Structural and Spectroscopic Characterization of Active Sites in a Family of Light‐Emitting Sodium Lanthanide Tetrafluorides

Abstract

Illuminating disorder: Many highly efficient light emitters are members of the family β‐NaLnF4 (Ln=Y, La–Lu). Diffuse X‐ray scattering is combined with single‐crystal absorption spectroscopy at cryogenic temperatures to unambiguously identify and characterize two crystallographically inequivalent spectroscopic sites (A and B). The high light yield is correlated with the existence and nature of these sites.

Energy transfer between UO22+ and Eu3+ in β-NaYF4

“…Emission from 5 D J (J = 0, 1, 2) is observed with the transitions from J = 2 being more prominent at the lower temperature due to slower nonradiative relaxation processes. There is now a general consensus that the crystal structure of ␤-NaYF 4 with Z = 1.5 (or more clearly, Na 1.5 Y 1.5 V Na F 6 ) belongs to the space group P6 [14][15][16]. The Y 3+ ions occupy the Wyckoff site 1a with C 3h site symmetry and also share the site 2h (point group symmetry C 3 ) with Na + cations.…”

Infrared luminescence of transparent glass ceramic containing Er3+:NaYF4 nanocrystals

“…On further increasing the temperature to the third stage, a phase transition of NaYF 4 from cubic to hexagonal takes place, as reported in our previous work [7]. The cubic NaYF 4 has a fluorite lattice with a random distribution of Y 3+ ions [9]; however, the hexagonal NaYF 4 is a more ordered phase: Y 3+ ions occupy regularly the nine-fold coordinated sites, thus there are only two different spectroscopic sites [10]. The Er 3+ ions dissolved in the NaYF 4 nanocrystals are believed to substitute the Y 3+ ions for their same charge and similar ion radius; therefore, the phase transition leads to the limitation of Er 3+ spectroscopic sites, which certainly narrows the emission band.…”

Analyzing diffuse scattering with supercomputers

“…Here we focus on static disorder associated with local structural variations. Qualitative DS analysis can show general aspects of disorder, but only a quantitative analysis can reveal details of the deviations from the average (or Bragg) structure and provide a basis for explaining the origin of the functional properties (Welberry & Goossens, 2008;Aebischer et al, 2006). Only the disordered atoms or molecules within the overall structure contribute to diffuse scattering, which, being distributed over extensive volumes of reciprocal space, is usually orders of magnitude weaker per unit volume of scattering space than Bragg diffraction.…”