(Solid + Liquid) Phase Equilibria for the Systems CsBr + EuBr3 + H2O

Article pubs.acs.org/jced

(Solid + Liquid) Phase Equilibria for the Systems CsBr + EuBr3 + H2O and CsBr + EuBr3 + HBr (∼12.3%) + H2O at 298.15 K and Atmospheric Pressure and Thermodynamic and Fluorescent Properties of the New Solid-Phase Compound Meng-Yao Su, Zhan-Ping Qiao,* Yuan-Lin Dang, and Xin Chen College of Chemistry and Pharmaceutical Engineering, Nanyang Normal University, Nanyang 473000, People’s Republic of China

ABSTRACT: In this study, the (solid + liquid) phase equilibria for the two systems of CsBr + EuBr3 + H2O and CsBr + EuBr3 + HBr (∼12.3%) + H2O at 298.15 K and atmospheric pressure were determined by isothermal solubility method. Schreinemaker wet residue approach was used to determin the solid phases obtained from the studied systems. The related phase diagrams were depicted based upon the experimental data. There were two invariant points, three invariant curves, and three crystallization fields corresponding to CsBr, 5CsBr·2EuBr3·20H2O, and EuBr3·6H2O in the two phase diagrams. New double salt 5CsBr· 2EuBr3·20H2O was incongruently soluble in the two systems. The content of EuBr3 in two invariant points decreased as the concentration of HBr in equilibrium liquid phase increased, while that of CsBr changed a little. The new solid-phase compound 5CsBr·2EuBr3·20H2O was investigated using chemical, XRD, and TG-DTG analyses. Additionally, the standard molar enthalpy of solution for 5CsBr·2EuBr3·20H2O in water was confirmed to be 104.69 ± 0.88 kJ/mol by microcalorimetry; its standard molar enthalpy of formation was determined as being −(9659.7 ± 1.6) kJ/mol. The fluorescence excitation and emission spectra of 5CsBr·2EuBr3·20H2O were acquired. The results indicate that upconversion spectra of 5CsBr·2EuBr3·20H2O exhibited pure green upconversion luminescence under 785 nm excitation.

1. INTRODUCTION Many new compounds of rare-earth elements have been applied successfully in many fields, such as medical diagnosis, sensor technology, bioimaging probes, antibacterial material, wavelength-converting materials, phosphors, and so on.1−5 Furthermore, their thermodynamic properties are significant in theoretical research and practical applications. Researchers have been paying great attention to the work of exploring and studying thermodynamic properties of these compounds.6−8 Some potential upconversion materials, such as Er3+-doped RbGd2C17 and RbGd2Br7; Cs3Yb2Cl9 and Cs3Yb2Br9; Cs3Y2Br9 (10% Dy3+ and Cs3Dy2Br9); Cs3Er2X9 (X = Cl, Br, I); and Er3+ in Cs3Lu2Br9, were synthesized by means of the Bridgman technique9−11 or improved Meyer method.12 In order to prepare the alkali metal bromide/rare-earth metal bromide © XXXX American Chemical Society

compounds by phase equilibrium method and acquire the solubility of cesium bromide and rare-earth bromide at 298.15 K in H2O or HBr (∼12 mass %)−H2O medium, the phase equilibria for CsBr + REBr3 + H2O (RE = La, Ce, Pr, Nd, Sm, Er, and Tm) ternary systems and CsBr + REBr3 + HBr (∼13%) + H2O (RE = La, Ce, Pr, Nd, Sm, Dy, Er, and Tm) quaternary systems were reported continuously,13−22 and the related research on rare-earth halide in aqueous media was compiled exhaustively.23 These phase diagrams were highly valuable for researchers to learn the phase equilibrium relationship of CsBr Received: March 18, 2016 Accepted: August 29, 2016

A

DOI: 10.1021/acs.jced.6b00242 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Sample Information

a

chemical

source

CsBr hydrobromic acid Eu2O3 EuBr3·6H2O 5CsBr·2EuBr3·20H2O

Sinopharm Chemical Reagent Co., Ltd. Luoyang Haohua Chemical Reagent Co., Ltd. Sinopharm Chemical Reagent Co., Ltd. synthesis synthesis

mole fraction purity

purification method

0.995a

none none none recrystallization none

0.9999

final mole fraction purity

analysis method

guaranteed reagenta 0.997 0.994b

titration titration

As stated by the supplier. bEvaluated by averaging based on the measured contents of CsBr and EuBr3

K. On the first 1−2 days, the acidity of the liquid phase may deviate from 12 mass % as the result of the gradual establishment of equilibrium and then was adjusted to this concentration. The process was repeated until the HBr mass percentage in liquid phase was kept at about 12 mass %. Subsequently, the samples were sealed again and continuously agitated for another 2−3 days until the new equilibrium was reached. As we all know, in the equilibrium liquid phases of the CsBr + EuBr3 + HBr + H2O quaternary system, it is very difficult to maintain the concentration of HBr at a constant value on the cross-section. So we could only get an average value via the experiment. In the present work we only gave a cross-section result of the CsBr + EuBr3 + HBr + H2O quaternary system at an average concentration of 12.3 mass % HBr. After the systems reached equilibrium, the liquid phases and wet residues were weighed and transferred into a 100 mL volumetric flask, and then, these samples were analyzed by the following method: the content of protons was measured by titration with NaOH solution; the Er3+ concentration was measured by EDTA complexometric titration, the content of Cs+ was analyzed using the gravimetry methods with CsB(C6H5)4 precipitation, and the concentration of Br− was measured by means of titration with the standard solution of AgNO3.24 Schreinemakers technique was used to confirm the solid phases.25 2.3. Equipment. TG-DTG measurements were performed on a NETZSCH STA449C thermal analysis apparatus at 30 cm3·min−1 nitrogen flow and 10 K·min−1 heating rate. XRD determination was undertaken using D/Max-3C diffractometer with Cu Kα radiation source. Excitation and emission spectra were acquired by fluorescence spectrophotometer (Hitachi Model F-7000). The emission spectrum was obtained in a scanning window between 250 and 900 nm with a scanning rate of 12000 nm·min−1. Both excitation and emission slits are 5.0 nm with excitation voltage of 700 V. 2.4. Calorimetric Method. Enthalpy of solution for 5CsBr· 2EuBr3·20H2O was obtained by RD496-2000 microcalorimeter.26 The whole dissolution process needed 0.20 h, and no solid residues were found after the dissolution. For testing of the reliability of the microcalorimeter, the enthalpy of solution for KCl (mass fraction ≥ 0.9999) sample was measured, and the value 17.59 ± 0.10 kJ/mol is consistent with the value previously reported 17.524 ± 0.028 kJ/mol.27 The results proved that the enthalpy of solution data measured by the apparatus was dependable.

and REBr3 in aqueous systems. In the five ternary systems, 2CsBr·REBr3·10H2O (2:1 type) (RE = La, Ce, Pr, Nd, and Sm) were confirmed. In CsBr + REBr3 + HBr (∼13%) + H2O (RE = La, Ce, Pr, Nd, and Sm) quaternary systems, solid-phase compounds 5CsBr·2REBr·22H2O (RE = La, Ce, Pr, Nd, and Sm) (5:2 type) were obtained, in the case of the CsBr + DyBr3 + HBr(∼13%) + H2O system and 5CsBr·3DyBr3·24H2O (5:3 type) was affirmed, but in CsBr + REBr3 + HBr (∼13%) + H2O (RE = Er and Tm) quaternary systems, solid-phase compounds 3CsBr·2REBr3·16H2O (RE = Er, Tm) (3:2 type) were confirmed. The spectroscopy properties of 2CsBr·REBr3· 10H2O (RE = Ce, Pr, Nd, and Sm) and 3CsBr·2REBr3· 16H2O (RE = Er and Tm) indicate that all of them showed upconversion luminescence when they were excited in nearinfrared. This work is the extension of the studies above; it reports the solubility and phase diagrams of systems CsBr + EuBr3 + H2O and CsBr + EuBr3 + HBr (∼12.3%) + H2O at 298.15 K and the thermodynamic characteristics and fluorescence properties of 5CsBr·2EuBr3·20H2O established in the systems.

2. EXPERIMENTAL SECTION 2.1. Reagents. Doubly deionized water (resistivity = 5.7 MΩ·cm) was employed in this experiment. The materials used in the experiment and their corresponding purities are summarized in Table 1. EuBr3·6H2O was obtained by the reaction of Eu2O3 with hydrobromic acid. The sample was recrystallized repeatedly in anhydrous ether and then in water. The compositions of dried compound were measured by analyzing the content of Br− with titration method; then through the titration with EDTA, the Eu3+ content was measured. The molar ratio of EuBr3 to H2O was 1:5.97. The relative errors were less than ±0.22%. 2.2. Experimental Methods and Analysis. The solubility of the CsBr + EuBr3 + H2O system was investigated according to ref 13. The starting materials of CsBr, EuBr3·5.97H2O, and H2O were mixed at different mass ratios. Every sample including liquid and solid phases was sealed and put in a constant temperature water tank equipped with a stirrer. The temperature was fixed at 298.15 K with a precision of ±0.1 K. And the phase equilibrium for CsBr + EuBr3 + H2O system can be reached in about 2 days. For the investigation of the solubility of the CsBr + EuBr3 + HBr (∼12.3%) + H2O system, the experimental method has been described in detail in ref 16. First, different samples were assigned on the phase diagram cross-section with 12 mass % of the liquid phase for HBr. The starting materials of CsBr, EuBr3· 5.97H2O, H2O, and 40 mass % hydrobromic acid were mixed and sealed in a plastic tube. The acidity (HBr mass %) of the liquid phase was kept at 12 mass % HBr for each sample. And then, all the sealed samples were placed in a constant temperature water tank. The temperature was fixed at 298.15

3. RESULTS AND DISCUSSION 3.1. CsBr + EuBr3 + H2O Ternary System at 298.15 K. The phase equilibria experimental data of solubility and the corresponding wet residue of the CsBr + EuBr3 + H2O system at 298.15 K are given in Table 2. The ion concentration of B



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20H2O (5:2 type), and EuBr3·6H2O, respectively. The crystallization field of EuBr3·6H2O is smaller than that of CsBr. The new solid-phase compound 5CsBr·2EuBr3·20H2O is incongruently soluble in water, and it has not been reported in a previous work so far. Based on the phase region where 5CsBr· 2EuBr3·20H2O is in the CsBr + EuBr3 + H2O system, different ratio mixtures of CsBr, EuBr3·6H2O, and H2O were agitated at 298.15 K. After the equilibrium was reached, the solid 5CsBr· 2EuBr3·20H2O was collected by suction filtration method. The composition of 5CsBr·2EuBr3·20H2O are 47.98% CsBr and 35.39% EuBr3 (theoretical data: 48.20% CsBr; 35.48% EuBr3) by chemical analyses. The solubility value of CsBr in this work is in good accord with the reference data 55.23%.28 But the solubility values of EuBr3 are slightly lower than that from the literature with EuBr3 of 64.70%.29 The literature data seem to be distinctly overestimated.23,30 From the comparison of the present ternary system with the reported ternary systems,13,14,21,22 the phase chemical reactions of the five systems CsBr + REBr3 + H2O (RE = La, Ce, Pr, Nd, and Sm) are similar in that they all have compounds 2CsBr· REBr3·10H2O (2:1 type). The compounds 3CsBr·2REBr3· 16H2O (3:2 type) were formed in CsBr + REBr3 + H2O (RE = Er and Tm) systems, so the phase chemical reactions of the two systems are analogous. But the present ternary system is different from the above seven systems reported. 3.2. CsBr + EuBr3 + HBr (∼12.3%) + H2O Quaternary System at 298.15 K. Table 3 shows the solubility for the quaternary system of CsBr + EuBr3 + HBr (∼12.3%) + H2O and the central projection data on the trigonal basal face for the CsBr + EuBr3 + H2O system at 298.15 K. The ion concentration of equilibrium liquid phase and the wet residue are shown as mass percent. Figure 2 displays the corresponding phase diagram. As shown in Figure 2, the solubility curve is composed of three sections in quaternary system of CsBr + EuBr3 + HBr (∼12.3%) + H2O, corresponding to CsBr, 5CsBr·2EuBr3· 20H2O and EuBr3·6H2O, respectively. It demonstrates that the phase field of new compound 5CsBr·2EuBr3·20H2O is formed besides original compounds CsBr and EuBr3·6H2O in this system, and it is incongruently soluble in the medium of ∼12.3% HBr. Composition of 5CsBr·2EuBr3·20H2O was further confirmed by chemical analyses. And the results show that there are 48.31% CsBr (theoretical, 48.20%) and 35.33% EuBr3 (theoretical, 35.48%) for the compound 5CsBr·2EuBr3· 20H2O. The comparison of the two phase diagrams for the ternary system CsBr + EuBr3 + H2O and quaternary system CsBr + EuBr3 + HBr (∼12.3%) + H2O at 298.15 K is shown in Figure 3. It was found that (1) increasing the content of HBr in equilibrium liquid phase, the invariant points move upward from points E1, E2 to F1, F2, respectively. (2) The saturation curves move upward from ME1, E1E2 and E2N to HF1, F1F2 and F2K, respectively, because the solubilities of CsBr, 5CsBr· 2EuBr3·20H2O, and EuBr3·6H2O decrease with increasing the content of HBr. (3) The crystallization region of CsBr in the quaternary system is smaller than that in the ternary system, but the crystallization regions of 5CsBr·2EuBr3·20H2O and EuBr3· 6H2O change a little. Moreover, the phase chemical reactions of the present quaternary system are similar to those of the CsBr + REBr3 + HBr (∼13%) + H2O (RE = La, Ce, Pr, Nd, and Sm) quaternary systems.15−19 The compounds 5CsBr·2REBr·nH2O (5:2 type)

Table 2. Solubility (Mass Percent) of CsBr + EuBr3 + H2O System at Temperature T = 298.15 K and Pressure p = 0.1 MPaa composition of saturated solution/100wb

wet residue/100w

no.

CsBr

EuBr3

CsBr

EuBr3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

55.43 47.36 40.38 31.58 22.10 18.50 17.05 16.66 12.67 9.68 6.84 6.37 6.29 6.03 6.36 6.15 5.59 0.00

0.00 7.76 14.53 23.83 36.62 42.21 46.19 48.11 53.32 56.29 60.20 60.87 61.00 61.14 61.00 61.28 61.03 64.08

95.99 94.91 93.56 89.27 89.99 87.01 54.81 43.99 41.95 38.77 39.87 31.79 26.99 13.58 7.48 1.55

0.66 1.53 2.45 5.30 5.21 7.04 30.59 37.29 38.88 41.03 40.87 47.01 51.52 64.46 69.83 74.47

solid phasec A A A A A A A A+ B B B B B+ B+ B+ B+ C C

B

C C C C

a

Standard uncertainties: u(T) = 0.1 K; u(p) = 5 kPa. Expanded uncertainties U(w) (mass fraction) for CsBr and EuBr3 are 0.003 and 0.0015, respectively (0.95 level of confidence). bDouble saturation point (average). E1: CsBr, 16.66%; EuBr3, 48.11%. E2: CsBr, 6.21%; EuBr3, 61.10%. cCompounds: A, CsBr; B, 5CsBr·2EuBr3·20H2O; C, EuBr3·6H2O.

equilibrium liquid phase and wet residue are expressed as mass percent. On the basis of the measured data, the corresponding phase diagram is presented in Figure 1. In Figure 1, M and N stand for the equilibrium solubility of CsBr and EuBr3 in water at 298.15 K corresponding to 55.43% and 64.08% (mass percent), respectively; E1 and E2 are invariant points. The ME1, E1E2, and E2N are saturation curves, corresponding to the solid phase of CsBr, 5CsBr·2EuBr3·

Figure 1. Phase diagram of the CsBr + EuBr3 + H2O system at 298.15 K. E1 and E2 stand for double saturation points. B and C stand for 5CsBr·2EuBr3·20H2O and EuBr3·6H2O, respectively. C



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Table 3. Solubility (Mass Percent) for the Quaternary System of CsBr + EuBr3 + HBr (12.3%) + H2O at Temperature T = 298.15 K and Pressure p = 0.1 MPa and the Central Projection Data on Trigonal Basal Face CsBr + EuBr3 + H2Oa for w(HBr) = ∼12.34 mass % composition of saturated solution/100w composition in tetrahedralb

composition of wet residue/100w

composition in trigonal basal face

composition in tetrahedral

composition in trigonal basal face

no.

HBr

CsBr

EuBr3

CsBr

EuBr3

HBr

CsBr

EuBr3

CsBr

EuBr3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 170 18 19

12.46 12.52 11.92 12.23 12.46 12.42 12.09 13.18 13.15 13.20 13.04 12.91 12.84 12.62 12.12 11.46 10.89 11.44 11.61

36.77 26.33 19.54 17.76 16.55 14.66 15.52 15.05 12.17 8.88 7.40 7.02 7.25 6.89 7.33 7.07 5.48 2.23 0.00

0.00 11.48 21.98 27.33 30.51 33.16 33.88 33.30 37.45 41.48 42.91 44.92 44.92 45.03 45.39 46.39 46.75 48.79 50.39

42.00 30.09 22.18 20.23 18.90 16.73 17.65 17.33 14.01 10.23 8.50 8.06 8.32 7.88 8.34 7.98 6.14 2.52 0.00

0.00 13.16 24.95 31.13 34.85 37.86 38.53 38.35 43.12 48.18 49.34 51.58 51.54 51.53 51.64 52.39 52.46 55.10 57.00

1.54 1.58 2.32 1.75 2.54 2.92 2.57 3.06 3.54 2.56 2.44 3.39 2.15 2.31 1.92 2.34 2.19

91.17 89.43 84.74 87.86 82.85 47.31 45.19 40.84 38.58 41.61 43.29 37.48 33.36 28.17 21.03 0.94 0.53

1.31 2.81 4.88 4.03 6.52 30.29 33.70 36.24 37.26 35.95 36.27 38.84 44.01 49.07 55.91 72.37 72.58

92.59 90.86 86.75 89.42 85.00 48.73 46.38 42.13 40.00 42.70 44.38 38.79 34.09 28.83 21.44 0.96 0.54

1.33 2.85 4.99 4.10 6.68 31.20 34.59 37.39 38.62 36.89 37.17 40.20 44.97 50.23 57.00 74.10 74.20

solid phasec A A A A A A A+ A+ B B B B B+ B+ B+ B+ C C C

B B

C C C C

a Standard uncertainties: u(T) = 0.1 K, u(p) = 5 kPa. Expanded uncertainties U(w) (in mass fraction) for HBr, CsBr and EuBr3 is 0.002, 0.004 and 0.0015, respectively (0.95 level of confidence). bDouble saturation point (average): E1: HBr 12.63%, CsBr 15.28%, EuBr3 33.59%; E2: HBr 12.26%, CsBr 7.13%, ErBr3 45.43%. cCompounds: A, CsBr; B, 5CsBr·2EuBr3·20H2O; C, EuBr3·6H2O.

Figure 3. Phase diagram for ternary system CsBr + EuBr3 + H2O and quaternary system CsBr + EuBr3 + HBr (∼12.3%) + H2O projected on CsBr + EuBr3 + H2O at 298.15 K: ●, ternary system; ■, quaternary system; E1 and E2, cosaturated points of the ternary system; F1 and F2, cosaturated points of the quaternary system.

Figure 2. Phase diagram for the CsBr + EuBr3 + HBr (∼12.3%) + H2O quaternary system projected on CsBr + EuBr3 + H2O at 298.15 K. F1 and F2 denote double saturation points. B and C stand for 5CsBr·2EuBr3·20H2O and EuBr3·6H2O, respectively.

were formed in CsBr + REBr3 + HBr (∼13%) + H2O (RE = La, Ce, Pr, Nd, Sm, and Eu) systems. But the phase chemical behaviors of the present quaternary system are different from those of the CsBr + REBr3 + HBr (∼13%) + H2O (RE = Dy, Er, and Tm) quaternary systems.20−22 5CsBr·3DyBr·24H2O (5:3 type) was verified in the CsBr + DyBr3 + HBr (∼13%) + H2O system; however, the 3:2 type compound 3CsBr·2REBr3· 16H2O was obtained in the systems CsBr + REBr3 + HBr (∼12.3%) + H2O (RE = Er, Tm).

3.3. XRD Spectra and TG-DTG for Compound 5CsBr· 2EuBr3·20H2O. Figure 4 shows a comparison of XRD spectra for CsBr, 5CsBr·2EuBr3·20H2O, and EuBr3·6H2O. The XRD diffraction pattern for 5CsBr·2EuBr3·20H2O is significantly different from those of CsBr and EuBr 3 ·6H 2 O. This demonstrates that the compound 5CsBr·2EuBr3·20H2O is formed from the reaction between CsBr and EuBr3. D



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The molar enthalpy of formation for 5CsBr·2EuBr3·20H2O was calculated; the equation is as follows: Δf Hm⊖(5CsBr·2EuBr3· 20H 2O(s)) = 5Δf Hm⊖(Cs+(aq)) + 2Δf Hm⊖(Eu 3 +(aq)) + 11Δf Hm⊖(Br−(aq)) + 20Δf Hm⊖(H 2O(l)) − Δsol Hm⊖(5CsBr·2EuBr3· 20H 2O(s))

The standard molar enthalpies of formation for Cs+, Eu3+, and Br− from NBS tables31 are −(258.28 ± 0.50), −(605.0 ± 0.5), and −(121.55 ± 0.10) kJ/mol, respectively. The value of H2O is −(285.83 ± 0.042) kJ/mol taken from CODATA Key Values.32 Based on the schemes above, the standard molar enthalpy of formation for 5CsBr·2EuBr3·20H2O is determined to be −(9659.7 ± 1.6) kJ/mol. 3.5. Upconversion Fluorescence of 5CsBr·2EuBr3· 20H2O. The upconversion emission spectrum of 5CsBr· 2EuBr3·20H2O was monitored in the scanning window from 450 to 900 nm with excitation spectrum in the range of 550− 900 nm. Figure 6 shows the corresponding excitation spectrum

Figure 4. X-ray powder diffraction spectrum for 5CsBr·2EuBr3· 20H2O: (a) 5CsBr·2EuBr3·20H2O, (b) CsBr, and (c) EuBr3·6H2O.

TG-DTG curves of 5CsBr·2EuBr3·20H2O (Figure 5) indicate two obvious dehydration steps in the range of 336 to

Figure 6. Excitation spectra of 5CsBr·2EuBr3·20H2O. “ex” denotes excitation.

Figure 5. TG-DTG curves of 5CsBr·2EuBr3·20H2O.

emitted at 785 nm. When excited by the illumination of 785 nm, the emission spectrum for 5CsBr·2EuBr3·20H2O exhibits at 525 nm (Figure 7). It indicates that the compound 5CsBr· 2EuBr3·20H2O exhibited pure green upconversion lumminescence under 785 nm excitation. This is an anti-Stokes phenomenon. The host material transforms long-wavelength pump sources into short-wavelength emission. The upconversion material has potential applications in laser materials,

463 K. The experimental mass-loss value is 16.78%, which is in good accord with the theoretical dehydration value (16.32%). 3.4. Calorimetry Measurement and Standard Molar Enthalpy of Formation for 5CsBr·2EuBr3·20H2O. Table 4 shows the result of the calorimetric measurement in the limit of infinite dilution. The ΔsolH⊖ m of 5CsBr·2EuBr3·20H2O(s) is 104.69 ± 0.88 kJ/mol in 4.00 cm3 of water at 298.15 K. Table 4. Molar Enthalpies of Solution for 5CsBr·2EuBr3· 20H2O in Deionized Water as a Function of Temperature T = 298.15 K, Mass of Sample m, Enthalpy of Solution Qs, and Molar Enthalpy of Solution ΔsolH⊖ m , at Pressure p = 0.1 MPaa no. 1 2 3 4 5 meanb

M/mg

Qs/mJ

45.58 43.24 45.67 43.24 45.08

2158.2 2066.5 2179.3 2036.6 2125.5

ΔsolH⊖ m /(kJ/mol) 104.53 105.51 105.35 103.98 104.09 104.69 ± 0.88

a

In each experiment, 4.00 cm3 of water was used. Standard uncertainties: u(T) = 0.01 K and u(p) = 5 kPa. bThe level of confidence of U(ΔsolH⊖ m ) is specified to be 0.95.

Figure 7. Upconversion luminescence spectra for 5CsBr·2EuBr3· 20H2O (λex = 785 nm). “em” denotes emission. E



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biological labeling, optical fiber, lighting materials, and flat panel displays.

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4. CONCLUSION The equilibria of the two systems of CsBr + EuBr3 + H2O and CsBr + EuBr3 + HBr (∼12.3%) + H2O at 298.15 K and atmospheric pressure were obtained; the related phase diagrams were plotted. In the ternary and quaternary phase diagrams, there were two invariant points, three saturated liquid curves, and three crystallization fields corresponding to CsBr, 5CsBr· 2EuBr3·20H2O, and EuBr3·6H2O. The new solid-phase compound 5CsBr·2EuBr3·20H2O was incongruently soluble in water or ∼12.3% HBr, and it has not been reported in a previous work so far. The content of EuBr3 in two invariant points decreased as the content of HBr in equilibrium liquid phase increased and that of CsBr changed a little, and the crystallization field of CsBr decreased, but the crystallization regions of 5CsBr·2EuBr3·20H2O and EuBr3·6H2O changed a little. The standard molar enthalpy of solution of 5CsBr·2EuBr3· 20H2O was measured in the limit of infinite dilution; its standard molar enthalpy of formation was obtained by calculation. The fluorescence excitation and emission spectra for 5CsBr· 2EuBr3·20H2O were obtained, and the results indicate that the compound has upconversion fluorescence property. All results obtained from this experiment can be used for the rare-earth industry and future theoretical studies.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.:+86 0377 63513540. Fax: +86 0377 63513540. Funding

This work was supported by the National Natural Science Foundation of China (Grant No. 21173123). Notes

The authors declare no competing financial interest.

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REFERENCES

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(Solid + Liquid) Phase Equilibria for the Systems CsBr + EuBr3 + H2O

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