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In this work, beta-NaYF4:Yb3+/Tm3+ samples with controllable
morphologies have been prepared using a facile hydrothermal method. The
overall morphologies of the samples can be adjusted from rod-shape to
hexagonal prism-shape with crown-like top end, and then to hexagonal
plate-shape by increasing the pH values of initial solutions ranging
from 3 to 9. Furthermore, the pH values of the initial solutions show
great effect on upconversion emissions of the samples, and it is worth
noting that higher both near-infrared emission and chromatic purity are
observed for the samples obtained under lower pH values conditions. The
corresponding mechanism may be attributed to the combination of more
Yb3+ ions incorporated in the lattice and the reduced lattice constants
under the condition of lower pH values, favoring energy transfer between
Yb3+ and Tm3+ ions or between two neighboring Tm3+ ions. (C) 2013
Elsevier Ltd. All rights reserved.
