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Preparation of Eu-doped LaPO4 films using successive-ionic-layer-adsorption-and-reaction
Materials Letters 64 (2010) 1861–1864
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Preparation of Eu-doped LaPO4 films using successive-ionic-layer-adsorption-and-reaction Sangmoon Park a, Zhao Zhen b, Dong Ho Park b,⁎ a b
Center for Green Fusion Technology & Department of Engineering in Energy and Applied Chemistry, Silla University, Busan 617-736, Republic of Korea Department of Biomedicinal Chemistry, Institute of Basic Science, Inje University, 607 Gimhae, Gyungnam 621-749, Republic of Korea
a r t i c l e
i n f o
Article history: Received 22 March 2010 Accepted 13 May 2010 Available online 21 May 2010 Keywords: Thin films Phosphors Eu-doping Lanthanum orthophosphate SILAR Nanofiber
a b s t r a c t Thin films of Eu-doped lanthanum orthophosphate (LaPO4) were fabricated on glass substrates using the successive-ionic-layer-adsorption-and-reaction method and subsequent hydrothermal and furnace annealing. A monoclinic structure was observed to be present in LaPO4:Eu films after hydrothermal annealing at 200 °C. Scanning electron microscopy and transmission electron microscopy images of LaPO4:Eu films show the homogenously close-packed morphology of micro-sized nanofibers at around 10 to 20 nm in diameter. The red emission activated at 254 nm was obtained from LaPO4:Eu films. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Lanthanide orthophosphates (LnPO4) have been used in various applications including sensors, proton conductors for fuel cells, catalysts, heat-resistant materials, and scintillators [1–4]. Lanthanum orthophosphates (LaPO4) is a well known host material for a highly efficient phosphor in modern display fields such as plasma display panel and field emission display. Fabrication of LaPO4 films could be achieved as a result of several coating techniques, layerby-layer (LbL) assembly method [5], spin coating [6], electrospinning [7], ink-jet printing [8], ultrasonic mechanical coating and armouring (UMCA) [9], and sol–gel process combined with soft lithography [10]. Since 2002 the combination of hydrothermal dehydration and crystallization process with successive-ioniclayer-adsorption-and-reaction (SILAR) has been introduced as a simple and general technique for thin-film deposition and crystallization of metal oxides, for instance ZrO2 [11], TiO2 [12], and iron oxides [13]. Among the aforementioned thin-film fabrication methods, LbL method is known to be quite similar to SILAR technique. Both SILAR and LbL processes can be performed in solutions carrying a given substrate alternatively in contact with cation and anion agents. The prominent difference is that nanoparticles can be consecutively created during the SILAR deposition process, while LbL assembly can be executed using
⁎ Corresponding author. Tel.: + 82 55 320 3224; fax: + 82 55 321 9718. E-mail address: [email protected] (D.H. Park). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.05.017
already-synthesized nanoparticles with charged polyelectrolytes in a previous step. The present study reports on the fabrication of LaPO4:Eu films using the SILAR method followed by hydrothermal and furnace annealing. The phase of obtained thin films was characterized by means of X-ray diffraction (XRD). Their morphology was acquired by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photoluminescent property of Eu-doped LaPO4 films was also investigated. 2. Experimental 2.1. Preparation of LaPO4:Eu thin film by SILAR method All chemical reagents were of analytical grade. The cationic precursor for LaPO4:Eu was a mixed aqueous solution of La (NO3)3·6H2O and Eu(NO3)3·6H2O with pH = 8.5. The molarity of La (III) and Eu(III) in cationic precursor solution was 0.004 M and 0.001 M, respectively. The anionic precursor was 0.005 M-Na2HPO4 aqueous solution with pH = 9.4 [14]. Pre-cleaned glass substrates were immersed in the cationic precursor solution for 1 s, which lead La(III) and Eu(III) to be electrostatically adsorbed on the surface. The cation-adsorbed substrate was immersed in a rinsing vessel of doubly deionized water agitated by stirring bar for 10 s to remove the excess in ionic species except for the cationic monolayer adsorbed to SiO− moieties on the surface. This resultant substrate was then immersed in the anionic precursor solution for 1 s. Phosphate ions reacted with the adsorbed La or Eu cations on the glass substrate. The substrate was then rinsed in the water vessel for 10 s to remove the excess in ionic
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with an operating voltage of 200 kV using LaB6 filament electron gun. Samples for TEM were obtained by dispersing the films in ethanol via ultrasonication for 1 h, and by dropping a few drops of the resultant suspension onto a copper grid pre-coated with amorphous carbon and allowing them to dry naturally. The emission spectra were obtained at room temperature using Shimadzu RF-5300PC fluorometer with a xenon flash lamp. 3. Results and discussions 3.1. Phase transform of Eu: LaPO4 film
Fig. 1. X-ray diffraction patterns of (a) calculated LaPO4 (ICSD 79747), (b) glass substrate, LaPO4:Eu film (c) dried at 100 °C, (d) annealed hydrothermally at 200 °C, and (e) annealed in furnace at 500 °C after hydrothermal treatment at 200 °C.
species except for La(Eu)PO4 ionic pairs. The ratio of La vs. Eu in LaPO4:Eu thin films was 3.5:1.0, as indicated by the energy dispersive spectrometer (EDS) result. As-prepared LaPO4:Eu films obtained from 700 SILAR cycles were dried at 100 °C. LaPO4:Eu films were generated by hydrothermal annealing using Teflon-lined autoclave at 200 °C for 2 h and subsequent annealing at 500 °C in a furnace. 2.2. Sample characterization The morphology and thickness of films were investigated by SEM (Hitachi S-4300). The formation of a single phase of films was confirmed by X-ray diffraction with CuKα radiation using Shimadzu XRD-6000. TEM images were taken by JEOL JEM-2010 microscope
LaPO4 crystal structures consist of the hexagonal (space group P6222) and monoclinic (space group P21/n) which are low-temperature and high-temperature phases, respectively. Their irreversible transformation initiates by thermal treatment at 600 °C in air; however the monoclinic structure could be obtained at quite a low temperature (200 °C) using hydrothermal annealing method [15]. The as-prepared LaPO4 films were hydrothermally annealed at 200 °C and subsequently heated at 500 °C in air. All films were characterized by X-ray powder diffraction measurements to identify LaPO4 phases present. The ICSD data (number 79747) of monoclinic LaPO4 were used to index the observed LaPO4 phases, as shown in Fig. 1(a). The broad substrate peak on glass was observed at around 2θ = 20–30° (Fig. 1(b)). The two asterisked peaks around 2θ = 20–30° were barely observed in the XRD pattern for as-made films (Fig. 1(c)), which were dried at 100 °C in air. The two asterisked peaks correspond to the two strong (110) and (200) peaks of hexagonal LaPO4 phase which is the low-temperature structure [14]. When the films were hydrothermally annealed at 200 °C, the (200)/(120) and (012) monoclinic LaPO4 peaks around 2θ = ∼ 29 and 31° were attained in Fig. 1(d) [16]. As for the film obtained from hydrothermal annealing at 200 °C and subsequent annealing at 500 °C, XRD peaks were sharpened with remaining the monoclinic phase.
Fig. 2. SEM images of LaPO4:Eu films : (a) top view and (b) side view obtained from 0.005 M precursor solutions and (c) side view obtained from 0.001 M precursor solutions.
S. Park et al. / Materials Letters 64 (2010) 1861–1864
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Fig. 3. TEM image of LaPO4:Eu nanofibers (a) dried at 100 °C (b) annealed hydrothermally at 200 °C and (c) annealed in furnace at 500 °C after hydrothermal treatment at 200 °C.
3.2. Morphology of LaPO4:Eu films
3.3. TEM images of LaPO4:Eu nanofibers
Fig. 2 exhibits SEM images of LaPO4:Eu film on a glass substrate. The top view of the film illustrates a homogeneous flat surface with covering the substrate well. As shown in the magnified SEM image (Fig. 2(a)), the film consists of nanofibers parallel to the substrate surface. Nanofibers of LaPO4:Tb phosphors on a substrate were reported by How et al. using the method of sol–gel process and electrospinning with high-voltage supply at 18 kV [7]. The stepwise accumulation of nanofiber through the controlled deposition of Eudoped lanthanum phosphate via SILAR method also occurred. The same close-packed morphology of films obtained from the precursor solutions with different concentrations (0.05 and 0.01 M) as well as as-prepared and annealed films was also an accumulated nanofiber. In order to investigate the depth profile of film, LaPO4:Eu film was cut and its cross-section was monitored by SEM (Fig. 2(b)). The diameter of nanofibers is ranged from 10 nm to 20 nm. The magnified SEM image of the cross-section of film consists of circles with diameters of ∼ 10 nm to ∼ 20 nm from bottom to top. These circles are the crosssections of the nanofibers parallel to the substrate surface. The thickness of film was ∼ 9.2 μm, which is proportional to the concentration of precursor solutions. On the other hand, the thickness of film obtained from the precursor solutions of 0.001 M was ∼ 2.0 μm (Fig. 2(c)).
Fig. 3(a) shows the TEM image of LaPO4:Eu nanofibers dried at 100 °C, which provide the morphologies of one-dimensional LaPO4:Eu nanofibers. The nanofibers annealed hydrothermally at 200 °C were composed of close-linked nanoparticles (Fig. 3(b)), likewise the nanofibers prepared by sol–gel and electrospinning process [7]. The parallel lattice fringes with regular interplanar distance of 0.31 nm in the LaPO4:Eu nanofibers were resulted from the formation of the crystalline nanofibers of monoclinic phase. The TEM of LaPO4:Eu nanofibers annealed in the furnace at 500 °C after hydrothermal treatment at 200 °C shows similar lattice fringes with that of nanofibers annealed hydrothermally at 200 °C due to their same monoclinic structure (Fig. 3(c)). 3.4. Photoluminescent property of LaPO4:Eu films Fig. 4 shows the photoluminescence spectra of the La1 − xEuxPO4 (x = 0.2, 0.4) films fabricated by SILAR and subsequent hydrothermal (200 °C) and furnace (500 °C) annealing. The major red emission peak of Eu-activated LaPO4 using the excitation line at 254 nm corresponds to the 5D0–7F1 (magnetic dipole) and 5D0–7F2 (electric dipole) transitions of Eu3+ located at 592 and 619 nm, respectively. It is known that as Eu3+ ions occupy inversion center sites in LaPO4, so the 5D0–7F1 magnetic dipole transition was relatively strong as compared to the 5D0–7F2 electric dipole transition [16]. These emission lines of Eu-doped LaPO4 in Fig. 4 are in good agreement with other reports [16,17]. The inset in Fig. 4 shows the photo of red emission of Eu-doped LaPO4 on glass substrate under a 254 nm UV lamp. 4. Conclusions La,Eu(NO3)3·6H2O and Na2HPO4 were used as precursors to fabricate LaPO4:Eu films using the SILAR method. Based on XRD results, monoclinic phase of LaPO4:Eu was identified. SEM and TEM images revealed homogenously quite long nanofibers with diameters of around 10 to 20 nm with various film thicknesses of 2.0 and 9.2 nm. Upon excitation using 254 nm radiation, the LaPO4:Eu phosphors clearly showed 5D0–7F1 and 5D0–7F2 emission lines of Eu3+. Acknowledgement Prof. D. H. Park and Z. Zhen thank for supporting the grant from Inje University (2008). References
Fig. 4. Emission spectra and photo of red LaPO4:Eu phosphors. The inset is optical image of the red phosphors under UV irradiation.
[1] Fang Y-P, Xu A-W, Song R-Q, Zhang H-X, You L-P, Yu JC, et al. J Am Chem Soc 2003;125:16025–34.
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[2] Nishihama S, Hirai T, Komasawa I. J Mater Chem 2002;12:1053–7. [3] Onoda H, Nariai H, Moriwaki A, Maki H, Motooka I. J Mater Chem 2002;12: 1754–60. [4] Ordonez-Regil E, Drot R, Simoni E, Ehrhardt J. Langmuir 2002;18:7977–84. [5] Schuetz P, Caruso F. Chem Mater 2002;14:4509–16. [6] Jung H-K, Oh J-S, Seok S-I, Lee T-H. J Lumin 2005;114:307–13. [7] Hou Z, Wang L, Lian H, Chai R, Zhang C, Cheng Z, et al. J Solid State Chem 2009;182: 698–708. [8] Bühler G, Feldmann C. Appl Phys A 2007;87:631–6. [9] Komarov SV, Romankov SE, Son SH, Hayashi N, Kaloshkin SD, Ueno S, et al. Sur Coat Technol 2008;202:5180–4.
[10] Yu M, Lin J, Fu J, Zhang HJ, Han YC. J Mater Chem 2003;13:1413–9. [11] Park S, Clark BL, Keszler DA, Bender JP, Wager JF, Reynolds TA, et al. Science 2002;297:65. [12] Park S, DiMasi E, Kim Y-I, Han W, Woodward PM, Vogt T. Thin Solid Films 2006;515 1250-4. [13] Park SJ. Solid State Chem 2009;182:2456–60. [14] Yu J-G, Yu H-G, Cheng B, Zhao X-J, Yu JC, Ho W-K. J Phys Chem B 2003;107: 13871–9. [15] Ferhi M, Horchani-Naifer K, Ferid M. J Lumin 2008;128:1777–82. [16] Ma L, Xu L-M, Chen W-X, Xu Z-D. Mater Lett 2009;63:1635–7. [17] Yang P, Quan Z, Li C, Hou Z, Wang W, Lin J. J Solid State Chem 2009;182:1045–54.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Preparation of Eu-doped LaPO4 films using successive-ionic-layer-adsorption-and-reaction Sangmoon Park a, Zhao Zhen b, Dong Ho Park b,⁎ a b
Center for Green Fusion Technology & Department of Engineering in Energy and Applied Chemistry, Silla University, Busan 617-736, Republic of Korea Department of Biomedicinal Chemistry, Institute of Basic Science, Inje University, 607 Gimhae, Gyungnam 621-749, Republic of Korea
a r t i c l e
i n f o
Article history: Received 22 March 2010 Accepted 13 May 2010 Available online 21 May 2010 Keywords: Thin films Phosphors Eu-doping Lanthanum orthophosphate SILAR Nanofiber
a b s t r a c t Thin films of Eu-doped lanthanum orthophosphate (LaPO4) were fabricated on glass substrates using the successive-ionic-layer-adsorption-and-reaction method and subsequent hydrothermal and furnace annealing. A monoclinic structure was observed to be present in LaPO4:Eu films after hydrothermal annealing at 200 °C. Scanning electron microscopy and transmission electron microscopy images of LaPO4:Eu films show the homogenously close-packed morphology of micro-sized nanofibers at around 10 to 20 nm in diameter. The red emission activated at 254 nm was obtained from LaPO4:Eu films. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Lanthanide orthophosphates (LnPO4) have been used in various applications including sensors, proton conductors for fuel cells, catalysts, heat-resistant materials, and scintillators [1–4]. Lanthanum orthophosphates (LaPO4) is a well known host material for a highly efficient phosphor in modern display fields such as plasma display panel and field emission display. Fabrication of LaPO4 films could be achieved as a result of several coating techniques, layerby-layer (LbL) assembly method [5], spin coating [6], electrospinning [7], ink-jet printing [8], ultrasonic mechanical coating and armouring (UMCA) [9], and sol–gel process combined with soft lithography [10]. Since 2002 the combination of hydrothermal dehydration and crystallization process with successive-ioniclayer-adsorption-and-reaction (SILAR) has been introduced as a simple and general technique for thin-film deposition and crystallization of metal oxides, for instance ZrO2 [11], TiO2 [12], and iron oxides [13]. Among the aforementioned thin-film fabrication methods, LbL method is known to be quite similar to SILAR technique. Both SILAR and LbL processes can be performed in solutions carrying a given substrate alternatively in contact with cation and anion agents. The prominent difference is that nanoparticles can be consecutively created during the SILAR deposition process, while LbL assembly can be executed using
⁎ Corresponding author. Tel.: + 82 55 320 3224; fax: + 82 55 321 9718. E-mail address: [email protected] (D.H. Park). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.05.017
already-synthesized nanoparticles with charged polyelectrolytes in a previous step. The present study reports on the fabrication of LaPO4:Eu films using the SILAR method followed by hydrothermal and furnace annealing. The phase of obtained thin films was characterized by means of X-ray diffraction (XRD). Their morphology was acquired by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photoluminescent property of Eu-doped LaPO4 films was also investigated. 2. Experimental 2.1. Preparation of LaPO4:Eu thin film by SILAR method All chemical reagents were of analytical grade. The cationic precursor for LaPO4:Eu was a mixed aqueous solution of La (NO3)3·6H2O and Eu(NO3)3·6H2O with pH = 8.5. The molarity of La (III) and Eu(III) in cationic precursor solution was 0.004 M and 0.001 M, respectively. The anionic precursor was 0.005 M-Na2HPO4 aqueous solution with pH = 9.4 [14]. Pre-cleaned glass substrates were immersed in the cationic precursor solution for 1 s, which lead La(III) and Eu(III) to be electrostatically adsorbed on the surface. The cation-adsorbed substrate was immersed in a rinsing vessel of doubly deionized water agitated by stirring bar for 10 s to remove the excess in ionic species except for the cationic monolayer adsorbed to SiO− moieties on the surface. This resultant substrate was then immersed in the anionic precursor solution for 1 s. Phosphate ions reacted with the adsorbed La or Eu cations on the glass substrate. The substrate was then rinsed in the water vessel for 10 s to remove the excess in ionic
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with an operating voltage of 200 kV using LaB6 filament electron gun. Samples for TEM were obtained by dispersing the films in ethanol via ultrasonication for 1 h, and by dropping a few drops of the resultant suspension onto a copper grid pre-coated with amorphous carbon and allowing them to dry naturally. The emission spectra were obtained at room temperature using Shimadzu RF-5300PC fluorometer with a xenon flash lamp. 3. Results and discussions 3.1. Phase transform of Eu: LaPO4 film
Fig. 1. X-ray diffraction patterns of (a) calculated LaPO4 (ICSD 79747), (b) glass substrate, LaPO4:Eu film (c) dried at 100 °C, (d) annealed hydrothermally at 200 °C, and (e) annealed in furnace at 500 °C after hydrothermal treatment at 200 °C.
species except for La(Eu)PO4 ionic pairs. The ratio of La vs. Eu in LaPO4:Eu thin films was 3.5:1.0, as indicated by the energy dispersive spectrometer (EDS) result. As-prepared LaPO4:Eu films obtained from 700 SILAR cycles were dried at 100 °C. LaPO4:Eu films were generated by hydrothermal annealing using Teflon-lined autoclave at 200 °C for 2 h and subsequent annealing at 500 °C in a furnace. 2.2. Sample characterization The morphology and thickness of films were investigated by SEM (Hitachi S-4300). The formation of a single phase of films was confirmed by X-ray diffraction with CuKα radiation using Shimadzu XRD-6000. TEM images were taken by JEOL JEM-2010 microscope
LaPO4 crystal structures consist of the hexagonal (space group P6222) and monoclinic (space group P21/n) which are low-temperature and high-temperature phases, respectively. Their irreversible transformation initiates by thermal treatment at 600 °C in air; however the monoclinic structure could be obtained at quite a low temperature (200 °C) using hydrothermal annealing method [15]. The as-prepared LaPO4 films were hydrothermally annealed at 200 °C and subsequently heated at 500 °C in air. All films were characterized by X-ray powder diffraction measurements to identify LaPO4 phases present. The ICSD data (number 79747) of monoclinic LaPO4 were used to index the observed LaPO4 phases, as shown in Fig. 1(a). The broad substrate peak on glass was observed at around 2θ = 20–30° (Fig. 1(b)). The two asterisked peaks around 2θ = 20–30° were barely observed in the XRD pattern for as-made films (Fig. 1(c)), which were dried at 100 °C in air. The two asterisked peaks correspond to the two strong (110) and (200) peaks of hexagonal LaPO4 phase which is the low-temperature structure [14]. When the films were hydrothermally annealed at 200 °C, the (200)/(120) and (012) monoclinic LaPO4 peaks around 2θ = ∼ 29 and 31° were attained in Fig. 1(d) [16]. As for the film obtained from hydrothermal annealing at 200 °C and subsequent annealing at 500 °C, XRD peaks were sharpened with remaining the monoclinic phase.
Fig. 2. SEM images of LaPO4:Eu films : (a) top view and (b) side view obtained from 0.005 M precursor solutions and (c) side view obtained from 0.001 M precursor solutions.
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Fig. 3. TEM image of LaPO4:Eu nanofibers (a) dried at 100 °C (b) annealed hydrothermally at 200 °C and (c) annealed in furnace at 500 °C after hydrothermal treatment at 200 °C.
3.2. Morphology of LaPO4:Eu films
3.3. TEM images of LaPO4:Eu nanofibers
Fig. 2 exhibits SEM images of LaPO4:Eu film on a glass substrate. The top view of the film illustrates a homogeneous flat surface with covering the substrate well. As shown in the magnified SEM image (Fig. 2(a)), the film consists of nanofibers parallel to the substrate surface. Nanofibers of LaPO4:Tb phosphors on a substrate were reported by How et al. using the method of sol–gel process and electrospinning with high-voltage supply at 18 kV [7]. The stepwise accumulation of nanofiber through the controlled deposition of Eudoped lanthanum phosphate via SILAR method also occurred. The same close-packed morphology of films obtained from the precursor solutions with different concentrations (0.05 and 0.01 M) as well as as-prepared and annealed films was also an accumulated nanofiber. In order to investigate the depth profile of film, LaPO4:Eu film was cut and its cross-section was monitored by SEM (Fig. 2(b)). The diameter of nanofibers is ranged from 10 nm to 20 nm. The magnified SEM image of the cross-section of film consists of circles with diameters of ∼ 10 nm to ∼ 20 nm from bottom to top. These circles are the crosssections of the nanofibers parallel to the substrate surface. The thickness of film was ∼ 9.2 μm, which is proportional to the concentration of precursor solutions. On the other hand, the thickness of film obtained from the precursor solutions of 0.001 M was ∼ 2.0 μm (Fig. 2(c)).
Fig. 3(a) shows the TEM image of LaPO4:Eu nanofibers dried at 100 °C, which provide the morphologies of one-dimensional LaPO4:Eu nanofibers. The nanofibers annealed hydrothermally at 200 °C were composed of close-linked nanoparticles (Fig. 3(b)), likewise the nanofibers prepared by sol–gel and electrospinning process [7]. The parallel lattice fringes with regular interplanar distance of 0.31 nm in the LaPO4:Eu nanofibers were resulted from the formation of the crystalline nanofibers of monoclinic phase. The TEM of LaPO4:Eu nanofibers annealed in the furnace at 500 °C after hydrothermal treatment at 200 °C shows similar lattice fringes with that of nanofibers annealed hydrothermally at 200 °C due to their same monoclinic structure (Fig. 3(c)). 3.4. Photoluminescent property of LaPO4:Eu films Fig. 4 shows the photoluminescence spectra of the La1 − xEuxPO4 (x = 0.2, 0.4) films fabricated by SILAR and subsequent hydrothermal (200 °C) and furnace (500 °C) annealing. The major red emission peak of Eu-activated LaPO4 using the excitation line at 254 nm corresponds to the 5D0–7F1 (magnetic dipole) and 5D0–7F2 (electric dipole) transitions of Eu3+ located at 592 and 619 nm, respectively. It is known that as Eu3+ ions occupy inversion center sites in LaPO4, so the 5D0–7F1 magnetic dipole transition was relatively strong as compared to the 5D0–7F2 electric dipole transition [16]. These emission lines of Eu-doped LaPO4 in Fig. 4 are in good agreement with other reports [16,17]. The inset in Fig. 4 shows the photo of red emission of Eu-doped LaPO4 on glass substrate under a 254 nm UV lamp. 4. Conclusions La,Eu(NO3)3·6H2O and Na2HPO4 were used as precursors to fabricate LaPO4:Eu films using the SILAR method. Based on XRD results, monoclinic phase of LaPO4:Eu was identified. SEM and TEM images revealed homogenously quite long nanofibers with diameters of around 10 to 20 nm with various film thicknesses of 2.0 and 9.2 nm. Upon excitation using 254 nm radiation, the LaPO4:Eu phosphors clearly showed 5D0–7F1 and 5D0–7F2 emission lines of Eu3+. Acknowledgement Prof. D. H. Park and Z. Zhen thank for supporting the grant from Inje University (2008). References
Fig. 4. Emission spectra and photo of red LaPO4:Eu phosphors. The inset is optical image of the red phosphors under UV irradiation.
[1] Fang Y-P, Xu A-W, Song R-Q, Zhang H-X, You L-P, Yu JC, et al. J Am Chem Soc 2003;125:16025–34.
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S. Park et al. / Materials Letters 64 (2010) 1861–1864
[2] Nishihama S, Hirai T, Komasawa I. J Mater Chem 2002;12:1053–7. [3] Onoda H, Nariai H, Moriwaki A, Maki H, Motooka I. J Mater Chem 2002;12: 1754–60. [4] Ordonez-Regil E, Drot R, Simoni E, Ehrhardt J. Langmuir 2002;18:7977–84. [5] Schuetz P, Caruso F. Chem Mater 2002;14:4509–16. [6] Jung H-K, Oh J-S, Seok S-I, Lee T-H. J Lumin 2005;114:307–13. [7] Hou Z, Wang L, Lian H, Chai R, Zhang C, Cheng Z, et al. J Solid State Chem 2009;182: 698–708. [8] Bühler G, Feldmann C. Appl Phys A 2007;87:631–6. [9] Komarov SV, Romankov SE, Son SH, Hayashi N, Kaloshkin SD, Ueno S, et al. Sur Coat Technol 2008;202:5180–4.
[10] Yu M, Lin J, Fu J, Zhang HJ, Han YC. J Mater Chem 2003;13:1413–9. [11] Park S, Clark BL, Keszler DA, Bender JP, Wager JF, Reynolds TA, et al. Science 2002;297:65. [12] Park S, DiMasi E, Kim Y-I, Han W, Woodward PM, Vogt T. Thin Solid Films 2006;515 1250-4. [13] Park SJ. Solid State Chem 2009;182:2456–60. [14] Yu J-G, Yu H-G, Cheng B, Zhao X-J, Yu JC, Ho W-K. J Phys Chem B 2003;107: 13871–9. [15] Ferhi M, Horchani-Naifer K, Ferid M. J Lumin 2008;128:1777–82. [16] Ma L, Xu L-M, Chen W-X, Xu Z-D. Mater Lett 2009;63:1635–7. [17] Yang P, Quan Z, Li C, Hou Z, Wang W, Lin J. J Solid State Chem 2009;182:1045–54.