Solid + Liquid Equilibria for the Systems CsBr + ErBr3 + H2O and CsBr

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Solid + Liquid Equilibria for the Systems CsBr + ErBr3 + H2O and CsBr + ErBr3 + HBr (∼12.3%) + H2O at 298.15 K and Atmospheric Pressure and Thermodynamic and Fluorescent Properties of the New SolidPhase Compound Zhao-Wan Li, Zhan-Ping Qiao,* Yuan-Lin Dang, Xin Chen, and Qi-Chao Yang College of Chemistry and Pharmacy Engineering, Nanyang Normal University, Nanyang 473061, P. R. China ABSTRACT: The phase equilibria of the ternary system CsBr + ErBr3 + H2O and the quaternary system CsBr + ErBr3 + HBr (∼12.3 %) + H2O at 298.15 K were determined experimentally with the isothermal solubility method. Based on the measured solubility data, the corresponding phase diagrams were plotted. In the ternary system, three crystallization regions corresponding to CsBr, 3CsBr·2ErBr3·16H2O, and ErBr3·9H2O were found. Similarly, there were three crystallization regions corresponding to CsBr, 3CsBr·2ErBr3·16H2O, and ErBr3· 7H2O in the quaternary system. The phase diagrams of the ternary and quaternary systems were compared, and it showed that (1) a new double salt 3CsBr·2ErBr3·16H2O was formed which was incongruently soluble in the two systems; (2) the area of the crystallization region of 3CsBr·2ErBr3·16H2O increased with the increasing concentration of HBr in the equilibrium liquid phase, and (3) ErBr3·9H2O transformed into ErBr3·7H2O when the HBr reached a certain amount. The new solid-phase compound 3CsBr·2ErBr3·16H2O was characterized by chemical analysis, XRD, and TG-DTG techniques. The standard molar enthalpy of solution of 3CsBr·2ErBr3·16H2O in water was confirmed to be −(6.69 ± 0.29) kJ·mol−1 by microcalorimetry in the limit of infinite dilution and its standard molar enthalpy of formation was determined to be −(7846.1 ± 1.2) kJ·mol−1. The fluorescence excitation and emission spectra of 3CsBr·2ErBr3·16H2O were measured. The results indicated that up-conversion spectra of the new solid phase compound exhibit at 470 nm and are excited at 710 nm.

1. INTRODUCTION The rare earth elements, possessing versatility and specificity, have wide application prospects in biology, medical diagnosis, sensing, photovoltaic cells, solar energy conversion, hydrogen fuel storage, trichromatic fluorescent lamps, and other fields.1−5 Thermodynamic properties of their compounds play very important roles in scientific research and industrial applications. So it is certainly necessary to search, find, and characterize the basic thermodynamic properties of the compounds containing lanthanides. The synthesis of the compounds of the alkali metal bromide/ rare-earth metal bromide by phase equilibrium method has been reported continuously, such as REBr3 + CsBr (RE = La, Ce, Pr, Tb, Dy) binary systems,6−10 CsBr + REBr3 + H2O (RE = La, Ce) ternary systems,11 and CsBr + REBr3 + HBr (∼13 %) + H2O (RE = La, Ce, Pr, Nd, Sm, Dy) quaternary systems.12−17 The related results of rare earth metal halide in aqueous systems were evaluated exhaustively.18 In the binary systems, three types (type means the molar ratio of CsBr to REBr3) new solid-phase compounds were obtained, including Cs3REBr6 (3:1 type) (RE = La, Ce, Pr, Tb, Dy), Cs3RE2Br9 (3:2 type) (RE = Tb, Dy), Cs2REBr5 (2:1 type) (RE = La, Ce), and CsRE2Br7 (1:2 type) (RE = La, Ce, Pr, Tb). In the ternary systems, 2CsBr·REBr3·10H2O (2:1 type) (RE = La, Ce) were © 2015 American Chemical Society

determined. For the quaternary systems CsBr + REBr3 + HBr(∼13 %) + H2O (RE = La, Ce, Pr, Nd, Sm), new solidphase compounds 5CsBr·2REBr·22H2O (RE = La, Ce, Pr, Nd, Sm) (5:2 type) were affirmed, while for the quaternary system CsBr + DyBr3 + HBr(∼13 %) + H2O, solid phase compound 5CsBr·3DyBr3·24H2O (5:3 type) was confirmed. The spectroscopy properties of the 2CsBr·CeBr3·10H2O exhibit upconversion luminescence when being excited in the nearinfrared or visible region. In comparison of the above systems, it can be found that the phase chemical reactions of the two binary systems REBr3 + CsBr (RE = La, Ce) are similar because they all have 3:1, 2:1, and 1:2 type compounds. For the two binary systems REBr3 + CsBr (RE = Tb, Dy), their phase chemical reactions have both similarity (all having 3:1 and 3:2 type compounds) and dissimilarity. Similarly, for the binary systems REBr3 + CsBr (RE = La, Ce) with REBr3 + CsBr (RE = Pr, Tb, Dy), they also have both comparability and dissimilarity. But for ternary systems CsBr + REBr3 + H2O (RE = La, Ce), their phase chemical reactions are similar. As far as the quaternary systems Received: February 13, 2015 Accepted: May 15, 2015 Published: May 20, 2015 1900

DOI: 10.1021/acs.jced.5b00139 J. Chem. Eng. Data 2015, 60, 1900−1905

Journal of Chemical & Engineering Data

Article

run on NETZSCH STA449C thermal analysis apparatus at 30 cm3·min−1 nitrogen flow and 10 K·min−1 heating rate. X-ray diffraction (XRD) determination was carried out by a D/Max3C diffractometer using Cu Kα radiation at room temperature. The excitation and emission spectra of the compounds were recorded on the Hitachi model F-7000 fluorescence spectrophotometer equipped with the Xe lamp. The emission spectra of the compounds were detected when the excitation illuminants is continuously scanning in the range of (250 to 900) nm, the scanning rate is 12000 nm·min−1, and the excitation and emission slits are both 5.0 nm. The excitation voltage was 700v. 2.4. Calorimetric Technique. The value of the enthalpy of solution of 3CsBr·2ErBr3·16H2O was obtained by An RD4962000 heat conduction microcalorimeter (Mianyang CP Thermal Analysis Instrument Co., Ltd., China), which has been described in detail previously.21 The whole dissolution process need for 0.25 h, and no solid residues were observed after the dissolution in each calorimetric experiment. In order to check the behavior of the calorimeter, the enthalpy of solution of KCl (mass fraction ≥ 0.9999) in distilled water was measured to be (17.59 ± 0.10) kJ·mol−1, which was consistent with that of (17.524 ± 0.028) kJ·mol−1 reported in the literature.22 This proved that the device used for measuring the enthalpy of solution in this work was reliable.

CsBr + REBr3 + HBr + H2O are concerned, they belong to the same category when RE is a light rare earth bromide. The present paper is a part of our ongoing extensive program focused on phase equilibrium about CsX−REX3 (X = Cl, Br) in the aqueous systems, about thermodynamic and fluorescent properties of the new solid-phase compound. It reports the solubility and phase diagrams of the CsBr + ErBr3 + H2O and CsBr + ErBr3 + HBr (∼12.3 %) + H2O systems at 298.15 K and the thermodynamic and fluorescent properties of the incongruently soluble 3CsBr·2ErBr3·16H2O compound.

2. EXPERIMENTAL SECTION 2.1. Reagents. All reagents and solvents employed were commercially available and used without further purification. Quartz double deionized water was used (resistivity = 5.7 MΩ· cm). Table 1 summarizes relevant information on sample material purity. Table 1. Chemical Sample Used in This Study reagent CsBr Er2O3 hydrobromic acid

initial mole fraction

source

state

Sinopharm Chemical Reagent Co., Ltd. National Engineering Research Centre of Rare Earth Metallurgy and Function Materials Sinopharm Chemical Reagent Co., Ltd.

solid

0.995

solid

0.9999

liquid

HBr ≥ 0.129 (analytical reagent)

3. RESULTS AND DISCUSSION 3.1. Ternary System of CsBr−ErBr3−H2O at 298.15 K. The solubility data of the ternary system of CsBr−ErBr3−H2O at 298.15 K are tabulated in Table 2. The ion concentration values in the saturated solution and the corresponding wet residue are expressed as mass fraction. Based on the experimental results in Table 2, the phase diagram of the system at 298.15 K is shown in Figure 1. Figure 1 shows that the CsBr−ErBr3−H2O system has two invariant points (E1, E2) and three crystallization zones corresponding to the three equilibrium solid phases CsBr, 3CsBr·2ErBr3·16H2O (3-2-16), and ErBr3·9H2O, respectively. The solid-phase compound 3CsBr·2ErBr3·16H2O is incongruently soluble in water. The chemical analyses indicate that there are 36.79 % CsBr and 46.69 % ErBr3 for 3CsBr·2ErBr3· 16H2O (theoretical data, 36.68 % CsBr, 46.76 % ErBr3). Comparing of the present ternary system with the reported ternary systems,11 the phase chemical reactions of them are dissimilar. The new solid compound 3CsBr·2ErBr3·16H2O of the 3:2 type is formed in the system CsBr−ErBr3−H2O, but the solid compounds 2CsBr·REBr3·10H2O of the 2:1 type (RE = La, Ce) are obtained in the systems CsBr−REBr3−H2O. 3.2. Quaternary System of CsBr + ErBr3 + HBr (∼ 12.3 %) + H2O at 298.15 K. Table 3 shows the solubility data of the quaternary system of CsBr + ErBr3 + HBr (∼ 12.3 %) + H2O and the central projection data on the trigonal basal face of the CsBr + ErBr3 + H2O at 298.15 K. The ion concentration values of the equilibrium liquid phase and wet solid phase are expressed as mass fraction. Figures 2 displays the corresponding phase diagram. The phase diagram of the quaternary system of CsBr + ErBr3 + HBr (∼12.3 %) + H2O presents two invariant points, three crystallization fields corresponding to the three equilibrium solid phases CsBr, 3CsBr·2ErBr3·16H2O, and ErBr3·7H2O, respectively. One new solid-phase compound 3CsBr·2ErBr3· 16H2O (3−2−16) crystallized from the saturated solutions. The compound 3CsBr·2ErBr3·16H2O is incongruently soluble

ErBr3·9H2O was prepared by a reaction of Er2O3 with hydrobromic acid. The sample was repeatedly crystallized with water and repetitively scrubbed with anhydrous ether, then dried in glass desiccator. The compositions were confirmed by analyzing the Br− content by titration with a normal solution of silver nitrate, and through the titration of EDTA, the Er3+ content was measured. The molar ratio of ErBr3 to H2O was 1:8.95. The purity reached this way was found to be 99.8 %. The relative errors were less than ± 0.22 %. 2.2. Investigations on the System at 298.15 K and Analysis Methods. The solubilities of the systems of CsBr + ErBr3 + H2O and CsBr + ErBr3 + HBr(∼12.3 %) + H2O were investigated according to ref 19. The starting materials of CsBr, ErBr3·8.95H2O, and H2O for the ternary system, and CsBr, ErBr3·8.95H2O, H2O, and hydrobromic acid for the quaternary system were mixed in different mass ratios. Each sample containing solid and liquid phase was sealed in a plastic container, and all of the sealed samples were put in a constanttemperature water tank controlled by the electrical stirrer. The temperature was fixed at 298.15 K with a precision of ± 0.1 K. The phase equilibrium of the systems of CsBr + ErBr3 + H2O and CsBr + ErBr3 + HBr (∼ 12.3 %) + H2O can be reached in about 3 days and 5 days, respectively. The concentration of protons was analyzed by titration with a solution of sodium hydroxide, the Er3+ concentration was determined by EDTA complexometric titration, the concentration of the Cs+ was analyzed by the gravimetry methods with the precipitation of CsB(C6H5)4 and the concentration of Br− was measured by titration with a normal solution of silver nitrate. The solid phases formed in the studied system were confirmed by Schreinemakers’ method of wet residues.20 2.3. Equipment and Conditions. Thermogravimetric/ differential thermogravimetric (TG-DTG) measurements were 1901



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coincide with theoretical data (22.90 % Cs, 19.21 % Er, and 41.31 % Br) very well. In comparison of Figure 1 with Figure 2, it was found that (1) the phase region of compound ErBr3·9H2O transforms into ErBr3·7H2O when the added HBr reaches a certain amount; (2) the crystallization field of 3CsBr·2ErBr3·16H2O increases, and the solubility of all the compounds decreases with increasing the concentration of HBr in the equilibrium liquid phase. In addition, the phase chemical reactions of the present quaternary system were dissimilar to those of the systems CsBr + REBr3 + HBr (∼13 %) + H2O (RE = La, Ce, Pr, Nd, Sm, Dy) quaternary systems.12−17 The new solid compounds 5CsBr· 2REBr·22H2O (RE = La, Ce, Pr, Nd, Sm) (5:2 type) were formed in the systems CsBr + REBr3 + HBr (∼13 %) + H2O (RE = La, Ce, Pr, Nd, Sm), and solid phase compound 5CsBr· 3DyBr·24H2O (5:3 type) was confirmed in the system CsBr + DyBr3 + HBr (∼13 %) + H2O; however, the 3:2 type compound 3CsBr·2ErBr3·16H2O was obtained in the system CsBr + ErBr3 + HBr (∼12.3 %) + H2O. The results show that ErBr3 exhibits some differences from LaBr3, CeBr3, PrBr3, NdBr3, SmBr3, and DyBr3 with CsBr in its phase chemical behavior. 3.3. XRD and TG−DTG of New Solid Phase Compound 3CsBr·2ErBr3·16H2O. Figure 3 displays the X-ray diffraction spectra of 3CsBr·2ErBr3·16H2O. The XRD diffraction pattern for 3CsBr·2ErBr3·16H2O is obviously much different from those of CsBr and ErBr3·7H2O. This demonstrates that the three compounds are formed from a reaction between CsBr and ErBr3. TG-DTG curves of 3CsBr·2ErBr3·16H2O (Figure 4) indicate four obvious dehydration steps over a temperature range from (341 to 523) K. The experimental mass-loss value (16.71 %) is well agreement with calculation data (16.56 %). 3.4. Calorimetry and Standard Molar Enthalpy of Formation of 3CsBr·2ErBr3·16H2O. The molar enthalpy of solution of ΔsolHθm of 3CsBr·2ErBr3·16H2O (s) is − (6.69 ± 0.29) kJ·mol−1 in 4.00 cm3 of water at 298.15 K. The values are listed in Table 4, in which m is the mass of sample, ΔsolHθm is the molar enthalpy of solution of sample. The Standard uncertainties u are u(ΔsolHθm) = ± 2.78s/n1/2, in which s is standard deviation, n is the number of experimental measurements. A 0.95 level of confidence is used. The molar enthalpy of formation of 3CsBr·2ErBr3·16H2O can be calculated according to the following equation:

Table 2. Solubility Data, in Mass Fraction, for the Ternary System CsBr−ErBr3−H2O at T = 298.15 K and p = 0.1 MPaa composition of saturated solution /w %b

composition of wet residue/w %

no.

CsBr

ErBr3

CsBr

ErBr3

solid phasec

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

55.51 49.31 42.97 35.68 30.65 25.92 21.76 18.65 17.08 16.09 15.11 14.07 14.20 14.48 14.17 12.24 10.94 10.89 9.83 8.31 7.22 4.39 2.47 0.00

0.00 5.94 11.80 18.95 24.84 30.00 35.36 40.90 44.16 46.59 49.87 54.80 55.56 55.52 55.93 57.44 58.72 58.75 59.89 61.34 61.73 63.38 64.48 65.73

90.84 92.13 88.76 90.49 85.28 87.79 88.42 86.23 87.09 86.12 79.05 79.67 31.85 24.19 24.11 26.14 20.24 22.54 13.78 2.42 1.52 0.45

1.19 1.84 3.47 3.43 6.25 4.88 5.41 7.29 7.20 8.62 12.96 13.17 47.08 51.53 52.40 51.80 54.37 53.76 60.55 68.41 69.28 70.27

A A A A A A A A A A A A A A+B B B B B B B+C C C C C

a

Standard uncertainties u are u(T) = 0.1 K, u(p) = 5 kPa, u(w) for CsBr and ErBr3 are 0.0035 and 0.0016, respectively. bDouble saturation point (average): E1: CsBr, 14.48 %; ErBr3, 55.52 %. E2: CsBr, 8.31 %; ErBr3, 61.34 %. cCompounds: A, CsBr; B, 3CsBr· 2ErBr3·16H2O; C, ErBr3·9H2O.

Δf Hmθ (3CsBr·2ErBr3· 16H 2O)(s) = 3Δf Hmθ (Cs+)(aq) + 2Δf Hmθ (Er 3 +)(aq) + 9Δf Hmθ (Br −)(aq) + 16Δf Hmθ (H 2O)(l) − Δsol Hmθ (3CsBr·2ErBr3· 16H 2O)(s)

The standard molar enthalpies of formation of Cs+, Er3+, and Br taken from the NBS tables23 are −(258.28 ± 0.50) kJ· mol−1, −(705.4 ± 0.5) kJ·mol−1, and −(121.55 ± 0.10) kJ· mol−1, respectively. That of H2O is −(285.83 ± 0.042) kJ· mol−1 taken from the CODATA Key Values.24 Using these schemes above, the standard molar enthalpy of formation of 3CsBr·2ErBr3·16H2O is calculated to be −(7846.1 ± 1.2) kJ· mol−1. 3. 5. Upconversion Fluorescence of 3CsBr·2ErBr3· 16H2O. The upconversion emission spectra of 3CsBr·2ErBr3· 16H2O was monitored in the range from (450 to 900) nm with −

Figure 1. Phase diagram for the ternary system CsBr−ErBr3−H2O at 298.15. E1 and E2 denote double saturation point. B and C stand for 3CsBr·2ErBr3·16H2O and ErBr3·9H2O, respectively.

in the medium of ∼12.3 % HBr. The compound 3CsBr·2ErBr3· 16H2O obtained from the system was analyzed by a titration method. Its composition is Cs (22.80 %), Er (19.28 %), and Br (41.42 %) in 3CsBr·2ErBr3·16H2O. The experimental results 1902



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Table 3. Solubility Data, in Mass Fraction, for the Quaternary System CsBr−ErBr3−HBr(∼ 12.3 %)−H2O T = 298.15 K and p = 0.1 MPaa and Central Projection Data on the Trigonal Basal Face CsBr−ErBr3−H2O composition of solution composition in the tetrahedral/wt %b

composition of residue

composition in the trigonal basal face/wt %

composition in the tetrahedral/wt %

no.

HBr

CsBr

ErBr3

CsBr

ErBr3

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 170 18 19 20

12.46 13.18 13.30 13.35 12.92 13.51 12.84 12.51 12.84 12.73 12.93 12.46 12.91 12.10 10.77 10.35 9.82 11.98 11.86 12.44

36.77 31.68 25.83 20.07 16.17 14.95 15.12 15.53 15.04 15.66 15.86 15.56 14.96 13.06 12.17 8.23 8.01 4.17 2.64 0.00

0.00 4.79 11.94 20.85 30.28 35.60 37.99 39.60 39.52 39.23 39.04 39.62 40.79 42.44 44.83 49.27 49.81 49.47 50.50 51.51

42.00 36.50 29.79 23.17 18.57 17.28 17.35 17.75 17.25 17.95 18.22 17.79 17.18 14.86 13.64 9.19 8.88 4.74 3.00 0.00

w(HBr) = ∼12.3 mass % 0.00 5.52 1.49 92.07 13.78 1.55 92.41 24.06 2.03 89.60 34.77 1.77 88.73 41.16 2.33 86.65 43.58 2.03 87.39 45.26 1.89 86.41 45.34 3.94 57.04 44.95 4.18 49.32 44.84 5.39 38.87 45.25 4.83 37.05 46.84 6.36 28.77 48.28 6.04 28.23 50.24 4.01 26.85 54.96 4.23 27.31 55.23 4.66 20.54 56.21 2.55 1.39 57.29 2.89 0.65 58.83

HBr

CsBr

composition in the trigonal basal face/wt %

ErBr3

CsBr

ErBr3

solid phasec

0.65 1.42 2.83 4.21 5.71 5.55 6.16 25.31 31.25 36.63 38.82 42.34 43.32 46.10 46.88 50.87 69.85 68.53

93.47 93.87 91.45 90.33 88.72 89.20 88.07 59.38 51.48 41.09 38.93 30.72 30.05 27.98 28.52 21.54 1.33 0.67

0.66 1.44 2.89 4.29 5.85 5.66 6.28 26.35 32.62 38.72 40.80 46.22 47.10 48.03 48.95 53.36 71.68 70.57

A A A A A A A A A+B A+B A+B A+B B B B B B+D D D D

a Standard uncertainties u are u(T) = 0.1 K, u(p) = 5 kPa, u(w) for HBr, CsBr, and ErBr3 are 0.0020, 0.0035, and 0.0016, respectively. bDouble saturation point (average): E1: CsBr, 17.80 %; ErBr3, 45.09 %. E2: CsBr, 8.88 %; ErBr3, 55.23 %. cCompounds: A, CsBr; B, 3CsBr·2ErBr3·16H2O; D, ErBr3·7H2O.

Figure 3. X-ray powder diffraction spectrum of 3CsBr·2ErBr3·16H2O.

4. CONCLUSION The solid liquid equilibrium of the ternary system CsBr + ErBr3 + H2O and the quaternary system CsBr + ErBr3 + HBr (∼12.3 %) + H2O at 298.15 K and atmospheric pressure were obtained, and the corresponding phase diagrams were established for the first time in the course of our present work. There were in all two invariant points, three saturated liquid curves, and three crystallization regions in the ternary and the quaternary phase diagrams. The new solid-phase compound 3CsBr·2ErBr3·16H2O was incongruently soluble in water or the medium of ∼12.3 % HBr. The crystallization region of 3CsBr·2ErBr3·16H2O in the quaternary system was

Figure 2. Phase diagram for the quaternary system CsBr−ErBr3− HBr(∼ 12.3 %)−H2O projected on CsBr−ErBr3−H2O at 298.15 K. E1 and E2 denote double saturation point. B and D stand for 3CsBr· 2ErBr3·16H2O and ErBr3·7H2O, respectively.

excitation spectra in the range of (550 to 900) nm. Figure 5 shows corresponding excitation spectra emitted at 710 nm. When excited by the illumination of 710 nm, the emission spectra of the compound exhibits at 470 nm (Figure 6). It indicates that the compound 3CsBr·2ErBr3·16H2O has upconversion luminescence when excited at 710 nm. 1903



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Figure 4. TG-DTG curves of 3CsBr·2ErBr3·16H2O.

Figure 6. Upconversion luminescence spectra of 3CsBr·2ErBr3·16H2O (λex = 710 nm).

Table 4. Molar Enthalpies of Solution of 3CsBr·2ErBr3· 16H2O in Deionized Water at 298.15 Ka no.

M/mg

1 2 3 4 5 meanb

66.11 67.06 63.88 67.07 62.78

Qs/mJ

ΔsolHθm/(kJ·mol−1)

In the ternary system CsCl + ErCl3 + H2O and quaternary system CsCl + ErCl3 + HCl (∼10.7 %, ∼14.4 %) + H2O reported,25 the new solid phase compound 3CsCl·2ErCl3· 14H2O (3:2 type) were obtained both in the ternary and quaternary systems. But 3CsCl·ErCl3·6H2O (3:1 type) were obtained only in the ternary system and nCsCl·ErCl3·6H2O (not-identify solid) only in the quaternary system. Furthermore, a 3:1 type compound disappears in ternary system CsBr + ErBr3 + H2O, and nCsX·ErX3·nH2O cannot exist in the quaternary system CsBr + ErBr3 + HBr (∼ 12.3 %) + H2O. The differences above could be caused by the radius of Br−and Cl−.

−244.7 −6.44 −267.2 −6.93 −256.3 −6.98 −255.1 −6.61 −234.6 −6.50 ΔsolHθm = −(6.69 ± 0.29) kJ·mol−1

a

In each experiment, 4.00 cm3 water was used. bStandard uncertainties u are u(T) = 0.01 K and u(p) = 5 kPa. u(ΔsolHθm) = ± 2.78s/n1/2 (s is standard deviation, n is the number of experimental measurements) (0.95 level of confidence).

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AUTHOR INFORMATION

Corresponding Author

*E-mail address: [email protected] (Z.Q.). Tel.: +86 0377 63513540; fax: +86 0377 63513540. Funding

Acknowledgment is expressed for the financial support from the National Natural Science Foundation of China (No. 21173123). Notes

The authors declare no competing financial interest.

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REFERENCES

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Figure 5. Excitation spectra of 3CsBr·2ErBr3·16H2O (λem = 470 nm).

obviously larger than that in the ternary system. The compound ErBr3·9H2O transformed into ErBr3·7H2O when the added HBr to the solution reached a certain amount. The standard molar enthalpy of solution for the compound 3CsBr·2ErBr3·16H2O was measured in the limit of infinite dilution and its standard molar enthalpy of formation was calculated. The fluorescence excitation and emission spectra of 3CsBr· 2ErBr3·16H2O were measured. The results show that the compound has upconversion fluorescence properties. All results obtained in this experiment can be used for the rare earth industry and future theoretical studies. 1904



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Solid + Liquid Equilibria for the Systems CsBr + ErBr3 + H2O and CsBr

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