Nathan A. Stump

Luminescence Study of the Thermal Decomposition of Europium Trichloride Hexahydrate, EuCl3·6H2O

We have studied the thermal decomposition of EuCl3·6H2O using in situ measurements of the Eu3+ ion luminescence spectrum. The luminescence spectrum proved to be extremely sensitive to structural and compositional changes undergone by the title compound during the decomposition process. There appeared to be no change in the oxidation state of the europium throughout the decomposition process. Four differently hydrated species of EuCl3·nH2O (n = 6, 3, 2, or 1) were identified via luminescence spectroscopy. We also observed another intermediate compound formed from the monohydrate prior to the final product EuOCl. Our analysis of this intermediates spectrum indicates a single Eu3+ ion site, which is consistent with a formulation of Eu(OH)Cl2 rather than a mixed EuOCl·2EuCl3 product, both of which have been postulated by others on the basis of their thermogravimetric measurements.

Temperature Dependence of the Luminescence Lifetime of the Eu3+ Ion in EuCl3

The luminescence spectrum of EuCl3 has been recorded in this laboratory, and the energy levels of the Eu3+ ion in EuCl3 have been assigned. The temperature dependence of the luminescence lifetime of the Eu3+ ion in EuCl3 is dealt with in this communication to shed light on the relaxation mechanism operative in EuCl3.

Photoluminescence and Visible Diffuse-Reflection Spectroscopic Evidence of Samarium Reduction in Air-Fired Samples of Mixed Samarium: Strontium Tetraborate Precipitates

Photoluminescence and visible diffuse-reflection spectroscopies have provided evidence of the reduction of samarium to the divalent state in samarium-doped strontium borate and pure samarium borate samples. The samples were prepared by the air firing of homogeneous precipitates of divalent strontium and trivalent samarium ions from aqueous solutions with saturated sodium tetraborate. The use of this method in the preparation of divalent lanthanide ions has not been reported previously. Reduced samarium was observed in fired tetraborate precipitates prepared with solutions containing 1, 5, 10, 25, 50, 75, and 90 mole percent samarium versus strontium. Divalent samarium also was identified in fired precipitates of trivalent samarium solutions precipitated with tetraborate. Sm2+ was identified as the primary emitting species in each of the eight compositions. However, diffuse-reflection spectroscopy indicated the presence of trivalent samarium in the studied samples, ranging from minimal for samples prepared with low samarium concentrations to nearly exclusive when pure samarium was studied. Quenching of the characteristic emission associated with the trivalent species is believed to result in the absence of the emission features arising from residual samarium(III) in the products. Although the absence of trivalent samarium emission enhanced the ability of emission spectroscopy to identify small amounts of divalent samarium, indicating that reduction had occurred, it limited the ability of this method to determine the extent of the reduction. Diffuse-reflection spectroscopys ability to look at both species provided a much better analysis of the extent of samarium reduction.

Temperature Dependence of the Eu 3+ Ion Luminescence Lifetime Exhibited by Anhydrous EuCl 3

Recently, Chen et al. have discussed the effects of slight variations in temperature on the luminescence lifetime of the Eu3+ ion in anhydrous EuCl3. In that work, the luminescence lifetime exhibited a continuous exponential decrease with a linear increase in temperature. However, a limited number of data points were employed, and the range of temperatures was limited to between 293 and 368 K. Attempts to expand the study of anhydrous EuCl3 to temperatures above 368 K resulted in irreversible alterations in the sample (e.g., chemical reaction with its container or structural phase transition), which precluded studies of the sample at higher temperatures. Investigations of the luminescence lifetime below 293 K had not been carried out previously because it was expected that the exponential trend would continue. This assumption appeared to be well founded, since compositional and/or structural variations in anhydrous EuCl3 have not been reported in this temperature range. We have now determined that the previously established trend has not continued and report here the extended thermal dependence of the Eu3+ ion luminescence lifetime in anhydrous EuCl3, at temperatures below 293 K.

Lanthanide luminescence spectroscopy as a monitor of crystal structure

We wish to address the criticisms of Tanner and Rudowicz regarding the feasibility of using lanthanide luminescence spectroscopy as a monitor of crystal structure, as was suggested in the recent paper by Chen et al. Such optical methods (including absorption and phonon Raman spectroscopy) have been and continue to be employed successfully by the present authors to investigate and characterize f-element solids. The ability to use such methods to recognize structures is a matter of record; to argue their nonfeasibility rejects this past evidence and success.

Luminescence Study of the Samarium(II) Sites in Samarium: Barium Octaborate as Differentiated by Excitation Wavelength and Temperature

Divalent samarium incorporated in a barium octaborate matrix prepared by firing homogeneous precipitates has been studied with emission spectroscopy. One of the samarium sites associated with this product exhibits an extremely strong temperature dependence upon using an excitation wavelength of 532 nm. This effect allows for specific differentiation between the two major Sm(II) sites associated with this compound. Based on the assignment of the emission features to specific sites, the symmetry of the first samarium environment is thought to be C3 or C3v while that associated with the second site appears to be C2v.

Reflectance Spectroscopy as a Monitor of the Thermal-Decomposition Products of Europium Trichloride Hexahydrate

ABSTRACT The thermal-decomposition products of EuCl3 · 6H2O can be monitored through the use of ultraviolet/visible reflectance spectroscopy. The use of reflectance spectroscopy proved complimentary to other spectroscopic methods, combining to give a more complete representation of the decomposition products. Using variations in spectral features of the reflectance spectra, the penta- and tetrahydrate decomposition products were identified, along with the tri- and di-monohydrate compounds that were identified by luminescence spectroscopy. The observed intermediates and their corresponding decomposition temperatures can be compared to those obtained by other methods. Structural and environmental inferences as indicated by the reflectance spectra are discussed.

A High Resolution Luminescence Study of two Novel Salts of the Triethvlenetetraaminehexaacetatoeuropate(III) Anion

Abstract A low-temperature high-resolution luminescence study of K3Eu(TTHA)·H2O and T13Eu(TTHA) ·H2O has been carried out. the Eu3+ luminescence spectrum was recorded over the spectral range which includes transitions from the 5D0 excited state to the 7F0-4 ground state manifolds. the observed spectral patterns are analyzed using group theoretical methods so as to deduce the site symmetry of the Eu3+ ion in the complex. the analysis shows that the Eu3+ ion occupies a spectroscopic site symmetry that approaches a D2 symmetry with distortion towards a C2 or lower symmetry in the potassium salt and a site symmetry of a C3 in the thallium salt. These salts illustrate the potential of the counterion to markedly influence the effective site symmetry of the Eu3+ ion.

Variation in the Luminescence Lifetimes of Eucl3·nH2O(N=0,L,2,3,6)

Abstract Eu3+ ion emission spectra and luminescence lifetimes were investigated for EuCl3 -nH2O (n=0,1,2,3,6). Each compound exhibited a characteristic set of emission bands and a specific luminescence lifetime. The number of water molecules and chloride ions coordinated to the Eu3+ ion in these materials was estimated from the observed lifetimes, spectroscopic implications, and expected lanthanide coordination numbers. Approximation of the observed luminescence decay constant for each material was possible through the use of arithmetic terms associated with both the complexed water molecules and the complexed chloride ions which make up the inner-coordination sphere of the Eu3+ ion.

A HIGH RESOLUTION LUMINESCENCE STUDY OF SILVER DIETHYLENETRIAMINEPENTAACETATOEUROPATE(III) MONOHYDRATE

Abstract A low-temperature high-resolution luminescence study of Ag2Eu(DTPA) H2O has been carried out. The Eu3+ luminescence spectrum was recorded over the spectral range which includes transitions from the 5D0 excited state to the 7F0-6 ground state manifolds and from the 5D1 excited state to the 7F0-2 ground state manifolds. The observed spectral patterns are analyzed using group theoretical methods so as to deduce the site symmetry of the Eu3+ ion in the complex. The analysis shows that the Eu3+ ion occupies a spectroscopic site symmetry that approaches a C2v symmetry with distortion towards C2 or lower symmetry. Results from the analysis are compared with previously reported Xray crystallographic results. In addition, the transition energies exhibited in the emission spectrum have been used to calculate the relative energies of the electronic levels characteristic of Eu3+ ions in the title compound.