VIBRATIONAL AND ELECTRONIC-SPECTRA OF EUF6(3-)

Single crystals of Cs2NaYF6 doped with molar concentrations of Eu3+ be tween 0.1 and 20% have been synthesized by the hydrothermal method, an d studied by absorption, excitation and luminescence spectroscopy at t emperatures down to 4 K. The observed spectral features were consisten tly assigned with reference to those of the corresponding europium hex achloroelpasolite. No distortion from octahedral symmetry was evident for the Eu3+ site in the 0.1 mol%-doped Cs2NaYF6 crystal, but small sp littings of magnetic dipole zero-phonon lines in the spectra of the 20 %-doped crystals are observed below 20 K. The vibrational behaviour of EuF63- has been interpreted, and the energy-level scheme of the Eu3ion was deduced from the observed and inferred zero-phonon-line positi ons in the optical spectra. A parametrized Hamiltonian was fitted to 2 1 crystal-field levels of Eu3+ in Cs2NaYF6. The fourth-and sixth-degre e crystal-field parameters were about 1.6 times larger than for Cs2NaE uCl6. The temperature shifts of the crystal-field levels were found to be negative, in contrast to the mostly positive shifts previously rep orted for actinide systems in octahedral symmetry, and were largely de termined by the changes in the Slater parameters rather than the cryst al-field parameters. A preliminary study has been made of the decay ki netics of the D-5(J) (J = 0, 1,2) levels. D-5(2) is quenched by a cros s-relaxation mechanism, and SDI also by a thermally activated mechanis m. The lifetime of D-5(0) does not exhibit a noticeable temperature or concentration dependence.