Photoluminescence and optical absorption of Cs2NaScF6 : Cr3+

The main objective of this paper is the characterization of the spectroscopic properties of new materials that are prospective laser media. This approach allows for the comparison of the properties of the Cr3+ in different environments. Here, we have studied the photoluminescence and optical absorption of Cs2NaScF6:Cr3+ single crystals. On the basis of near-infrared luminescence measurements at 2, 77, and 300 K the observed lines originated from the Cr3+-centres were associated with the T-4(2)(F-4) --> 4A(2)(F-4) transition and the lifetimes were obtained. In spite of the quenching observed as a function of temperature at least 10% of the 2 K emission intensity for Cs2NaScF6 doped with 1% of Cr3+ remains at room temperature. Besides, the 2 K emission broad band could be well described in terms of normal modes of the octahedral complex [CrF6](3-), and the Racah and crystal-field parameters calculated.16331732

Inelastic neutron scattering studies of TbNiAlH<inf>1.4</inf> and UNiAlH<inf>2.0</inf> hydrides

The optical vibrations of hydrogen in TbNiAlH1.4 and UNiAlH2.0 were investigated by means of inelastic neutron scattering. The experimental data were analysed, including multiphonon neutron scattering contributions, calculated in an isotropic harmonic approximation. At least two fundamental H optical peaks were observed in TbNiAlH1.4, and were assigned to the vibrational modes of hydrogen atoms occupying different interstitial sites in the metal sublattice. The high-energy part of the UNiAlH2.0 spectra is characterized by strong anharmonicity, and a broad fundamental band. The latter can be accounted for by a large dispersion of phonon modes due to the strong H-H interactions, and/or different metal-hydrogen force constants, which may originate from different metal atoms surrounding the H atoms in the unit cell