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Crystallized Zn3(VO4)2: Synthesis, characterization and optical property
Journal of Alloys and Compounds 491 (2010) 378–381
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Crystallized Zn3 (VO4 )2 : Synthesis, characterization and optical property Shibing Ni, Xinghui Wang, Guo Zhou, Feng Yang, Junming Wang, Deyan He ∗ Department of Physics, Lanzhou University, Lanzhou 730000, China
a r t i c l e
i n f o
Article history: Received 18 August 2009 Received in revised form 21 October 2009 Accepted 22 October 2009 Available online 31 October 2009 Keywords: Zinc vanadium oxide Fourier transform infrared spectra Raman spectrum X-ray photoelectron spectroscopy Photoluminescence
a b s t r a c t Well-crystallized zinc vanadium oxide Zn3 (VO4 )2 micro-particles were successfully synthesized by annealing Zn3 (OH)2 V2 O7 ·nH2 O at 600 ◦ C for 10 h in N2 atmosphere. X-ray diffraction pattern of the sample is in agreement with the standard pattern of orthorhombic Zn3 (VO4 )2 . Scanning electron microscopy (SEM) image reveals that the as-synthesized particles are about 2 m in mean diameter. The structure and composition of the as-synthesized sample were further characterized by Fourier transform infrared spectra (FTIR), Raman spectrum, and X-ray photoelectron spectroscopy (XPS). Furthermore, the photoluminescence properties of the as-synthesized Zn3 (VO4 )2 were characterized via room temperature photoluminescence (PL) measurement, which exhibit excellent visible light emission ranging from 500 to 700 nm. © 2009 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Researching the structure, physical or chemical properties of material has always been a focus in material science field. During the past few years, vanadium oxides based materials have attracted much attention due to their fascinating structures and electronic, optical, and magnetic properties, which are relevant to such diverse areas as lubrication, chemical sensor, catalysis, cathode materials in batteries, and minerals [1–6]. Stimulated by those applications, much work has been done on the synthesis and characterization of various vanadium compounds such as LiV3 O8 [7], CuV2 O6 [8], and nickel(II) hybrid vanadates [9]. Zn3 (VO4 )2 has an interesting crystal structure that is of porous framework. The lattice is assembled from layers of Zn octahedra connected by vanadate groups, which was firstly reported by Hoyos et al. [10]. With such a peculiar crystal structure, this material is a potential candidate for many promising applications in different areas. However, to the best of our knowledge, there is only a few papers about Zn3 (VO4 )2 were reported by now [10,11]. Recently, we have reported hydrothermal synthesis of Zn3 (OH)2 V2 O7 ·nH2 O [12]. As an metastable phase, Zn3 (OH)2 V2 O7 ·nH2 O can be used as an active starting material for preparing other new advanced zinc vanadium oxide. In this paper, we report a simple method to prepare Zn3 (VO4 )2 micro-particles using Zn3 (OH)2 V2 O7 ·nH2 O nanosheets as precursor. The main object of this paper is to characterize the crystal structure of Zn3 (VO4 )2 , and to research its photoluminescence properties.
All the chemicals are of analytical grade and purchased from Shanghai Chemical Reagents. 2.1. Preparation of Zn3 (OH)2 V2 O7 ·nH2 O nanosheets In a typical process, 2.5 mmol V2 O5 and 2.5 mmol hexamethylenetetramine were dissolved in 30 ml distilled water, then 1.5 mmol Zn(NO3 )2 was put into the solution. After stirring for 20 min, the obtained homogeneous yellowy suspension was transfered into a 50 ml teflonlined autoclave, distilled water was subsequently added to 80% of its capacity. The autoclave was at last sealed and placed in an oven, heated at 120 ◦ C for 24 h. The precipitate was washed with distilled water and ethanol for 4 times at 6000 rpm for 5 min. Finally the resulting products were dried in an oven at 60 ◦ C for 24 h [13]. 2.2. Preparation of Zn3 (VO4 )2 particles The as-prepared Zn3 (OH)2 V2 O7˙ nH2 O nanosheets were annealed at 600 ◦ C for 10 h in N2 atmosphere. 2.3. Characterization The morphology, structure and composition of the products were characterized by Field-emission scanning electron microscopy (FE-SEM S-4800, Hitachi) equipped with energy dispersion spectrum (EDS), X-ray powder diffraction (Rigaku RINT2400 with Cu K␣ radiation), Micro-Raman spectrometer (Jobin Yvon LabRAM HR800 UV, YGA 532 nm), Fourier transform infrared spectra (IFS 66V/S Bruker, Germany), and X-ray photoelectron spectroscopy (XPS). XPS was performed on an Escalab MKII with Mg K␣ (h = 1253.6 eV) as the exciting source at a pressure of 1.0 × 10−4 Pa and a resolution of 1.00 eV. Room temperature PL was measured on Micro-Raman spectrometer (Jobin Yvon LabRAM HR800 UV, He–Cd 325 nm).
3. Results and discussion ∗ Corresponding author. Fax: +86 931 8913554. E-mail address: [email protected] (D. He). 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.10.188
The typical X-ray diffraction pattern of the as-synthesized products was shown in Fig. 1. All diffraction peaks can be indexed
S. Ni et al. / Journal of Alloys and Compounds 491 (2010) 378–381
Fig. 3. FTIR spectrum of Zn3 (VO4 )2 .
Fig. 1. X-ray diffraction pattern of the as-synthesized products.
as the orthorhombic phase of Zn3 (VO4 )2 with end-centered lattice constants a = 0.8299 nm, b = 1.152 nm, and c = 0.6111 nm, which is in good agreement with the JCPDS, No. 34-0378. Strong and sharp peaks suggest that the as-synthesized products are wellcrystallized. The reaction during the anneal process is likely to be as follows: 600 ◦ C
Zn3 (OH)2 V2 O7 · nH2 O −→ Zn3 (VO4 )2 + (n + 1)H2 O annealing
379
(1)
Fig. 2(a) shows a low magnification SEM image of Zn3 (VO4 )2 micro-particles that prepared at 600 ◦ C for 10 h in N2 atmosphere. The mean size of those particles is about 2 m. Higher magnification SEM image was shown in Fig. 2(b), which exhibits smooth surface of the particle clearly. EDS was employed for further investigation of the composition of the sample. For EDS analysis, the sample was dispersed in ethanol and then dropped on copper sheet. Fig. 2(d) shows the EDS spectrum of the sample, whereas the corresponding SEM image was shown in Fig. 2(c). The insert
in Fig. 2(d) shows the analytical results of weight and atom ratio of the sample. V and Zn elements are clearly observed from the EDS image, whereas Cu element comes from copper substrate. The atom ratio between V and Zn element is 41.61 to 58.39, which is close to the composition of Zn3 (VO4 )2 . Different morphologies of Zn3 (VO4 )2 and Zn3 (OH)2 V2 O7˙ nH2 O indicate Zn3 (OH)2 V2 O7˙ nH2 O recrystallized during the annealing process, which was shown in expression (1). Fig. 3 is the infrared spectroscopy of the as-prepared Zn3 (VO4 )2 in the wavelength region of 300–2000 cm−1 . The vibration bands at 414 and 442 cm−1 correspond to the stretching vibration Zn–O ( − ZnO) bands [14,15], which are consistent with octahedral ZnO6 . The vibration bands at 624, 658, 791, 848, and 901 cm−1 are attributed to tetrahedral VO4 vibration modes in the network [15,16]. No water and hydroxyls vibration modes were detected owing to the high temperature annealing process, which is in accordance with expression (1).
Fig. 2. SEM images and EDS pattern of the as-synthesized products. (a) Low magnification SEM image and (b) higher magnification SEM image. (c) SEM image for EDS characterization and (d) EDS pattern.
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S. Ni et al. / Journal of Alloys and Compounds 491 (2010) 378–381
Fig. 4. Raman spectrum of Zn3 (VO4 )2 .
As shown in Fig. 4, Raman spectrum of Zn3 (VO4 )2 in the wavelength region of 150–1250 cm−1 was dominated by the peaks at 155.7, 178.6, 199.6, 223.5, 261.3, 317.9, 374.1, 394, 457.3, 632.9, 691.6, 796.8, 815.7, and 860.6 cm−1 , and these peaks are the vibration bands of Zn3 (VO4 )2 . The peaks at 155.7, 457.3, 796.8, 815.7 and 860.6 cm−1 are attributed to V–O vibration, the peaks at 261.3
and 317.9 cm−1 are caused by the symmetry-related vibration [17–19], and the peaks at 178.6, 199.6, 223.5, 374.1, 394, 632.9, and 691.6 cm−1 , come from Zn–O vibration [20]. Raman spectrum of the product is well in agreement with the crystal structure of Zn3 (VO4 )2 . As Raman peaks that affected by chemical bonds and symmetry-related vibrations are complicated, further research on the structure of Zn3 (VO4 )2 should be done to clarify the Raman spectrum. XPS measurements provide further information for the evaluation of the composition and purity of the product. The wide-scan XPS spectrum of the product was shown in Fig. 5. The C 1s binding energy in the XPS spectrum located at 289 eV, and it was standardized using C 1s as reference at 284.8 eV. All other peaks were calibrated accordingly. The two strong peaks at the Zn region of 1044.5 and 1021.4 eV are respectively assigned to Zn 2p1/2 and Zn 2p3/2 , whereas the two peaks located at 524.9 and 517.3 correspond to V 2p1/2 and V 2p3/2 , respectively. The other peak located at 530.4 eV is attributed to O 1s and it can be ascribed to O2− oxidation state bound with Zn or V in the crystal lattice. A binding energy component centered near 531.8 eV that associated with the O 1s in the hydroxide species was not detected after annealing the as-synthesized Zn3 (OH)2 V2 O7 ·nH2 O at 600 ◦ C in N2 atmosphere, which indicates the elimination of hydroxyl [21]. Fig. 6 shows the PL spectrum of Zn3 (VO4 )2 that measured at room temperature using an excitation wavelength of 325 nm. A strong visible light emission ranging from 500 to 700 nm can be
Fig. 5. XPS spectra of the as-prepared Zn3 (VO4 )2 . (a) Wide scan spectrum. (b) High-resolution spectrum for Zn 2p. (c) High-resolution spectrum for V 2p. (d) High-resolution spectrum for O 1s.
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381
from 500 to 700 nm was exhibited through room temperature PL measurement. This excellent PL behavior endows it with potential applications in optical field. Further work should be done to clarify the origin of the PL property of Zn3 (VO4 )2 . Acknowledgement We gratefully acknowledge the financial support from the Teaching and Research Award Program for Outstanding Young Teachers in High Education Institutions of MOE, China. References
Fig. 6. PL spectrum of Zn3 (VO4 )2 .
found in the PL spectrum. The green emission center located at 568 nm (2.19 eV). It has been well recognized that local defects such as atom vacancies or interstitials may induce new energy levels in the band gap [22,23]. As Zn3 (VO4 )2 was obtained by annealing Zn3 (OH)2 V2 O7˙ nH2 O at 600 ◦ C in N2 atmosphere, defects such as O vacancies, Zn vacancies, or zinc interstitials can be formed effectively. In addition, EDS result shows an atom ratio between V and Zn element of 41.61 to 58.39. It indicates the deficiency of Zn element compared with the molecular formula of Zn3 (VO4 )2 . In this work, zinc vacancies are proposed for the visible light emission [24], which is in accordance with EDS result. Further work should be done to clarify the PL behavior of Zn3 (VO4 )2 in detail. The excellent PL property of Zn3 (VO4 )2 endow it with promising application in optical field. 4. Conclusions In conclusion, Zn3 (VO4 )2 micro-particles were synthesized by annealing Zn3 (OH)2 V2 O7˙ nH2 O at 600 ◦ C in N2 atmosphere. The structure and composition of Zn3 (VO4 )2 were characterized by Raman spectrum, Fourier transform infrared spectrum and X-ray photoelectron spectroscopy. Strong visible light emission ranging
[1] E. Lugscheider, O. Knotek, K. Bobzin, S. Barwulf, Surf. Coat. Technol. 133–134 (2001) 362–368. [2] A. Rudnitskaya, D.V. Evtuguin, J.A.F. Gamelas, A. Legin, Talanta 72 (2007) 497–505. [3] F. Wang, W. Ueda, Appl. Catal., A 346 (2008) 155–163. [4] X.J. Zhu, Y.X. Liu, L.M. Geng, L.B. Chen, J. Power Sources 184 (2008) 578–582. [5] D.L. Liu, S.Y. Zhan, G. Chen, W.C. Pan, C.Z. Wang, Y.J. Wei, Mater. Lett. 62 (2008) 4210–4212. [6] J.H.T. Evans, J.A. Konnert, Am. Mineral. 63 (1978) 863–868. [7] J.Q. Xu, H.L. Zhang, T. Zhang, Q.Y. Pan, Y.H. Gui, J. Alloys Compd. 467 (2009) 327–331. [8] R. Fernández de Luis, M.K. Urtiaga, J.L. Mesa, T. Rojo, M.I. Arriortua, J. Alloys Compd. 480 (2009) 54–56. [9] J.Q. Cao, X.Y. Wang, A.P. Tang, X. Wang, Y. Wang, W. Wu, J. Alloys Compd. 479 (2009) 875–878. [10] D.A. Hoyos, A. Echavarría, C. Saldarriaga, J. Mater. Sci. 36 (2001) 5515–5518. [11] R. Umemura, H. Ogawa, A. Kan, J. Eur. Ceram. Soc. 26 (2006) 2063–2068. [12] S.B. Ni, S.M. Lin, Q.T. Pan, K. Huang, F. Yang, D.Y. He, J. Alloys Compd. 477 (2009) L1–L3. [13] S.B. Ni, G. Zhou, S.M. Lin, X.H. Wang, Q.T. Pan, F. Yang, et al., Mater. Lett. 63 (2009) 2459–2461. [14] M. Ristic, S. Music, M. Ivanda, S. Popovic, J. Alloys Compd. 397 (2005) L1–L4. [15] M. Kurzawa, A. Blonska-Tabero, Mater. Res. Bull. 37 (2002) 849–858. [16] M. Sobczyk, J. Lumin. 129 (2009) 430–433. [17] P.K.L. Au, C. Calvo, Can. J. Chem. 45 (1967) 2297–2302. [18] R. Gopal, C. Calvo, Can. J. Chem. 51 (1973) 1004–1009. [19] R. Gopal, C. Calvo, Acta. Crystallogr. 830 (1974) 2491–2493. [20] R. Zhang, P.G. Yin, N. Wang, L. Guo, Solid State Sci. 11 (2009) 865–869. [21] C.D. Wagner, D.E. Passoja, H.F. Hillery, T.G. Kinisky, H.A. Six, W.T. Jansen, J.A. Taylor, J. Vac. Sci. Technol. 21 (1982) 933–944. [22] H.B. Zeng, Z.G. Li, W.P. Cai, B.Q. Cao, P.S. Liu, S.K. Yang, J. Phys. Chem. B 111 (2007) 14311–14317. [23] H.B. Zeng, W.P. Cai, J.L. Hu, G.T. Duan, P.S. Liu, Y. Li, Appl. Phys. Lett. 88 (2006), 171910 3p. [24] B.X. Lin, Z.X. Fu, Y.B. Jia, Appl. Phys. Lett. 79 (2001) 943–945.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Crystallized Zn3 (VO4 )2 : Synthesis, characterization and optical property Shibing Ni, Xinghui Wang, Guo Zhou, Feng Yang, Junming Wang, Deyan He ∗ Department of Physics, Lanzhou University, Lanzhou 730000, China
a r t i c l e
i n f o
Article history: Received 18 August 2009 Received in revised form 21 October 2009 Accepted 22 October 2009 Available online 31 October 2009 Keywords: Zinc vanadium oxide Fourier transform infrared spectra Raman spectrum X-ray photoelectron spectroscopy Photoluminescence
a b s t r a c t Well-crystallized zinc vanadium oxide Zn3 (VO4 )2 micro-particles were successfully synthesized by annealing Zn3 (OH)2 V2 O7 ·nH2 O at 600 ◦ C for 10 h in N2 atmosphere. X-ray diffraction pattern of the sample is in agreement with the standard pattern of orthorhombic Zn3 (VO4 )2 . Scanning electron microscopy (SEM) image reveals that the as-synthesized particles are about 2 m in mean diameter. The structure and composition of the as-synthesized sample were further characterized by Fourier transform infrared spectra (FTIR), Raman spectrum, and X-ray photoelectron spectroscopy (XPS). Furthermore, the photoluminescence properties of the as-synthesized Zn3 (VO4 )2 were characterized via room temperature photoluminescence (PL) measurement, which exhibit excellent visible light emission ranging from 500 to 700 nm. © 2009 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Researching the structure, physical or chemical properties of material has always been a focus in material science field. During the past few years, vanadium oxides based materials have attracted much attention due to their fascinating structures and electronic, optical, and magnetic properties, which are relevant to such diverse areas as lubrication, chemical sensor, catalysis, cathode materials in batteries, and minerals [1–6]. Stimulated by those applications, much work has been done on the synthesis and characterization of various vanadium compounds such as LiV3 O8 [7], CuV2 O6 [8], and nickel(II) hybrid vanadates [9]. Zn3 (VO4 )2 has an interesting crystal structure that is of porous framework. The lattice is assembled from layers of Zn octahedra connected by vanadate groups, which was firstly reported by Hoyos et al. [10]. With such a peculiar crystal structure, this material is a potential candidate for many promising applications in different areas. However, to the best of our knowledge, there is only a few papers about Zn3 (VO4 )2 were reported by now [10,11]. Recently, we have reported hydrothermal synthesis of Zn3 (OH)2 V2 O7 ·nH2 O [12]. As an metastable phase, Zn3 (OH)2 V2 O7 ·nH2 O can be used as an active starting material for preparing other new advanced zinc vanadium oxide. In this paper, we report a simple method to prepare Zn3 (VO4 )2 micro-particles using Zn3 (OH)2 V2 O7 ·nH2 O nanosheets as precursor. The main object of this paper is to characterize the crystal structure of Zn3 (VO4 )2 , and to research its photoluminescence properties.
All the chemicals are of analytical grade and purchased from Shanghai Chemical Reagents. 2.1. Preparation of Zn3 (OH)2 V2 O7 ·nH2 O nanosheets In a typical process, 2.5 mmol V2 O5 and 2.5 mmol hexamethylenetetramine were dissolved in 30 ml distilled water, then 1.5 mmol Zn(NO3 )2 was put into the solution. After stirring for 20 min, the obtained homogeneous yellowy suspension was transfered into a 50 ml teflonlined autoclave, distilled water was subsequently added to 80% of its capacity. The autoclave was at last sealed and placed in an oven, heated at 120 ◦ C for 24 h. The precipitate was washed with distilled water and ethanol for 4 times at 6000 rpm for 5 min. Finally the resulting products were dried in an oven at 60 ◦ C for 24 h [13]. 2.2. Preparation of Zn3 (VO4 )2 particles The as-prepared Zn3 (OH)2 V2 O7˙ nH2 O nanosheets were annealed at 600 ◦ C for 10 h in N2 atmosphere. 2.3. Characterization The morphology, structure and composition of the products were characterized by Field-emission scanning electron microscopy (FE-SEM S-4800, Hitachi) equipped with energy dispersion spectrum (EDS), X-ray powder diffraction (Rigaku RINT2400 with Cu K␣ radiation), Micro-Raman spectrometer (Jobin Yvon LabRAM HR800 UV, YGA 532 nm), Fourier transform infrared spectra (IFS 66V/S Bruker, Germany), and X-ray photoelectron spectroscopy (XPS). XPS was performed on an Escalab MKII with Mg K␣ (h = 1253.6 eV) as the exciting source at a pressure of 1.0 × 10−4 Pa and a resolution of 1.00 eV. Room temperature PL was measured on Micro-Raman spectrometer (Jobin Yvon LabRAM HR800 UV, He–Cd 325 nm).
3. Results and discussion ∗ Corresponding author. Fax: +86 931 8913554. E-mail address: [email protected] (D. He). 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.10.188
The typical X-ray diffraction pattern of the as-synthesized products was shown in Fig. 1. All diffraction peaks can be indexed
S. Ni et al. / Journal of Alloys and Compounds 491 (2010) 378–381
Fig. 3. FTIR spectrum of Zn3 (VO4 )2 .
Fig. 1. X-ray diffraction pattern of the as-synthesized products.
as the orthorhombic phase of Zn3 (VO4 )2 with end-centered lattice constants a = 0.8299 nm, b = 1.152 nm, and c = 0.6111 nm, which is in good agreement with the JCPDS, No. 34-0378. Strong and sharp peaks suggest that the as-synthesized products are wellcrystallized. The reaction during the anneal process is likely to be as follows: 600 ◦ C
Zn3 (OH)2 V2 O7 · nH2 O −→ Zn3 (VO4 )2 + (n + 1)H2 O annealing
379
(1)
Fig. 2(a) shows a low magnification SEM image of Zn3 (VO4 )2 micro-particles that prepared at 600 ◦ C for 10 h in N2 atmosphere. The mean size of those particles is about 2 m. Higher magnification SEM image was shown in Fig. 2(b), which exhibits smooth surface of the particle clearly. EDS was employed for further investigation of the composition of the sample. For EDS analysis, the sample was dispersed in ethanol and then dropped on copper sheet. Fig. 2(d) shows the EDS spectrum of the sample, whereas the corresponding SEM image was shown in Fig. 2(c). The insert
in Fig. 2(d) shows the analytical results of weight and atom ratio of the sample. V and Zn elements are clearly observed from the EDS image, whereas Cu element comes from copper substrate. The atom ratio between V and Zn element is 41.61 to 58.39, which is close to the composition of Zn3 (VO4 )2 . Different morphologies of Zn3 (VO4 )2 and Zn3 (OH)2 V2 O7˙ nH2 O indicate Zn3 (OH)2 V2 O7˙ nH2 O recrystallized during the annealing process, which was shown in expression (1). Fig. 3 is the infrared spectroscopy of the as-prepared Zn3 (VO4 )2 in the wavelength region of 300–2000 cm−1 . The vibration bands at 414 and 442 cm−1 correspond to the stretching vibration Zn–O ( − ZnO) bands [14,15], which are consistent with octahedral ZnO6 . The vibration bands at 624, 658, 791, 848, and 901 cm−1 are attributed to tetrahedral VO4 vibration modes in the network [15,16]. No water and hydroxyls vibration modes were detected owing to the high temperature annealing process, which is in accordance with expression (1).
Fig. 2. SEM images and EDS pattern of the as-synthesized products. (a) Low magnification SEM image and (b) higher magnification SEM image. (c) SEM image for EDS characterization and (d) EDS pattern.
380
S. Ni et al. / Journal of Alloys and Compounds 491 (2010) 378–381
Fig. 4. Raman spectrum of Zn3 (VO4 )2 .
As shown in Fig. 4, Raman spectrum of Zn3 (VO4 )2 in the wavelength region of 150–1250 cm−1 was dominated by the peaks at 155.7, 178.6, 199.6, 223.5, 261.3, 317.9, 374.1, 394, 457.3, 632.9, 691.6, 796.8, 815.7, and 860.6 cm−1 , and these peaks are the vibration bands of Zn3 (VO4 )2 . The peaks at 155.7, 457.3, 796.8, 815.7 and 860.6 cm−1 are attributed to V–O vibration, the peaks at 261.3
and 317.9 cm−1 are caused by the symmetry-related vibration [17–19], and the peaks at 178.6, 199.6, 223.5, 374.1, 394, 632.9, and 691.6 cm−1 , come from Zn–O vibration [20]. Raman spectrum of the product is well in agreement with the crystal structure of Zn3 (VO4 )2 . As Raman peaks that affected by chemical bonds and symmetry-related vibrations are complicated, further research on the structure of Zn3 (VO4 )2 should be done to clarify the Raman spectrum. XPS measurements provide further information for the evaluation of the composition and purity of the product. The wide-scan XPS spectrum of the product was shown in Fig. 5. The C 1s binding energy in the XPS spectrum located at 289 eV, and it was standardized using C 1s as reference at 284.8 eV. All other peaks were calibrated accordingly. The two strong peaks at the Zn region of 1044.5 and 1021.4 eV are respectively assigned to Zn 2p1/2 and Zn 2p3/2 , whereas the two peaks located at 524.9 and 517.3 correspond to V 2p1/2 and V 2p3/2 , respectively. The other peak located at 530.4 eV is attributed to O 1s and it can be ascribed to O2− oxidation state bound with Zn or V in the crystal lattice. A binding energy component centered near 531.8 eV that associated with the O 1s in the hydroxide species was not detected after annealing the as-synthesized Zn3 (OH)2 V2 O7 ·nH2 O at 600 ◦ C in N2 atmosphere, which indicates the elimination of hydroxyl [21]. Fig. 6 shows the PL spectrum of Zn3 (VO4 )2 that measured at room temperature using an excitation wavelength of 325 nm. A strong visible light emission ranging from 500 to 700 nm can be
Fig. 5. XPS spectra of the as-prepared Zn3 (VO4 )2 . (a) Wide scan spectrum. (b) High-resolution spectrum for Zn 2p. (c) High-resolution spectrum for V 2p. (d) High-resolution spectrum for O 1s.
S. Ni et al. / Journal of Alloys and Compounds 491 (2010) 378–381
381
from 500 to 700 nm was exhibited through room temperature PL measurement. This excellent PL behavior endows it with potential applications in optical field. Further work should be done to clarify the origin of the PL property of Zn3 (VO4 )2 . Acknowledgement We gratefully acknowledge the financial support from the Teaching and Research Award Program for Outstanding Young Teachers in High Education Institutions of MOE, China. References
Fig. 6. PL spectrum of Zn3 (VO4 )2 .
found in the PL spectrum. The green emission center located at 568 nm (2.19 eV). It has been well recognized that local defects such as atom vacancies or interstitials may induce new energy levels in the band gap [22,23]. As Zn3 (VO4 )2 was obtained by annealing Zn3 (OH)2 V2 O7˙ nH2 O at 600 ◦ C in N2 atmosphere, defects such as O vacancies, Zn vacancies, or zinc interstitials can be formed effectively. In addition, EDS result shows an atom ratio between V and Zn element of 41.61 to 58.39. It indicates the deficiency of Zn element compared with the molecular formula of Zn3 (VO4 )2 . In this work, zinc vacancies are proposed for the visible light emission [24], which is in accordance with EDS result. Further work should be done to clarify the PL behavior of Zn3 (VO4 )2 in detail. The excellent PL property of Zn3 (VO4 )2 endow it with promising application in optical field. 4. Conclusions In conclusion, Zn3 (VO4 )2 micro-particles were synthesized by annealing Zn3 (OH)2 V2 O7˙ nH2 O at 600 ◦ C in N2 atmosphere. The structure and composition of Zn3 (VO4 )2 were characterized by Raman spectrum, Fourier transform infrared spectrum and X-ray photoelectron spectroscopy. Strong visible light emission ranging
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