N.A. Stump

Study of the phase behavior of Eu2O3 under pressure via luminescence of Eu3

Abstract We have investigated the phase transition of Eu 2 O 3 under pressure from a C-type b.c.c. structure to a B-type monoclinic structure by the luminescence spectra of the Eu 3+ ion. It is suggested that the luminescence from f—f transitions in Eu 3+ is very sensitive to the Eu 3+ ion environment and can be used as a spectral probe to identify the crystal structure. The C-to-B transition occurs at about 8.0 GPa and the B-type structure was retained after the pressure had been released. The transition thermodynamics and kinetics are discussed, and the entropy for the C-to-B transformation was estimated. It was concluded that the C type is the room temperature and pressure stable structure, whereas the B type is metastable at room temperature.

Pressure-induced phase transition in YVO4:Eu3+: An emission lifetime study at high pressure

Abstract The dependence of the lifetime of the 5 D 0 level in the Eu 3+ ion doped into YVO 4 (denoted YVO 4 :Eu 3+ ) has been investigated as a function of pressure up to about 11 GPa, using a diamond anvil cell. An abrupt change in the lifetime of the Eu 3+ ion luminescence at 6.2 GPa, which after release of pressure did not change significantly, indicated that a pressure-induced, irreversible phase transition had occured. This result suggests that luminescence lifetime data can be used to identify phase transitions, and is particularly important when the luminescence spectra cannot differentiate between the site symmetries of the Eu 3+ ion in the two crystal structures involved, such as the case for YVO 4 :Eu 3+ .

Compounds of cerium, titanium and oxygen

Abstract The solubility of Ce 2 Ti 2 O 7 in Ln 2 Ti 2 O 7 (LnGd, Er and Lu) was determined experimentally. It was found that the solubility increases as the ionic radius of the host lanthanide element decreases. The lattice parameters of Ce 2 O 3. 4TiO 2 have been measured. The solubility of TiO 2−m in Ce 2 O 3 .3TiO 2−m ( m ≈0.11) was determined and the resulting solutions were investigated; the results indicate that an additional 2.5 TiO 2− m can be dissolved without significantly changing the lattice parameters. Limits for the solubility of Ce 4+ in compounds such as Ce 2 O 3 . n TiO 2 in which n =2 or 4 were also estimated.

Pressure-induced phase transition in YVO4:Eu3+ : a luminescence study at high pressure

Abstract The pressure dependence of the emission from the Eu 3+ ion in YVO 4 :Eu 3+ has been investigated to 14 GPa, using a diamond anvil cell. Abrupt changes in the luminescence spectra of Eu 3+ ion at 7 GPa, which, after removal of pressure, did not reverse, indicated that a pressure-induced, irreversible phase transition had occurred. The luminescence spectra from the high pressure phase showed the characteristics of a distorted D 2d symmetry, which can be explained by considering only the first coordination sphere oxygens about the Eu 3+ ion in an S 4 symmetry site. The change in the energy separation between the 5 D 0 and 7 F 0 levels from the low pressure phase to the high pressure phase is discussed. A decrease of the effective charge on the oxygen atoms in the high pressure phase occurs and is correlated with a charge transfer mechanism that arises because of the phase transition.

A luminescence study of B-type Eu2O3 under pressure

Abstract Luminescence spectra from Eu3 + ion in B-type (monoclinic) 2O3 powder have been recorded at room temperature as a function of pressure using a diamond anvil cell. Changes in the spectral pattern of the Eu3 + ion emission at about 4 GPa indicated that a phase transition to the A-type (hexagonal) structure had taken place. Upon release of the applied pressure, the B-type structure was regained with hysteresis. The spectral shifts with pressure have been used to study the effect of pressure on the spin-orbit interaction of the 4f electrons in the Ed + ion. The relationship between the relative changes in the spin-orbit coupling constant, ζ4f, and the volume accompanying the phase transition is also discussed.

Synthesis and spectral study of several solid M3[Eu(2,6-pyridinedicarboxylate)3] salts (M=Li+,Na+,K+,Rb+,Cs+,NH4+, and pyridinium+)

Abstract Salts of the [Eu(2,6-pyridinedicarboxylate)3]3- complex anion and various monovalent inorganic and organic counterions (Li+, Na+, K+, Rb+, Cs+, NH4 +, and pyridinium+) have been synthesized and studied by emission spectroscopy. The Eu3+ ion emission spectra exhibited by these salts have been observed with high resolution (less than 1.0 cm−1) and at low temperature (77 K). The emission spectra of these compounds indicate that changing the attached counterion does not affect the site symmetry observed by the europium ion beyond slight distortions indicated by small shifts in the energies of the Eu3+ electronic levels.

A high-resolution spectral study of Li3Eu(2,6-pyridinedicarboxylato)3

Several electronic levels of Li3Eu(2,6-pyridinedicarboxylato)3 have been studied through the use of low-temperature high-resolution single- and two-photon excitation emission spectroscopy. The observed shifts in the emission spectrum are described. The spectrum obtained exhibits the emission transitions characteristic for a EuIII ion in a distorted D3h symmetry site.

Perturbations of the luminescence spectra of europium-edta salts caused by selected monovalent counterions

Abstract High resolution emission studies of europium-EDTA salts of the form M(I)Eu(EDTA), where M≡Li, Na, K, Rb, Cs, Ag and Tl, have been carried out. Each europium-EDTA salt produced a distinct luminescence spectrum recorded over the spectral range which included the transitions in the europium(III) ion from the 6 D 0 level to the 7 F 0–4 levels. Spectral changes included slight shifts in peak position and varying line splitting patterns. Evaluations of the splitting patterns suggest that the site symmetries of the europium(III) ion in all compounds are low. Tentative site symmetry assignments have been made to fit best the observed luminescence spectra.

Europium oxychloride absorption spectroscopy as an optical probe of temperature

Abstract The temperature dependence of the features which arise from the 7F0,1 → 5D3 absorption transitions in EuOCl as seen by diffuse-reflectance spectroscopy has been investigated. The transitions shift linearly to higher energy with increasing temperature. The ratio of the intensities of the transitions arising from the 7F0 state to those arising from the 7F1 state also appears to be a linear function of temperature.

Luminescence detection of cation exchange in Na3[Eu(2,6-pyridinedicar☐ylato)3]

The exchange of several other cations for the Na + ions in Na 3 [Eu(2,6-pyridinedicarboxylato) 3 ] was investigated using Eu 3+ ion luminescence spectroscopy. Monovalent, divalent, and trivalent metal ions, as well as the monovalent ammonium ion, replaced the Na + ion via mass action to form various salts with the Eu(2,6-pyridinedicarboxylato) 3 3- complex anion. The detection of the cation exchange was achieved because of the sensitivity of Eu 3+ ion luminescence to the near environment of the Eu 3+ ion