Abstract
Greater enhancement in upconversion (UC) luminescence was observed in the glass–ceramics (GCs) containing CaF2:Yb3+, Er3+ nanocrystals (NCs) compared with whose doped with LaF3:Yb3+, Er3+ NCs prepared by conventional melt-quenching technique followed by successive heat treatment. Our joint experimental and theoretical studies suggest the lager enhancement of UC emission in CaF2–GCs rather than of LaF3–GCs is associated with the difference in the microstructures, the crystal size, the local coordination environment around rare earth (RE) ions as well as the structural rigidity in the silicate region of the GCs. In addition, it was found that a more symmetric ligand field around RE ions in a smaller size crystal which distributed more homogeneously within the highest ordering silicate region favors stronger UC emission by facilitating the energy transfer process and minimizing the rate of non-radiative relaxation process. Our results may enrich our understanding about UC process in oxyfluoride GCs and provide a general picture for the photophysical processes that contribute to the UC in similar GCs systems.
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