A comparative investigation on upconversion luminescence in glass–ceramics containing LaF3 and CaF2 nanocrystals

Greater enhancement in upconversion (UC) luminescence was observed in the glass–ceramics (GCs) containing CaF 2 :Yb 3+ , Er 3+ nanocrystals (NCs) compared with whose doped with LaF 3 :Yb 3+ , Er 3+ 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 CaF 2 –GCs rather than of LaF 3 –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.