Preparation, upconversion luminescence, and solid-state NMR studies of water-soluble hexagonal NaScF4:Yb/Er microcrystals

Water-soluble hexagonal NaScF4:Yb/Er upconversion microcrystals (UCMCs) were synthesized using the hydrothermal method. The upconversion photoluminescence properties of NaScF4:xYb/2%Er microcrystals (x = 4-20%) were characterized under a 980-nm-wavelength laser excitation. The dependence of red/green (R/G) ratio on the concentration of Yb3+ ions was investigated. The local environments of dopant ions (Yb3+, Er3+) in NaScF4 were studied using multiple solid-state nuclear magnetic resonance (NMR) techniques. The 19F single pulse and 19F{23Na} and 19F{45Sc} rotational echo double resonance (REDOR) techniques proved that the dopant rare-earth ions (Yb3+, Er3+) preferred to substitute Na+ rather than Sc3+ ions. Such solid-state NMR techniques provide a novel approach to study new phosphors.