LAUSR

The average and local structures of ∼22 nm β-Er:Yb:NaYF4 upconverting nanocrystals were probed using a dual-space approach combining Rietveld and pair distribution function analysis of X-ray total scattering. Comparison of the fits provided by the structural models derived from P62m, P6, and P63/m space groups demonstrates that the latter yields a crystallochemically meaningful description of the nanocrystals’ average and local structures. This result is in line with those previously reported for bulk β-Na3xRE2–xF6 (x ∼ 0.45; RE = Y, Er, Tm, Yb) using powder X-ray diffraction,1 and for β-NaREF4 (RE = Y, Lu) nanocrystals using solid-state NMR;2 however, it differs from those reported in studies of β-NaREF4 (RE = La, Gd, Er) single crystals, which favored the structural model derived from the P6 space group.3 The proposed structural model features sodium cations distributed in four translation-equivalent chains, each shifted relative to the others along the c axis. Interestingly, the structural model der...