Relationship between microstructure and the achieving of the single-band red upconversion fluorescence of Er3+/Yb3+ codoped crystallites

The as-cast and the heat-treated samples with the primary mole composition of (59.4 − x)ZnF2–40PbF2–0.1B2O3–xYb2O3–0.5Er2O3 (x = 2, 4, 7, 10, 13) were synthesized. In the as-cast and the heat-treated samples with 13 mol% Yb2O3, the multi-band and the single red band upconversion (UC) lights were observed, respectively, under the excitation of a laser diode (LD) with excitation wavelength of 980 nm. For this interesting phenomenon, microstructure analysis revealed that the crystal phases and the distribution of Er3+ ion has been changed by the heat-treatment and the mole ratio of Yb3+ to Er3+ ion in the neighbor environment of Er3+ ion is increased from 0.74 to 16.96 which brought about the populating behavior variation of 4F7/2 and 4F9/2 levels of Er3+ ions, to which the achieving of the dazzlingly single-narrow-band red light was ascribed.