A new and efficient luminescence enhancement system of Eu–N-(3,5-dibromosalicylidene)-2-aminopyridine–1,10-phenanthroline and its application in the determination of trace amounts of europium

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 243–249

Contents lists available at SciVerse ScienceDirect

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa

A new and efficient luminescence enhancement system of Eu–N-(3,5-dibromosalicylidene)-2-aminopyridine–1,10-phenanthroline and its application in the determination of trace amounts of europium Lijuan Zhang, Xiaorui Zheng, Waqar Ahmad, Yunshan Zhou ⇑, Yugang An State Key Laboratory of Chemical Resource Engineering, Institute of Science, Beijing University of Chemical Technology, Beijing 100029, PR China

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

" A new ternary system composed of

Schiff base, phenanthroline and Eu is estabilished. " A simple yet sensitive method is built to determine trace amounts of Eu3+. " The energy transfer mechanism of the system is studied. " The luminescence enhancement is explained.

a r t i c l e

i n f o

Article history: Received 18 July 2012 Received in revised form 18 November 2012 Accepted 27 November 2012 Available online 6 December 2012 Keywords: N-(3,5-dibromo-salicylidene)-2-amino pyridine Europium(III) Luminescence enhancement 1,10-Phenanthroline Acetonitrile

a b s t r a c t A sensitive luminescence enhancement system has been developed for the determination of trace amounts of trivalent europium. The luminescence intensity of europium complex with N-(3,5-dibromosalicylidene)-2-aminopyridine (HL) was greatly enhanced after the addition of 1,10-phenanthroline (Phen) in acetonitrile solution. The excitation and emission wavelengths were 274 and 617 nm respectively. Under optimal conditions, the luminescence intensities varied linearly with Eu3+ concentration in the range of 4.0  10 6  2.4  10 5 mol L 1 with a detection limit of 4.3  10 10 mol L 1. This method was successfully applied to determine the trace amounts of Eu3+ in a high purity Gd2O3 matrix and in a mixed lanthanide sample. Energy transfer mechanism and luminescence enhancement of HL–Phen–Eu ternary system were studied. The results indicate that both HL and Phen are good sensitizers for the luminescence of Eu3+ ions, as energy gap between the lowest triplet level of HL/Phen and the resonant level of Eu3+ (5D1) exists around the optimal value (3000 ± 500 cm 1). The interference by some other lanthanide ions and common ions were also studied. Ó 2012 Elsevier B.V. All rights reserved.

Introduction Recently, luminescent lanthanide complexes have attracted great interest due to their broad applications in the fields of lumi⇑ Corresponding author. Address: Mailbox 99, 15 Beisanhuan East Road, Beijing University of Chemical Technology, Beijing 100029, PR China. Tel./fax: +86 10 64414640. E-mail address: [email protected] (Y. Zhou). 1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2012.11.086

nescence analysis [1], luminescence probe [2,3], electroluminescent materials [4], ‘‘Off–On–Off’’ luminescent signaling [5,6], and so on. This will inevitably cause more or less lanthanides to penetrate into the environment, food chains and harm the organisms, therefore methods for the determination of trace amounts of lanthanide ions are of great importance. In this respect, luminescence analysis of lanthanide ions with high sensitivity and selectivity has become an important research direction in the field of analytical chemistry [7–13].

244

L. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 243–249

However, lanthanide ions usually suffer from weak light absorption due to forbidden f ? f transitions (Laporte forbidden), which makes the direct excitation of metal ions very unefficient and inappropriate for exploring their applications [14,15]. This problem can be overcome by coupling organic ligand that can participate in energy transfer processes, known as ‘‘luminescence sensitization’’ or ‘‘antenna effect’’ [15–19]. The mechanism of antenna sensitization is comprised of the following three steps: light is absorbed by the organic ligands around the lanthanide ion, energy is transferred to the lanthanide ion from organic ligands, and then luminescence is generated from the lanthanide ion [3,15,20–22]. Previous studies have indicated that the ligands with rigid and conjugate structures can sensitize luminescence of lanthanide ions [23]. At present, b-diketonates [7,24,25] and aromatic carboxylic acids [9,25] were often employed as sensitizers for the luminescence of lanthanide ions. Besides this, the Schiff bases have attracted much attentions owing to the introduction of some special functional groups (C@O, C@N, and OH) in their structures and their convenient synthesis [26–30]. What is more, most of the Schiff bases have strong absorption in UV–Vis region which is beneficial to sensitize the luminescence of lanthanide ions through energy transfer process. On the other hand, most of the ligands cannot encapsulate the entire lanthanide ion, leaving some binding sites for solvent molecules [31,32], and thus causing a weak vibronic coupling between lanthanide ions and OAH, NAH, CAH oscillators of the coordinated solvent molecules. This leads to a facile path for radiationless deexcitation of lanthanide ion [3,21]. Therefore the ancillary ligand was usually used to replace coordination solvent molecules to enhance the luminescence of lanthanide complexes [7,8,11]. The ancillary ligand can transfer energy to lanthanide cation when the lowest triplet state of the ancillary ligand is suitable for the sensitization of lanthanide luminescence [8,33]. The ancillary ligand can also transfer the absorbed energy to the first ligand [12,13]. In another way, the ancillary ligand can also be used as an energy transfer path from the first ligand to the central metal ion [8]. In this context, 1,10-phenanthroline (Phen), 2,2-dipyridyl, ethyl sulfoxide, etc. were frequently used as the ancillary ligands to enhance the luminescence of lanthanide compounds [34,35]. Among them, Phen featuring conjugated planes including three aromatic rings and rigid structure, with N atoms having high electron density increases the orbital overlap between the lanthanide ions and ligand, which resulted enhance the energy transfer efficiency [35,36]. Based on the above analysis, we have developed a new ternary system of N-(3,5-dibromosalicylidene-2-aminopyridine)–Phen–Eu to determine trace amounts of Eu3+. The influence of organic solvent and concentration of reagents (HL, Phen and Eu3+) on the luminescence intensity of the system was systematically investigated. Under optimal condition of the system, the working curve for the determination of Eu3+ was constructed. This ternary system was successfully applied to determine the trace amounts of Eu3+ in a high purity Gd2O3 matrix and a mixed lanthanide samples. The mechanisms of energy transfer and luminescence enhancement were also studied in detail.

Experimental Apparatus Elemental analyses for C, H and N were determined by a Perkin– Elmer 240C analyzer. IR spectra were recorded on a Nicolet FT IR-170SX spectrometer using KBr pellets in the range of 400– 4000 cm 1. UV–Vis spectra were performed on a SHIMADZU UV2550 spectrophotometer in the range of 200–800 nm. The 1H

NMR spectrum of the Schiff base (HL) was recorded on a BRUKER AVANCE 600 spectrometer using DMSO as solvent and Me4Si as internal reference. The excitation and emission spectra were recorded on a Hitachi F-7000 fluorescence spectrometer equipped with a 150 W xenon lamp as the light source, both excitation and emission slit widths were 10 nm, PMT 500 V and scanning velocity 1200 nm min 1. Unless otherwise specified, the excitation wavelength and emission wavelength were 274 nm and 617 nm, respectively. Reagents All reagents were purchased commercially and used without further purification. A stock solution of Eu3+ (8  10 5 mol L 1) was prepared as follow: 0.88 g (2.5 mmol) of Eu2O3 (99.9%) was dissolved completely in 1.7 mL of concentrated nitric acid, evaporated under heating to near dryness, then diluted by 50 mL of relevant organic solvent in a 50 mL volumetric flask, resulting in a 0.1 mol L 1 Eu3+ solution. The resulting Eu3+ solution was diluted several times until a concentration of 8  10 5 mol L 1 was obtained. The HL stock solution (5  10 5 mol L 1) was prepared by adding appropriate amount of HL to 50 mL of relevant organic solvents. Phen stock solution (1  10 3 mol L 1) was prepared by adding appropriate amount of Phen to 50 mL of relevant organic solvents. Synthesis of ligand HL The ligand HL was synthesized according to the literature [37,38]. A solution of 3,5-dibromosalicylaldehyde (2.80 g, 10 mmol) in 50 mL of absolute ethanol was added drowpwise to the solution of 2-aminopyridine (0.94 g, 10 mmol) in 150 mL of absolute ethanol. Then this solution mixture was refluxed under stirring for 2 h in a 500 mL round bottom flask. The orange precipitates appeared, which were filtered and washed with 5  10 mL of ethanol, and then dried in vacuo for 24 h. The pure product was obtained after recrystallization from 200 mL of absolute ethanol, and the yield was 92% (3.4 g) [37,38]. Anal. Calcd. for C12H8ON2Br2 (%): C, 40.47; H, 2.25; N, 7.87. Found (%): C, 40.79; H, 2.29; N, 7.87. IR (cm 1) bands in KBr pellet: 3478 (tAOH), 3070 (tArAH), 1611 (tC@N), 1434, 1467, 1596 (tC@C), 1389 (dAOH), 1209 (tC@O), 690–879 (dAr@H). IR spectrum of the ligand HL is shown in Fig. S1 in the Supporting Information. 1H NMR (400 MHz, DMSO) (ppm): d = 9.54 (s, 1H), 8.57 (s, 1H), 7.98–7.89 (m, 3H), 7.57 (s, 1H); 7.42 (s, 1H). 1H NMR spectrum of the ligand HL in CD3COCD3 is shown in Fig. S2 in the Supporting Information. Synthesis of [Gd(L)2NO3]
3CH3CH2OH (1) To a suspension of HL (0.15 g, 0.4 mmol) in 4 mL of ethanol, a solution of NaOH (0.02 g, 0.5 mmol) in 4 mL of ethanol was added drop wise, the solution turned clear gradually. Then a solution of Gd(NO3)3
6H2O (0.40 g, 0.8 mmol) in 2 mL ethanol was added to the solution. The yellow precipitates appeared immediately, which were filtered off, washed with 4  5 mL ethanol and dried in vacuo. The yield was 44.5% (0.19 g). Anal. Calcd. for GdC30H34O8N5Br4 (%): C, 33.74; N, 6.56; H, 3.00; Found (%): C, 33.73; N, 6.52; H, 1.84. IR (cm 1) bands in KBr pellets: 3436 (tAOH); 1623 (tC@N); 1498, 1470, 1449 (tC@C); 1196 (tC@O); 704–872 (dAr@H). General procedure The appropriate volumes of HL, Eu3+ and Phen solution in this order were transferred to a 5 mL test tube. Then the mixture was

L. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 243–249

245

diluted to the volume of 4 mL with relevant organic solvents. The luminescence intensity of the blank (F0) and sample solution (F1) were measured at 617 nm by keeping the excitation wavelength at 274 nm at room temperature, DF values (F1 F0) were calculated in different conditions for investigation.

Results and discussion Spectral characteristics UV–Vis absorption spectral characteristics The UV–Vis absorption spectrum of HL is shown in Fig. 1 (curve a). HL displays four absorption bands at 229, 298, 309 and 364 nm, which are assigned to singlet–singlet 1p p absorptions of the aromatic rings [39]. The molar absorption coefficient value for HL at 298 nm is 3.5  104 L mol 1 cm 1, showing that HL is an adequate light-harvesting chromophore for the sensitization of lanthanide luminescence [39]. Fig. 1 reveals that by the addition of Eu3+ into the solutions of HL in acetonitrile, new absorption peaks appear at 425 nm. The bands located at 298 and 425 nm gradually increase, while the one at 364 nm decrease gradually with increasing Eu3+ concentrations. The two isosbestic points located at 330 and 380 nm confirm the formation of HL–Eu complexes [40]. It is also found that the absorbance remains unchanged when the concentration of Eu3+ remains higher than 5.0  10 6 mol L 1, indicating that the ligand HL in the solution has been reacted completely in the system. Luminescence spectral characteristics Emission spectra of Eu–HL–Phen, Eu–Phen and Eu–HL systems in acetonitrile were systematically studied (Fig. 2). The luminescence intensity of Eu–HL system was found to be enhanced by nine times after the addition of Phen. The emission spectra of the Eu–HL–Phen, Eu–Phen and Eu–HL systems exhibit characteristic sharp bands of the Eu3+ ion in the 590–720 nm spectral range. It was found that the luminescence intensity of the 5D0 ? 7F2 transition (electric dipole) at 617 nm was much stronger than that of the 5 D0 ? 7F1 transition (magnetic dipole) at 592 nm, which indicates that the coordination environment of the Eu3+ ion is devoid of inversion center when the ligands Phen and/or HL are coordinated to Eu3+ centers [41,42]. Therefore, the peak located at 617 nm was selected to monitor the luminescence intensity throughout the experiments.

Fig. 1. The UV–Vis spectra of HL (6.0  10 6 mol L 1) in acetonitrile and its Eu3+ complexes in different concentration of Eu3+ ions. Conditions: Eu3+: (a) 0.0 mol L 1; (b) 2.0  10 6 mol L 1; (c) 3.0  10 6 mol L 1; (d) 5.0  10 6 mol L 1; (e) 1.5  10 5 mol L 1; (f) 2.5  10 5 mol L 1; (g) 3.0  10 5 mol L 1; (h) 4.0  10 5 mol L 1.

Fig. 2. The emission spectra of Eu–HL–Phen (line a), Eu–Phen (line b), Eu–HL (line c) systems in acetonitrile solutions. Conditions: Eu3+, 2.0  10 5 mol L 1; HL, 6.0  10 6 mol L 1; Phen, 1.0  10 4 mol L 1.

Energy transfer in the system Determination of the triplet and singlet energy levels of HL Since the lowest excited state of Gd3+ (6P7/2) is too high to accept energy from ligand (HL), the data obtained from the phosphorescence spectrum of the complex reveal the triplet energy level of the corresponding ligand [32,43]. From the phosphorescence spectrum of [Gd(L)2NO3]
3CH3CH2OH (1) at 77 K (Fig. 3), the triplet energy level of HL was found to be 22,124 cm 1 (452 nm). The triplet energy level of Phen is known as 22,200 cm 1 [44]. As shown in Fig. 1 (curve a), the singlet state level (1pp) of HL can be estimated by the boundary tangent of its UV–Vis absorbance (264 nm) that is 37, 878 cm 1. Process of the energy transfer The commonly accepted mechanism for photoluminescence of Eu3+ is antenna effect [10,13]. Upon UV irradiation, the organic ligands of Eu-complex are excited to a vibrational level of the first excited singlet state (1S) from the ground state (0S). Then, the excited singlet state (1S) can undergo nonradiative intersystem crossing from the singlet state (1S) to the triplet state (3T). The triplet state (3T) can undergo nonradiative transition to electronic transition levels of Eu3+. After this indirect excitation by energy transfer, the ground state of Eu3+ can be excited to the excited state energy levels. Finally, the Eu3+ emits luminescence when transition to the ground state occurs (Fig. 4).

Fig. 3. The phosphorescence spectrum of [Gd(L)2NO3]
3CH3CH2OH (1) at 77 K (the excitation wavelength 277 nm).

246

L. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 243–249

Fig. 4. Schematic energy level diagram and the energy transfer process. 0S, ground state; 1S, singlet state; 3T, triplet state.

According to the Reinhoudt’s empirical rule, the intersystem crossing process becomes effective only when DE (1pp 3pp) is at least 5000 cm 1 [45]. The energy gap DE (1pp 3pp) of HL is 15754 cm 1 (>5000 cm 1), which indicates that the intersystem crossing process of HL is effective. Furthermore, on the basis of the intramolecular energy transfer mechanism, for a ligand to be a suitable sensitizer, an optimal value of the energy gap between the triplet energy level of the ligand and the resonant energy level of Eu3+ ion is assumed to exist around 3000 ± 500 cm 1 [39,46]. The larger or the smaller energy difference may result in a decrease of photoluminescent intensities of the Eu-complexes. With respect to the aim of this work, the energy gap between triplet state of HL and resonance state (5D1) of Eu3+ is 3360 cm 1, which is an ideal situation for the sensitization of Eu3+ luminescence (Fig. 4). Fig. 2 shows that the luminescence intensity of Eu–HL system was greatly increased by the introduction of ancillary ligand (Phen). Since most of the ligands cannot encapsulate the entire Eu3+ ion, leaving some binding sites for solvent molecules [31,32], and resulting in a weak vibronic coupling between Eu3+ ion and OAH, NAH, CAH oscillators of the coordinated solvent molecules. This leads to a facile path for radiationless deexcitation of Eu3+ ion [3,21]. Therefore the ancillary ligand was usually used to replace coordination solvent molecules to enhance the luminescence of Eu3+ ion complexes [7,8,11]. Here Phen was used as an ancillary ligand to increase the luminescence intensity of Eu3+ ion with the following two roles: first, Phen can replace some coordination solvent molecules to avoid a weak vibronic coupling between Eu3+ ions and OAH, NAH, CAH oscillators of the coordinated solvent molecules. Second, Phen can transfer energy to Eu3+ ion effectively. The energy gap (3336 cm 1) between the lowest triplet level of Phen (22,100 cm 1) and the resonance level of Eu3+ (18,764 cm 1, 5D1) exists around optimal value (3000 ± 500 cm 1), indicating that Phen is a suitable sensitizer for the luminescence of Eu3+ (Fig. 4) [46–48]. The triplet energy level of HL (22,124 cm 1) is close to Phen, so both HL and Phen enhance the luminescence intensity of Eu–HL–Phen system [21]. What is more, the concentration of Phen (1.0  10 4 mol L 1) is about 17 times of HL (6.0  10 6 mol L 1) in the system, indicating that excess of Phen form a protective shield around Eu3+ to prevent the luminescence quenching [22]. Fig. 5 shows the luminescence spectral changes of HL–Phen system before and after the addition of Eu3+. According to the Fröster

Fig. 5. The luminescence emission spectra of HL–Phen (line a) and Eu–HL–Phen (line b). Conditions: Eu3+, 2.0  10 5 mol L 1; HL, 6.0  10 6 mol L 1; Phen, 1.0  10 4 mol L 1.

Fig. 6. The influence of solvents on the luminescence intensity of the Eu–HL–Phen system ((a) CH3CN; (b) CHCl3; (c) CH3CH2OH; (d) CH3OH). Conditions: Eu3+, 2.0  10 5 mol L 1; HL, 6.0  10 6 mol L 1; Phen, 1.0  10 4 mol L 1.

Fig. 7. The influence of the concentration of HL on the luminescence intensity of the Eu–HL–Phen system. Conditions: Eu3+, 2.0  10 5 mol L 1; Phen, 1.0  10 4 mol L 1.

theory [48,49], Ea = 1 Ida/Id, the energy transfer efficiency Ea can be calculated, where Ida and Id are the luminescence intensities of the donor in the presence and in the absence of acceptor, respectively. It can be found that Ida and Id are 253 and 347 at 359 nm

247

L. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 243–249

Fig. 8. Influence of the concentration of Phen on the luminescence intensity of the Eu–HL–Phen system. Conditions: Eu3+, 2.0  10 5 mol L 1; HL, 6.0  10 6 mol L 1.

Fig. 9. The calibration graph for the determination of Eu3+. Conditions: HL, 6.0  10 6 mol L 1; Phen, 1.0  10 4 mol L 1.

in Fig. 5 and the calculated energy transfer efficiency of Eu– HL–Phen is Ea = 0.27, hence HL and Phen can sensitize the luminescence of Eu3+.

rapidly (<1 min) at ambient environmental conditions and the luminescence intensity could maintain stability for at least 100 min under normal conditions, thus there was no need to strictly control the reaction time.

Optimization of experimental conditions Influence of solvents The luminescence intensity is importantly influenced by the polarities of different organic solvents, although the luminescence properties of lanthanide complexes are mainly governed by the chemical structures of the complexes. The luminescence enhancing effect of organic solvents in Eu–HL–Phen system follows the order of CH3CN > CHCl3 > CH3CH2OH > CH3OH (Fig. 6). The permittivity (e) values for these solvents are 37.5 (CH3CN), 4.7 (CHCl3), 24.3 (CH3CH2OH), 32.6 (CH3OH). The order of the luminescence intensity in the system is not in agreement with the permittivity value of the solvents [50]. CH3CN was found to be the best among the four solvents, mainly because of its poor coordination ability (compared with the other solvents) with Eu3+ [8]. When both Schiff base ligand (HL) and Phen react with Eu3+, they may not be able to completely encapsulate the metal cation but leave some binding sites for the solvent molecules [31], in other word, they could not absolutely prevent the solvent molecules from entering to coordinate with Eu3+. The more easier the solvent molecules enter to coordinate with Eu+3, the more the energy is consumed (which the ligand triple level transfers to the emitting level of Eu3+). As a consequence, the luminescence intensity of the system is reduced. The result herein implied that not only polarity but also coordination ability of the solvent are important factors for the luminescence intensity in the system. Besides, it is reasonable to understand that the luminescence intensity of Eu3+ is decreased significantly in the presence of CH3CH2OH and CH3OH which are efficient luminescence quencher through multiphonon relaxation[51]. Therefore, acetonitrile was chosen as a suitable solvent. Influence of reaction time The influence of reaction time on the luminescence intensity was investigated. The results showed that the reactions proceed

Influence of the concentration of HL The influence of the concentration of HL on the luminescence intensity of Eu–HL–Phen system is shown in Fig. 7. It can be found that the luminescence intensity increases with the increase of HL concentration. When the concentration of HL reaches up to 6.0  10 6 mol L 1, the luminescence intensity starts decreasing gradually due to the appearance of more and more C@N in the system [52]. Consequently, the concentration of HL was employed in 6.0  10 6 mol L 1 in the further experiments. Influence of the concentration of Phen The influence of the concentration of Phen on luminescence intensity of Eu–HL–Phen system was investigated in detail. Fig. 8 shows that the luminescence intensity of the system reaches maximum when the concentration of Phen is controlled at 1.0  10 4 mol L 1. Above this concentration the luminescence intensity decreases owing to the reagent self-absorption. Therefore, 1.0  10 4 mol L 1 was selected as optimum concentration of Phen in the further experiments. Influence of some other lanthanides, common cations and anions In order to evaluate the practical applicability of the present method for the determination of trace amounts of Eu3+ ions in real samples, the potential interferences of foreign species on the photoluminescence intensity and determination were tested. The chemicals used herein included Cu(NO3)2
3H2O, Mg(NO3)2
6H2O, Na2SO4, Fe(NO3)3
9H2O, Cd(NO3)2
4H2O, LiNO3, Co(NO3)2
6H2O, NaCl, KBr. All the lanthanides used herein were prepared with the procedure similarly to that for Eu3+ stock solution described above. The tolerance allowed in the variation of the luminescence intensity was ±10%. The maximum tolerable concentrations of

Table 1 Effect of some other lanthanides, common cations and anions as a maximum tolerable concentration. Coexisting Ln3+ ions

La

Ce

Pr

Nd

Sm

Tb

Gd

Dy

Ho

Er

Yb

Y

Ratio (Ln/Eu) Coexisting X ions

4.5 Na+

5.0 K+

5.5 Mg2+

1.5 Co2+

1.0 Li+

2.0 Cu2+

6.5 Cd2+

0.25 Fe3+

3.5 Cl

3.7 Br

0.15

0.2

Ratio (X/Eu)

60

50

5

3.5

40

2

3.5

4

60

50

SO24 50

248

L. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 243–249

Table 2 Determination of Eu3+ in high purity Gd2O3 matrix. Samples

Added (Eu3+) (10

5

1

1.300

1.290 1.291 1.279 1.297 1.314

2

1.750

3

4

mol L

1

)

Found (10

5

mol L

1

)

5

RSD (%)

1.294 ± 0.016

99.54

0.99

1.750 1.756 1.771 1.764 1.775

1.763 ± 0.011

100.7

0.50

2.000

1.975 2.004 2.018 2.023 2.051

2.014 ± 0.034

100.7

1.37

2.700

2.692 2.700 2.693 2.704 2.687

2.695 ± 0.008

99.81

0.25

Known Eu3+ (10 5 mol L 1)

Found Eu3+ (10 5 mol L

1.000

1.006, 1.012, 1.004, 1.027, 1.053

1

)

Average (10 5 mol L

1

1.020 ± 0.025

)

Recovery (%)

RSD

102.0

1.99

some other lanthanides, some common cations and anions are listed in Table 1. Analytical characters The calibration graph (Fig. 9) for the determination of Eu3+ was acquired under the optimal conditions. The linear equation of DF = 2289.46c 760.52 (where c is 10 5 mol L 1 and represents the concentration of Eu3+ with a linear correlation coefficient of 0.99954) was obtained in the range of 4.0  10 6 2.4  10 5 mol L 1. The limit of detection (LOD) was 4.3  10 10 mol L 1 (LOD = Kd/S, where K is the constant that is 3, d represents the standard deviations of 10 blank readings and S represents the slope of the linear calibration curve). Application of the method The above method was used for the determination of trace amounts of Eu3+ in a high purity Ga2O3 matrix and in a synthetic sample of lanthanide oxides which was composed of La (417 lg), Ce (560 lg), Pr (564 lg), Nd (144 lg), Sm (120 lg), Gd (786.5 lg), Dy (24 lg), Ho (495 lg), Er (502 lg), Yb (17 lg), Y (9 lg) per 100 mL of solution. It can be concluded from the results listed in Tables 2 and 3, that the proposed procedure is a sensitive, simple, and rapid method compared with other methods [53–56] for the determination of Eu3+. Conclusions In this study, the optimal conditions including reaction time, concentration ratio of each component in HL–Eu–Phen ternary system were founded, and a new and efficient system by the luminescence analysis have been established for the determination of trace

mol L

1

Recovery (%)

Table 3 Determination for Eu3+ in a synthetic sample of lanthanide oxide.

Confidence interval (10

)

amounts of Eu3+. The interference of other lanthanides, some common cations and anions on the luminescence intensity of the ternary system under the optimal conditions were also studied. Both the triplet states of the Schiff base (HL) and Phen match the resonant level of Eu3+ (5D1), therefore both of them can transfer energy to Eu3+ and can sensitize luminescence of Eu3+. This method was successfully applied to determine the trace amounts of Eu3+ in high purity Gd2O3 matrix and a mixed lanthanide sample. The proposed procedure is, easy to handle, rapid, simple and sensitive. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2012.11.086. References [1] W. Yang, X.L. Teng, M. Chen, J.Z. Gao, L. Yuan, J.W. Kang, et al., Talanta 46 (1998) 527–532. [2] J. Hynes, T.C. O’Riordan, A.V. Zhdanov, G. Uray, Y. Will, D.B. Papkovsky, Anal. Biochem. 390 (2009) 21–28. [3] F.S. Richardson, Chem. Rev. 82 (1982) 541–552. [4] A. Edwards, C. Claude, I. Sokolik, T.Y. Chu, Y. Okamoto, R. Dorsinville, J. Appl. Phys. 82 (1997) 1841–1846. [5] C. Bazzicalupi, A. Bencini, A. Bianchi, C. Giorgi, V. Fusi, A. Masotti, et al., Chem. Commun. 7 (2000) 561–562. [6] T. Gunnlaugsson, J.P. Leonard, K. Senechal, A.J. Harte, J. Am. Chem. Soc. 125 (2003) 12062–12063. [7] F.F. Dang, Y. Li, W.S. Liu, Spectrochim. Acta Part A 66 (2007) 676–680. [8] F.F. Dang, W.S. Liu, J.R. Zheng, Spectrochim. Acta Part A 67 (2007) 714–718. [9] Y.X. Ci, M.Z. Ning, F.Y. Yang, Chem. J. Chin. Univ. 4 (1983) 115–118. [10] S.B. Meshkova, V.E. Kuz’min, Y.E. Shapiro, Z.M. Topilova, I.V. Yudanova, D.V. Bol’shoi, et al., J. Anal. Chem. 55 (2) (2000) 102–108. [11] N.M. Sita, T.P. Rao, C.S.P. Iyer, A.D. Damodaran, Talanta 44 (1997) 423–426. [12] W. Yang, Z.L. Mo, X.L. Teng, M. Chen, J.Z. Go, L. Yuan, et al., Analyst 123 (1998) 1745–1748. [13] G. Zhao, S. Zhao, J. Gao, J. Kang, W. Yang, Talanta 45 (1997) 303–307. [14] A. Beeby, S.W. Botchway, I.M. Clarkson, S. Faulkner, A.W. Parker, D. Parker, et al., J. Photochem. Photobiol. B 57 (2000) 83–89. [15] Y.J. Cui, Y.F. Yue, G.D. Qian, B.L. Chen, Chem. Rev. 112 (2012) 1126–1162. [16] K. Binnemans, Chem. Rev. 109 (2009) 4283–4374. [17] E.G. Moore, A.P.S. Samuel, K.N. Raymond, Acc. Chem. Res. 42 (2009) 542–552. [18] N. Sabbatini, M. Guardigli, J.M. Lehn, Coord. Chem. Rev. 123 (1993) 201–228. [19] S.I. Weissman, J. Chem. Phys. 10 (1942) 214–217. [20] J.C.G. Bünzli, C. Piguet, Soc. Rev. 34 (2005) 1048–1077. [21] G.Z. Chen, Fluorescence Spectroscopy, Science Press, Beijing, 1975. pp. 26–33. [22] G.Y. Hong, Fundamental and Application of Rare Earth Luminescent Materials, Science Press, Beijing, 2011. pp. 413–427. [23] D.E. Ryan, F. Snapeand, M. Winpe, Anal. Chim. Acta 58 (1972) 101–106. [24] I. Hemmilä, Anal. Chem. 57 (1985) 1676–1681.

L. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 243–249 [25] N. Arnaud, E. Vaquer, J. Georges, Analyst 123 (1998) 261–265. [26] Y.T. Yang, K. Driesen, P. Nockemann, K.V. Hecke, L.V. Meervelt, K. Binnemans, Chem. Mater. 18 (2006) 3698–3704. [27] W. Chen, Y.G. Li, Y.M. Cui, X. Zhang, H.L. Zhu, Q.F. Zeng, Eur. J. Med. Chem. 45 (2010) 4473–4478. [28] J.Z. Zhao, B. Zhao, J.Z. Liu, X. Wang, D.L. Qiu, L. Sun, et al., Chem. J. Chin. Univ. 22 (2001) 136–138. [29] J.Z. Zhao, B. Zhao, W.Q. Xu, J.Z. Liu, Chem. J. Chin. Univ. 24 (2004) 324–328. [30] M.R. Ganjali, M. Hosseini, M. Hariri, P. Norouzi, A.A. Khandar, A. Bakhtiari, Mater. Sci. Eng. 30 (2010) 929–933. [31] M.S. Liu, Q.Y. Yu, Y.P. Cai, C.Y. Su, X.M. Lin, X.X. Zhou, et al., Cryst. Growth Des. 8 (2008) 4083–4091. [32] M. Latva, H. Takalo, V.M. Mukkala, C. Matachescu, J.C. Rodriguez-Ubis, J. Kankare, J. Lumin. 75 (1997) 149–169. [33] F.F. Dang, W.S. Liu, Microchim. Acta 158 (2007) 111–116. [34] S. Lis, Z. Hnatejko, P. Barczynski, M. Elbanowski, J. Alloys Compd. 344 (2002) 70–74. [35] B. Juskowiak, I. Grzybowska, E. Galezowska, S. Takenaka, Anal. Chim. Acta 512 (2004) 133–139. [36] T. Cardinaels, J. Ramaekers, P. Nockemann, K. Driesen, K.V. Hecke, L.V. Meervelt, et al., Chem. Mater. 20 (2008) 1278–1291. [37] A.M. Issam, J. Ismail, J. Appl. Polym. Sci. 100 (2006) 1198–1204. [38] S. Arunachalam, N.P. Priya, K. Boopathi, C. Jayabalakrishnan, V. Chinnusamy, Appl. Organometal. Chem. 24 (2010) 491–498. [39] M.V. Lucky, Sarika Sivakumar, M.L.P. Reddy, Avijit Kumar Paul, Srinivasan Natarajan, Cryst. Growth Des. 11 (2011) 857–864.

249

[40] C. Sousa, P. Gameiro, C. Freire, B.D. Castro, Polyhedron 23 (2004) 1401–1408. [41] G. Phaomei, R.S. Ningthoujam, W.R. Singh, N.S. Singh, M.N. Luwang, R. Tewari, et al., Opt. Mater. 32 (2010) 616–622. [42] H.J. Zhang, B. Yan, S.B. Wang, J.Z. Ni, J. Photochem. Photobiol. A 109 (1997) 223–228. [43] S. Biju, D.B. AmbiliRaj, M.L.P. Reddy, B.M. Kariuki, Inorg. Chem. 45 (2006) 10651–10660. [44] X.J. Yu, Q.D. Su, J. Photochem. Photobiol. A 155 (2003) 73–78. [45] F.J. Steemers, W. Verboom, D.N. Reinhoudt, E.B.V. Tol, J.W. Verhoeven, J. Am. Chem. Soc. 117 (1995) 9408–9414. [46] B. Xu, B. Yan, Spectrochim. Acta Part A 66 (2007) 236–242. [47] M. Irfanullah, K. Iftikhar, J. Fluoresc. 21 (2011) 673–686. [48] R.M. Clegg, Curr. Opin. Biotechnol. 6 (1995) 103–110. [49] G.A. Kumar, N.V. Unnikrishnan, J. Photochem. Photobiol A 144 (2001) 107– 117. [50] T.L. Yang, W.W. Qin, W.S. Liu, J. Anal. Chem. 60 (2005) 325–329. (51) M.N. Luwang, R.S. Ningthoujam, Jagannath, S.K. Srivastava, R.K. Vatsa, J. Am. Chem. Soc. 9 (2010) 2759–2768. [52] L. Li, Y.Q. Dang, H.W. Li, B. Wang, Q. Wu, Tetrahedron Lett. 51 (2010) 618– 621. [53] H.B. He, W.J. Zhang, G.Z. Ma, H.X. Shen, Chin. J. Anal. Chem. 29 (2001) 1125– 1128. [54] C.E. Lisowski, J.E. Hutchison, Anal. Chem. 81 (2009) 10246–10253. [55] S. Liawruangrath, S. Sakulkhaemaruethai, Talanta 59 (2003) 9–18. [56] J.P. Chen, Y.Y. Liu, Chem. Res. Appl. 23 (2011) 137–144.