der waals forces which belong to physisorption. Therefore, the obtained films are often thermally unstable. A much stronger adhesion between the organics or polymers and the substrate is achieved if the organics are chemically bonded to the surface. Organic compounds were usually introduced onto the inorganic particles through binder which could react with hydroxyl groups on the surface of inorganic particles. However, there are few active groups as hydroxyl groups on the surface of dried SAO-ED particles used in the present work. The luminescence properties would decrease if there are hydroxyl groups on the surface of SAO-ED particles at the existence of water. So the method using binder with active groups that can react with hydroxyl groups to combine organic compound with inorganic particles was not suitable in this study, whereas there are unsaturated Sr2+, Al3+, Eu2+ and Dy3+ ions on the surface of SAO-ED particles that have activity. In the present work, β-diketones, multi-carboxylic acids and heterocyclic compounds that have two or more
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Scheme 1. Ligands coordinated with metal ions on the surface of SAO-ED.
coordinative groups were used to coordinate with the active ions on the surface of inorganic particles. 2. Experimental SAO-ED phosphors were synthesized using sol-gel–microwave process in our laboratory. Ligand (1,10-phenanthroline, 8hydroxyquinoline, acetyl acetone, citric acid, tartaric acid) was dissolved in ethanol. SAO-ED particles prepared by sol-gel– microwave method were added to the above solution slowly when being stirred with high-speed. The pH value was controlled at 8–9 and span-80 was added as surfactant. The mixture was stirred at 40–45 °C for 3 h. Then the mixture was filtered and washed with water and ethanol for several times and then dried. Each sample was analyzed by FT-IR and XPS. The infrared spectrum was recorded on a KBr pressed disk. The excitation and emission spectra were recorded on spectrophotometer (F-4500 FL) at room temperature. The brightness and decay time were measured with spectrometer (Konica Minolta LS-100). Spectral resolution of the spectrometers is ±2% during 0.001–0.999 cd/m2, ± 1% when N 0.999 cd/m2. 3. Results and discussion Organic compounds containing O, N, F, Cl, etc. atoms which can provide electrons can coordinate with unsaturated metal ions. Sr2+, Al3+, Eu2+ and Dy3+ ions inside the SAO-ED particles are saturated by coordinating with O2−, but these ions on the surface of SAO-ED particles are unsaturated, so they are reactive, can coordinate with organic compounds. In the present work, in order to form a firm coordinate bond, organic compounds that have two or more coordinate groups were adopted to coordinate with SAO-ED particles (CD-SAO-ED) (as Scheme 1 shows).
β-diketones [7], multi-carboxylic acids [8] and heterocyclic compounds [9] are chelating reagents and have been reported as ligands to prepare phosphors. Acetyl acetone, citric acid, tartaric acid, 1, 10-phenanthroline (phen) and 8-hydroxyquinoline were selected in the present work to coordinate with SAO-ED in ethanol at the presence of span-80 with high-speed stir. The coordination of ligands with SAOED was characterized by FT-IR spectra .The absorbance of the ligands coordinated with SAO-ED arising from carbonyl group shifted to a lower frequency than that of the corresponding free ligand (as Table 1 showed). After coordinated with metal ions, the lone electron pair of oxygen atom in C_O group or C–O transferred to the shell orbit of metal ions partly. This causes the decrease of C–O bond energy and forms the stable conjugated ring. The conjugated effect made the absorbance arising from the carbonyl group to shift to a lower frequency. As to 8-hydroxyquinoline and 1, 10-phenanthroline, the absorbance arising from C_C also shifted to a lower frequency due to a conjugated effect. The stretching vibration in the complexes is shifted to a lower frequency lower than that of the corresponding free ligand, which indicated that the coordination of these subunits to the ions occurred in the complexes. These values are in good agreement with the literature data [10]. Moreover, the presence of coordinated ligands on the surface of SAO-ED particles was confirmed by signals arising from the carbon (285 eV, C(1s-1); 287 eV, C(1s-2); 290 eV, C(1s-3)). Indeed, in the experiment the Al(2p) signals act as a marker for the SAO-ED particles and all of the C(1s) signals arise from the surface coordinated APD molecules (a small part of the signals is also from carbon of contamination). The excitation and emission spectra of SAO-ED particles coordinated with acetyl acetone, citric acid, tartaric acid, 1, 10phenanthroline (phen) and 8-hydroxyquinoline were recorded and compared with that of SAO-ED particles. The introduction of organic ligands didn't affect the luminescent properties greatly, as Figs. 1 and 2 show, and the excitation and emission spectra of the SAO-ED particle are similar with that of samples coordinated with the above ligands in peak intensity and peak shape. Each sample has only one emission peak centered at 519 nm under the excitation of 323 nm wavelength, as
Table 1 The characteristic FT-IR absorbance of free ligands and the ligands coordinated with SAO-ED Wavelength of free ligand/cm− 1 Wavelength of ligand after coordination/ cm− 1 Functional group
Citric acid
Tartaric acid
Acetyl acetone
8-hydroxyquinoline
1, 10-phenanthroline
1732 1716 Vibration of C_O
1746 1709 Vibration of C_O
1720 1680 Vibration of C_O
1507 1460 Vibration of C_C
1475 1456 Vibration of C_C
S. Wu et al. / Materials Letters 61 (2007) 3185–3188
Fig. 1. The emission spectra of SAO-ED material and SAO-ED coordinated with different ligands.
a result of the 5d to 4f transition of Eu2+ ions in SrAl2O4. This is due to the fact that the amount of Eu2+ ions coordinated with ligands is limited (ligands may coordinate with other metal ions on the surface of SAOED), which leads to the ligand-to-metal charge-transfer transition to be very weak, and the emission and excitation intensity of Eu2+ ions in SrAl2O4 is strong, so the effect of ligands on the emission and excitation is not obvious. Therefore the spectra mainly reflect the characteristic emission and excitation of Eu2+ ions in SrAl2O4. Table 2 shows the brightness of SAO-ED and SAO-ED coordinated by different ligands after excitation. We can see that the introduction of organic ligands affects the luminescence properties slightly. Especially, the brightness of phen and acetyl acetone coordinated SAO-ED particles was slightly higher than that of SAO-ED particles. This may be due to the “antenna effect”. The absorption coefficients of organic chromophores are typically orders of magnitude higher than those of rare-earth ions [11], and, when photoexcitation is accompanied by efficient exciton transfer to the rare-earth ion, this provides an efficient mechanism for sensitizing the characteristic rare-earth emission—a mechanism often called the “antenna effect” [12]. The brightness decreased when citric acid and tartaric acid were introduced, and this may be due to the hydrolysis of SAO-ED particles under acidic atmosphere. The reason for the decrease of the brightness when the 8-hydroxyquinoline was introduced is the coordination of 8-hydroxyquinoline with Al3+
3187
Fig. 2. The excitation spectra of SAO-ED material and SAO-ED coordinated with different ligands.
which destroys the crystal structure of SAO-ED, and this was proved by the decrease of the diameter of SAO-ED particles and the existence of free aluminum tris-8-hydroxyquinoline. The water resistance of organic ligands coordinated SAO-ED and unmodified SAO-ED was investigated at the same condition (2 g of samples was added into 60 ml water respectively and stirred). The Table 2 Brightness (m cd/m2) of SAO-ED and SAO-ED coordinated by different ligands after excitation SAOED 1 1009 2 622 3 451 4 351 5 289 6 243 7 212 8 185 9 166 10 147 20 74 30 48
Citric acid
Tartaric acid
Acetyl acetone
phen
8-hydro xyquinoline
886 548 400 316 257 219 190 166 148 135 67 45
801 492 356 311 251 208 178 157 140 124 58 39
1025 624 456 351 287 245 209 184 166 150 74 47
1028 624 458 353 287 248 213 184 166 152 74 47
933 571 415 324 266 222 195 169 152 137 67 44
3188
S. Wu et al. / Materials Letters 61 (2007) 3185–3188
unmodified SAO-ED hydrolyzed completely in 8 h, while organic ligands coordinated SAO-ED hydrolyzed completely in 96 h. This suggests that the introduction of organic ligands increased the water resistance of SAO-ED. The compatibility of organic ligands coordinated SAO-ED and unmodified SAO-ED was also investigated at the same condition (2 g of samples was added into 20 ml ethyl acetate respectively and stirred).
4. Conclusion In conclusion, a yellow-green (emission at about 520 nm) organic–inorganic combined long afterglow phosphor was synthesized by coordinating a ligand with SAO-ED in solvents. This method can be applied to other organic–inorganic hybrid materials and is commonly applicable to prepare organic– inorganic hybrid materials for various requirements. High brightness and long decay time that are a little higher than inorganic SAO-ED were obtained. The combined phosphor had better water resistance than that of SAO-ED and good miscibility with organic compound. Acknowledgements This work was supported by the National Nature Foundation of China (No. 20476016).
References [1] [2] [3] [4] [5] [6] [7] [8]
[9]
[10] [11] [12]
A.P. Alivisatos, Science 271 (1996) 933. S. Förster, M. Antonietti, Adv. Mater. 10 (1998) 195. L. Tracy, L. Phillips, A. Jerry, et al. [P]. 1981,US 6375864. P.D. Friederike, B. Michael, O. Joachim, et al. [P]. 2000,US 6013979. Uejima Koichi, Tachiki Hideyasu, [P]. 1997, JP09125056. Kono Akiteru, [P]. 1997, JP09003449. K. Binnemans, P. Lenaerts, K. Driesen, C. Görller-Walrand, J. Mater. Chem. 14 (2004) 191–195. [19a] F.Y. Liu, L.S. Fu, J. Wang, Z. Liu, H.R. Li, H.J. Zhang, Thin Solid Films 419 (2002) 178–182; [19b] D.W. Dong, S.C. Jiang, Y.F. Men, X.L. Ji, B.Z. Jiang, Adv. Mater. 12 (2000) 646–649. [20a] H.R. Li, J. Lin, H.J. Zhang, L.S. Fu, Q.G. Meng, S.B. Wang, Chem. Mater. 14 (2002) 3651–3655; [20b] A.C. Franville, D. Zambon, R. Mahiou, Chem. Mater. 12 (2000) 428–435; [20c] F. Embert, A. Mehdi, C. Reyé, et al., Chem. Mater. 13 (2001) 4542–4549. D.R. Cousins, F.A.J. Hart, Inorg. Nucl. Chem. 29 (1967) 1745. L.H. Sloof, A. Polman, S.I. Klink, G.A. Hebbink, L. Grave, F.C.J.M. van Veggel, D.N. Reinhoudt, J.W. Hofstraat, Opt. Mater. 14 (2000) 101. J.M. Lehn, Angew. Chem., Int. Ed. Engl. 29 (1990) 1304.