In this work, CaWO4 nanoparticles have been synthesized by microwave-assisted method at a low temperature of 120°C. The as-prepared powders were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). It is found that the reaction time played an important role in the morphology controlling and crystallinity level of CaWO4 crystals. The effects of photoluminescent properties have a great relationship with crystallinity. 1. Introduction In recent years, with the advance of nanoscale materials science and technology, the synthesis of nanoscale materials with unique properties is becoming more and more important for studying the variation of materials’ properties with size and morphology [1–5]. Nanomaterials based on the scheelite-type have attracted considerable interest because of their luminescent property approved use in electrooptic applications [6–8]. SrWO4, CaWO4, PbWO4, and BaWO4 were considered to be typical oxides structure of scheelite-type. Locating within tetrahedral O-ion cages, W ions are isolated from each other in the scheelite structure, while Ca, Ba, Sr, and Pb ions are surrounded by eight oxygen ions [9]. CaWO4 with a scheelite structure is an important optical material, which has attracted particular interest because of its applications [10] in quantum electronics or scintillators as laser host material [11, 12]. CaWO4 powders are usually prepared by traditional solid-state reactions which require high temperature and harsh reaction conditions [13]. Recently, CaWO4 nanoparticles have been prepared by various wet chemical methods [14–18], which needs long reaction time, or nonaqueous solvents, such as hydrothermal method, citrate complex method, combustion process, coprecipitation, microwave-hydrothermal methods, polymeric precursor method, and microwave-solvothermal methods [19–22]. Therefore, to synthesize CaWO4 nanoparticles with a mild method (e.g., low temperature and/or quick reaction time) is of significance in both fundamental and applied studies [23]. In this paper, we report the synthesis, crystal structure, and fluorescence property of CaWO4 nanocrystals, which is prepared from the reaction of CaCl2 and Na2WO4 2H2O in the presence of PEG1000 by fast microwave-assisted method. By controlling the different reaction time, the degree of crystallinity of CaWO4 can be controlled. It means that we can obtain CaWO4 with higher crystallinity target structure by adjusting the reaction time, which is important for the preparation of aimed productions in
References
[1]
Y. Wang, J. Ma, J. Tao et al., “Synthesis of CaWO4 nanoparticles by a molten salt method,” Materials Letters, vol. 60, no. 2, pp. 291–293, 2006.
[2]
Y. Cui, Q. Wei, H. Park, and C. M. Lieber, “Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species,” Science, vol. 293, no. 5533, pp. 1289–1292, 2001.
[3]
M. H. Huang, S. Mao, H. Feick et al., “Room-temperature ultraviolet nanowire nanolasers,” Science, vol. 292, no. 5523, pp. 1897–1899, 2001.
[4]
J. Hu, T. W. Odom, and C. M. Lieber, “Chemistry and physics in one dimension: synthesis and properties of nanowires and nanotubes,” Accounts of Chemical Research, vol. 32, no. 5, pp. 435–445, 1999.
[5]
H.-W. Liao, Y.-F. Wang, X.-M. Liu, Y.-D. Li, and Y.-T. Qian, “Hydrothermal preparation and characterization of luminescent CdWO4 nanorods,” Chemistry of Materials, vol. 12, no. 10, pp. 2819–2821, 2000.
[6]
G. Blasse and W. J. Schipper, “Low-temperature photoluminescence of strontium and barium tungstate,” Physica Status Solidi (A), vol. 25, pp. K163–K165, 1974.
[7]
M. Martini, F. Meinardi, G. Spinolo, A. Vedda, M. Nikl, and Y. Usuki, “Shallow traps in PbWO4 studied by wavelength-resolved thermally stimulated luminescence,” Physical Review B, vol. 60, no. 7, pp. 4653–4658, 1999.
[8]
M. A. M. A. Maurera, A. G. Souza, L. E. B. Soledade et al., “Microstructural and optical characterization of CaWO4 and SrWO4 thin films prepared by a chemical solution method,” Materials Letters, vol. 58, no. 5, pp. 727–732, 2004.
[9]
M. Itoh and M. Fujita, “Optical properties of scheelite and raspite PbWO4 crystals,” Physical Review B, vol. 62, no. 19, pp. 12825–12830, 2000.
[10]
M. J. Treadaway and R. C. Powell, “Energy transfer in samarium-doped calcium tungstate crystals,” Physical Review B, vol. 11, no. 2, pp. 862–874, 1975.
[11]
S. Oishi and M. Hirao, “Growth of CaWO4 whiskers from KCl flux,” Journal of Materials Science Letters, vol. 8, no. 12, pp. 1397–1398, 1989.
[12]
M. Kobayashi, M. Ishii, Y. Usuki, and H. Yahagi, “Scintillation characteristics of PbWO4 single crystals at room temperature,” Nuclear Instruments and Methods in Physics Research A, vol. 333, no. 2-3, pp. 429–433, 1993.
[13]
G. Blasse and L. H. Brixner, “Ultraviolet emission from ABO4-type niobates, tantalates and tungstates,” Chemical Physics Letters, vol. 173, no. 5-6, pp. 409–411, 1990.
[14]
M. Sadegh, A. Badiei, A. Abbasi, H. Goldooz, and G. Mohammadi Ziarani, “Preparation of CaWO4:Ln3+@SiO2 (Ln=Tb, Dy and Ho) nanoparticles by a combustion reaction and their optical properties,” Journal of Luminescence, vol. 130, no. 11, pp. 2072–2075, 2010.
[15]
J. H. Ryu, J.-W. Yoon, C. S. Lim, W.-C. Oh, and K. B. Shim, “Microwave-assisted synthesis of nanocrystalline MWO4 (M: Ca, Ni) via water-based citrate complex precursor,” Ceramics International, vol. 31, no. 6, pp. 883–888, 2005.
[16]
Q. Xiao, Q. Zhou, and M. Li, “Synthesis and photoluminescence properties of Sm3+-doped CaWO4 nanoparticles,” Journal of Luminescence, vol. 130, no. 6, pp. 1092–1094, 2010.
[17]
J. k. Liu, Q. S. Wu, and Y. P. Ding, “Morphologies-controlled synthesis of CaWO4 crystals by a novel supramolecular template method,” Journal of Crystal Growth, vol. 279, no. 3-4, pp. 410–414, 2005.
[18]
E. F. Paski and M. W. Blades, “Analysis of inorganic powders by time-wavelength resolved luminescence spectroscopy,” Analytical Chemistry, vol. 60, no. 11, pp. 1224–1230, 1988.
[19]
L. Gracia, V. M. Longo, L. S. Cavalcante et al., “Presence of excited electronic state in CaWO4 crystals provoked by a tetrahedral distortion: an experimental and theoretical investigation,” Journal of Applied Physics, vol. 110, no. 4, Article ID 043501, 2011.
[20]
V. M. Longo, L. Gracia, D. G. Stroppa et al., “A joint experimental and theoretical study on the nanomorphology of CaWO4 crystals,” Journal of Physical Chemistry C, vol. 115, no. 41, pp. 20113–20119, 2011.
[21]
E. Orhan, M. Anicete-Santos, M. A. M. A. Maurera et al., “Towards an insight on the photoluminescence of disordered CaWO4 from a joint experimental and theoretical analysis,” Journal of Solid State Chemistry, vol. 178, no. 4, pp. 1284–1291, 2005.
[22]
L. S. Cavalcante, V. M. Longo, J. C. Sczancoski et al., “Electronic structure, growth mechanism and photoluminescence of CaWO4 crystals,” CrystEngComm, vol. 14, no. 3, pp. 853–868, 2012.
[23]
Y. Wang, J. Ma, J. Tao et al., “Synthesis of CaWO4 nanoparticles by a molten salt method,” Materials Letters, vol. 60, no. 2, pp. 291–293, 2006.
[24]
A. Kato, S. Oishi, T. Shishido, M. Yamazaki, and S. Iida, “Evaluation of stoichiometric rare-earth molybdate and tungstate compounds as laser materials,” Journal of Physics and Chemistry of Solids, vol. 66, no. 11, pp. 2079–2081, 2005.
[25]
F. Lei and B. Yan, “Hydrothermal synthesis and luminescence of CaMO4:RE3+ (M=W, Mo; RE=Eu, Tb) submicro-phosphors,” Journal of Solid State Chemistry, vol. 181, no. 4, pp. 855–862, 2008.
[26]
D. Chen, G. Shen, K. Tang, H. Zheng, and Y. Qian, “Low-temperature synthesis of metal tungstates nanocrystallites in ethylene glycol,” Materials Research Bulletin, vol. 38, no. 14, pp. 1783–1789, 2003.
[27]
S.-J. Chen, J. Li, X.-T. Chen, J.-M. Hong, Z. Xue, and X.-Z. You, “Solvothermal synthesis and characterization of crystalline CaWO4 nanoparticles,” Journal of Crystal Growth, vol. 253, no. 1–4, pp. 361–365, 2003.
[28]
R. Zhai, H. Wang, H. Yan, and M. Yoshimura, “Preparation of crystalline CaWO4 thin films by chemical bath deposition,” Journal of Crystal Growth, vol. 289, no. 2, pp. 647–651, 2006.
[29]
Z. L. Wang, G. Z. Li, and Z. W. Quan, “Nanostructured CaWO4, CaWO4/:Pb2+ and CaWO4:Tb3+ particles: polyol-mediated synthesis and luminescent properties,” Journal of Nanoscience and Nanotechnology, vol. 7, pp. 602–609, 2007.
[30]
T. Liu, J. Chen, and F. Yan, “Optical polarized properties related to the oxygen vacancy in the CaMoO4 crystal,” Journal of Luminescence, vol. 129, no. 2, pp. 101–104, 2009.
[31]
A. B. Campos, A. Z. Sim？es, E. Longo et al., “Mechanisms behind blue, green, and red photoluminescence emissions in CaWO4 and CaMoO4 powders,” Applied Physics Letters, vol. 91, no. 5, Article ID 051923, 2007.
