Solvent LiCl–KCl in the nephelauxetic series for trivalent rare earths

Abstract

The spectra of trivalent Ce, Pr, Nd, Sm, Eu, Tb, Dy, Tm, and Yb ions in molten LiCI-KC1 at 450 "C are reported over the range 0.28 to 2.8 ~r, and the baricenters of terms are tabulated for a wide variety of crystal and liquid hosts. These hosts can be arranged in a nephelauxetic series and for Pr3+ actual nephelauxetic parameters, (3, can be calculated by comparing average multiplet energies.Canadian Journal of Chemistry, 46, 3457 (1968) The region of optical transparency for fused salt media can extend quite far into the infrared. For instance, the limiting wavelengths are 2.6 p for LiN03-KNO, eutectic at 150 "C (I), 2.8 p for LiC1-KC1 eutectic at 450 "C (2), and 2.7. p for a ternary sulfate at 550 "C compared with 1.4 p for water at 25 "C. This is useful for the study of lanthanide ions since their 4f" bands in this region are less subject to the complications of overlapping multiplets. Pm3+ in LiC1-KC1 eutectic at 400 "C through the visible and near infrared regions to 1 p. Sm3+ and Pr3+ ions have been investigated in LiC1-KC1 eutectic with high resolution in the near infrared (2), while several ions were studied in LiCl-KC1-NaCI eutectic at 400 "C (4). Carnall and co-workers (5-7) discussed the spectra of all the trivalent lanthanides except La3 + and Ce3 + in LiN0,-KN03 eutectic in terms of the transitions between LS multiplets of 4f". Certain ions were studied from an analytical viewpoint in fluoride melts by Young and White (8,9) and the spectrum of Nd3+ in LiCl-KC1 and LiF was used to illustrate the use of the Unicam S.P. 700 spectrophotometer (10). The characteristic narrow bands of these ions appeared in all melts but some fine structure was lost. Bands obtained only in nitrate melts in the 1.7 p region were ascribed to water contamination (4). A temperature increase of 400 "C caused a bathochromic shift of the Ho3 + bands (4) but a 200 "C increase showed no effect on the Nd3+ bands (10). This paper reports the spectra of several trivalent lanthanides in LiCl-KC1 eutectic a t 450 "C over the range 0.28 to 2.8 p. Comparisons are made with the spectra in other solvents and crystals and actual or relative nephelauxetic parameters are evaluated for the 4f electrons. A discussion of the nephelauxetic effect in rare earths appears in Sinha's book (11) together with other tables of spectra. Experimental Preparation of Lauthanide Ion Sol~~tior~s in LiCI-KC1E~rtectic Pure anhydrous eutectic was prepared by a procedure essentially following Laitinen, Tischer, and R o e (12). SmCI, was prepared by passing HCI over hydrated chloride (Johnson Matthey Ltd., London) in a silica boat while raising the temperature to 550 "C over a period of 30 h. YbCI, was purified by sublin~ation of so-called anhydrous material (Koch Light Laboratories) a t 600 OC, 5 x r on to a water-cooled finger; the raw material was 3 % deficient in chlorine and gave turbid solutions in the melt. Thcse two salts could be added directly to the solvent. The hydrated chloride or oxides of the other ions (Johnson Matthey Ltd., Koch Light) were adde...

Optical absorption and fluorescence properties of trivalent lanthanide chlorides in high temperature molten LiCl–KCl eutectic

“…The measured molar absorptivity at 407 nm was 2.48 70.10 M À 1 cm À 1 , and it was very comparable with a reported value of 2.65 M À 1 cm À 1 in literature at 400°C [11]. In literatures [16,18], the absorption bands of Sm(III) were observed in the near infrared (NIR) region. However, recording the spectrum in NIR region was limited with a measurement restriction of the equipment used in this work.…”

“…The spectrum is very comparable with that measured in literature studies at 400°C [11] and 450°C [18]. The molar absorptivity was not derived by calibration curve and was calculated with the spectra measured at one single Yb(III) concentration using Eq.…”

“…The strong and broad absorption band of Ce(III) centered around 320 nm has been described in LiCl-KCl eutectic at 450°C and 500°C [18,28] and the weak band centered at 263 nm has not been reported in LiCl-KCl eutectic [11,18,28]. However, the absorption spectra of both bands ascribed to 4f-5d transitions were clearly observed in the present study, as shown in Fig.…”

“…For that reason, a few experimental works have been performed by using spectroscopic techniques in the molten halide salts. The absorption spectroscopic properties of most lanthanides in various molten halide salts have been analyzed to investigate the structural symmetry of chemical constitution and redox behaviors and to determine their molar absorptivities for the purpose of quantification [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. However, the absorption spectra and the molar absorptivities in those literature works have not been completely reported for all lanthanide series.…”

Structural investigation of the Tb(III)–Ln(III) (Ln=Nd, Sm) binary system in molten LiCl–KCl eutectic salt by fluorescence resonance energy transfer

“…The absorption spectroscopic properties of most lanthanide elements have been reported in molten chloride salts at high temperatures. The structural symmetry of chemical compounds and their redox behaviors in molten salt have been analyzed [11][12][13][14][15][16][17][18][19][20][21][22]. The structure of molten LnCl 3 in XCl (Ln¼lanthanide, X¼alkali metal) molten salts has been identified as the octahedral structure of Lncl 3 À 6 from Raman spectroscopy [12,[23][24][25][26].…”