Nicholas M. Khaidukov

Two-photon spectroscopy of europium(III) elpasolites

We present polarized two-photon excitation (TPE) spectra, including Zeeman data, for europium(III) in the elpasolites Cs2NaEuCl6 and Cs2NaYF6:Eu3+. Approximately 80 and 60 levels of unambiguous symmetry have been assigned respectively in each compound up to 32 000 cm-1 with the aid of a one-electron crystal field Hamiltonian. This represents the most complete and extensive data set so far reported for Eu(III) at a cubic site. Comparisons are made between comparable data sets for Eu(III) f6 and Tb(III) f8. Deviations from the predictions of the one-electron crystal field model are discussed in terms of the spin correlation crystal field.

Vibrational and electronic spectra of

Single crystals of doped with molar concentrations of between 0.1 and 20% have been synthesized by the hydrothermal method, and studied by absorption, excitation and luminescence spectroscopy at temperatures down to 4 K. The observed spectral features were consistently assigned with reference to those of the corresponding europium hexachloroelpasolite. No distortion from octahedral symmetry was evident for the site in the 0.1 mol%-doped crystal, but small splittings of magnetic dipole zero-phonon lines in the spectra of the 20%-doped crystals are observed below 20 K. The vibrational behaviour of has been interpreted, and the energy-level scheme of the ion was deduced from the observed and inferred zero-phonon-line positions in the optical spectra. A parametrized Hamiltonian was fitted to 21 crystal-field levels of in . The fourth- and sixth-degree crystal-field parameters were about 1.6 times larger than for . The temperature shifts of the crystal-field levels were found to be negative, in contrast to the mostly positive shifts previously reported for actinide systems in octahedral symmetry, and were largely determined by the changes in the Slater parameters rather than the crystal-field parameters. A preliminary study has been made of the decay kinetics of the levels. is quenched by a cross-relaxation mechanism, and also by a thermally activated mechanism. The lifetime of does not exhibit a noticeable temperature or concentration dependence.

Emission and Excitation Spectra of Ce3+ and Pr3+ Ions in Hexafluoroelpasolite Lattices

The emission and excitation spectra of Ce(3+) and Pr(3+) doped into the cubic host Cs(2)NaYF(6) have been recorded at room temperature and ∼10 K using synchrotron radiation. The two 5d(1) T(2g) states of Ce(3+) have been located from the excitation spectra, whereas the E(g) state is placed above the host band gap. Decay measurements of the 5d(1) → 4f(1) Ce(3+) emission, and spectra collected using selective excitation, indicate the occupation of more than one type of site by Ce(3+) in this host lattice. By contrast, the location of features in the 4f(1)5d(1) → 4f(2) emission of Pr(3+) is independent of the excitation wavelength. Assignments are presented for some of the 4f(1)5d(1) levels and for the Pr(3+)-F(-) charge transfer band. The 5d emission lifetimes for Ce(3+) and Pr(3+) in the Cs(2)NaYF(6) host are 42 and 29 ± 1 ns, respectively, and are not temperature-dependent.