ОПТИКА И СПЕКТРОСКОПИЯ, 2015, том 118, № 1, с. 129-134
СПЕКТРОСКОПИЯ ^^^^^^^^^^
КОНДЕНСИРОВАННОГО СОСТОЯНИЯ
УДК 535.37
SYNTHESIS, CHARACTERIZATION, AND LUMINESCENCE PROPERTIES OF (Li, La)VO4/(Li, La)PO4: Eu3+ PHOSPHORS
© 2015 г. Xiaochun Zhou* and Xiaojun Wang**
* School of Chemistry and Chemical Engineering, Jinggangshan University, 343009 Ji'an, Jiangxi, China ** Mechanical and Electronic Department of Guangdong Polytechnic Normal University, 510635 Guangzhou, China
E-mail: ncdxzxc@163.com Received January 19, 2014
The different morphological varieties of (Li0 75, La0 75)VO4, (Li0 75, La0 75)PO4 and (Li0 75, La0 75)PO4 nano-phosphors have been synthesized by reaction chemistry method. A ratio of starting raw material (Li075, La0 75)VO4 synthesis route generated the meteoric stone-like particles, and ratio of starting raw material (Li0 75, La0 75)PO4 without cationic surfactant cetyltrimethylammonium bromide (CTAB) synthesis route generated the cloud-like particles, while a ratio of starting raw material (Li075, La075)PO4 with CTAB synthesis route led to the formation of the sesame-like nanoparticles. Upon photoluminescence study of the as-prepared samples, the chromaticity of the dopant ion was found to be sensitive to the host morphology as well as the preparative ratio of starting raw material adopted for sample fabrication.
DOI: 10.7868/S0030403415010286
Lanthanide (Ln) doped nanomaterials (NMs) show superior chemical and optical properties, these unique properties, coupled with size- and shape-independent luminescent phenomena, make Ln3+ doped nanocrystals (NCs) have applications in a very wide range of fields. Codoping is a widely applied technological process in Ln3+ doped luminescent materials science that involves incorporating atoms or ions of appropriate elements into host lattices, to yield hybrid materials with desirable properties such as modifying the electronic properties [1], stabilizing a specific crystallographic phase [2] or tuning emission properties [3]. It has been reported that doping other ions such as Li+, Al3+ and Zn2+ can also significantly enhance the luminescence in GdTaO4: Eu3+ [4]. Lithium ion has been introduced into different phosphor host lattices such as Y2O3 : Eu3+ [5] and MgO : Eu3+ [6], acting as a co-activator and charge compensator. Especially [7], photoluminescence (PL) of SrTiO3— (Li0 5La0 5)TiO3 : Pr system was investigated, highly enhanced photoluminescence of SrTiO3:Pr by substitution of (Li05, La05) pair for Sr, and this revealed that the Li+ addition strongly affects the morphology of particles as well as the photoluminescent efficiency of phosphors.
Among all of rare eath (RE) doped luminescence materials, lanthanide orthovanadates (LnVO4) have many fascinating characteristics and are widely used as luminescence materials [8]. Recently, much attention have been paid to P-doping of LnVO4 to design new luminescence materials [9, 10], because both phos-
phates and vanadates share common physical and chemical properties [11].
In this study, we attempted to obtain an enhanced luminescence effect in Eu3+ doped ratio of starting raw material (Li0 75, La0.75)VO4, (Lio.75, La0.75)PO4 and (Li0 75, La075)PO4 by using cationic surfactant cetyltrimethylammonium bromide (CTAB). To the best of our knowledge, the synthesis and luminescent properties of the ratio of starting raw material (Li075, La075)VO4, (Li0.75, La0.75)PO4 and (L^.75, La0js)PO4 by using CTAB nanophosphors have been seldom reported. Herein, we present a facile chemistry method for synthesis, structure characteriazation and photoluminescent properties of the Eu3+ doped ratio of starting raw material (Li0 75, La0 75)VO4, (Lio.75, La0 75)PO4 and (Li0 75, La0 75)PO4 by using CTAB phosphors.
EXPERIMENTAL
Synthesis of Eu3+ Doped Ratio of Starting Raw Material (Li0 La0.7s)VO4
Eu3+ doped ratio of starting raw material (Lio.75, La0 75)VO4 phosphors were prepared by a facile chemistry method. Firstly, the 0.1 mmol Eu2O3 was dissolved in concentrated nitric acid to form Eu(NO3)3. Secondly, 0.01 x 0.75 mol LiNO3, 0.01 x 0.75 mol La(NO3)3 • 6 H2O and 0.01 mol NH4VO3 were put into the Eu(NO3)3 at a certain speed. Thirdly, 10 mL deionized water was added to the above mixture. The stirring was continued till the mixture became a solution. The solution was dried at 90°C to yield a xerogel. The obtained xerogel was placed into a furnace pre-
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Fig. 1. Low- and high-magnication SEM images Eu3+-doped ratio of starting raw material (Li0 75, La0 75)VO4.
heated to a definite temperature (740°C) and calcined for 40 min.
Synthesis of Eu3+ Doped Ratio of Starting Raw Material (Lio.75, La0J5)PO4
Eu3+ doped ratio of starting raw material (Li0 75, La075)PO4 phosphors were prepared by a facile chemistry method. Firstly, the 0.1 mmol Eu2O3 was dissolved in concentrated nitric acid to form Eu(NO3)3. Secondly, 0.01 x 0.75 mol LiNO3, 0.01 x 0.75 mol La(NO3)3 • 6 H2O and 0.01 mol (NH4)2HPO4 were put into the Eu(NO3)3 at a certain speed. Thirdly, 10 mL deionized water was added to the above mixture. The stirring was continued till the mixture became a solution. The solution was dried at 90°C to yield a xerogel. The obtained xerogel was placed into a furnace preheated to a definite temperature (740°C) and calcined for 40 min.
Synthesis of Eu3+ Doped Ratio ofStarting Raw Material (Li0.75, La0 75)PO4 by Using CTAB
Eu3+ doped ratio of starting raw material (Li0 75, La075)PO4 phosphors were prepared by a facile chemistry method. Firstly, the 0.1 mmol Eu2O3 was dissolved in concentrated nitric acid to form Eu(NO3)3. Secondly, 0.01 x 0.75 mol LiNO3, 0.01 x 0.75 mol La(NO3)3 • 6 H2O and 0.01 mol (NH4)2HPO4 were put into the Eu(NO3)3 at a certain speed. Thirdly, 10 mL deionized water and 2.5 mmol (CTAB) were added to the above mixture. Then the obtained deposition was aged in 40°C water for 1 h. The precursor was gained through the process of drying at 90°C. In the last step, the obtained precursor was placed into a furnace preheated to a definite temperature (740°C) and calcined for 40 min.
X-ray diffraction (XRD) patterns were measured using a BRUKERD8 FOCUS with Cu Ka radiation (^ = 0.15418 nm), at a scanning rate of 4.0° min-1. PL emission/excitation spectra were measured using an
F — 4500 fluorescence spectrometer (Hitachi). The sizes and morphologies of the as-synthesized samples were studied by JSM-6380LA (JEOL) scanning electron microscope (SEM). Fourier transform infrared spectroscopy (FTIR, AVATAR370) were used to measure phosphors powder with the KBr pellet technique. All the measurements were carried out at room temperature.
RESULTS AND DISCUSSION
Morphology of Phosphors
Figure 1 shows low- and high-magnication SEM images of Eu3+ doped ratio of starting raw material (Li0 75, La075)VO4 (Fig. 1) prepared by a facile chemistry method. It can be seen that the morphology of the phosphors exhibits meteoric stone-like particles. Figures 2a, b shows low- and high-magnication SEM images of Eu3+ doped ratio of starting raw material (Li0.75, La0.75)PO4 prepared by a facile chemistry method. It can be seen that the morphology of the phosphors exhibits cloud-like particles without CTAB, and exhibits sesame-like particles with CTAB. The result shows that the Eu3+ doped different ratio of starting raw material obtained morphology of final product is different.
X-ray Diffraction (XRD) Patterns
The X-ray diffraction (XRD) patterns of the Eu3+ doped ratio of starting raw material (Li075, La0 75)VO4 phosphors are shown in Fig. 3. A mixture of mono-clinic and tetragonal LaVO4 can be observed from Fig. 3. The main products are monoclinic LaVO4, together with a small amount of tetragonal LaVO4 detected as parent peaks at around 29 = 24°. The XRD patterns of Li3VO4 is hardly showed from Fig. 3, according to the previous report literature data [12]. The X-ray diffraction (XRD) patterns of the Eu3+ doped ratio of starting raw material (Li075, La0 75)PO4 phosphors are shown in Figs. 4a, b. A monoclinic LaPO4
(a)
Fig. 2. Low- and high-magnication SEM images Eu3+ doped ratio of starting raw material (Li0 75, La0 75)PO4 (a) without CTAB; (b) with CTAB.
can be observed from Figs. 4a, b, according to the previous report literature data [13], at the same time, experimental results show that there is no evident influence of the CTAB on the structures. The XRD patterns of Li3VO4 is hardly showed from Figs. 4a, b, according to the previous report literature data [12], but diffraction intensity of the strongest peak was remarkably changed. It is likely that much better crystal-linity of the with CTAB samples, because diffraction intensity of the strongest peak of the with CTAB samples is stronger than that of without CTAB (shown in Figs. 4a, b).
FTIR Spectra
Fig. 5 shows the FTIR spectra of the Eu3+ doped ratio of starting raw material (Li0 75, La0.75)VO4 phosphors. A mixture of monoclinic and tetragonal LaVO4 can be observed from Fig. 5. The result almost have no difference with the previous report literature data [14]. Figs. 6a, b shows the FTIR spectra of the Eu3+ doped ratio of starting raw material (Li0 75, La0 75)PO4 phosphors. The peaks of v3: 955,' 994, 1020, 1060, 1093 cm-1 and v4: 541, 566, 578, 622 cm-1 can be observed from Figs. 6a, b, these patterns confirm that the specimen is typical monoclinic LaPO4 structure [15].
Photoluminescence Properties
The excitation and emission spectra of Eu3+ doped ratio of starting raw material (Li0 75, La0 75)VO4 phosphors were shown in Fig. 7 (^em = 616 nm). The broad luminescent band ranged from 200 to 350 nm with a maximum at 313 nm in the spectra. This band is ascribed to a charge transfer from the oxygen ligands to
the central vanadium atom inside the VO4 ion, sug-
Intensity, a.u 400
300
200
100
10 20 30 40
50 60 29, deg
Fig. 3. XRD patterns Eu terial (Li075, La0.75)VO4
3+
doped ratio of starting raw ma-
Intensity, a.u. 300
200
100 -
Intensity, a.u. 400
300 -
200 -
1
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