One-pot synthesis of hexagonal NaLuF4:Yb,Er microcrystals with enhanced upconversion emission and high production yield

In this work, monodisperse β-NaLuF 4 :Yb,Er microcrystals with intense upconversion emission were synthesized via a modified hydrothermal method . With the increase of reactant concentration, their production yield is increased obviously, and the upconversion emission intensity in β-NaLuF 4 :Yb,Er microcrystals is also enhanced significantly. The luminescence enhancement should be attributed to minimal internal OH − defects, validated by a combination of analytical X-ray diffraction (XRD), energy dispersive spectrum (EDS), and Eu 3+ structural probe measurements. We also reveal that high Na + :RE 3+ ratio in the β-NaLuF 4 :Yb,Er microcrystals prepared under Na + -rich reaction will arouse the increased repulsive energy of β-NaLuF 4 microcrystals between F − and OH − anions and then facilitate the substitution of large OH − ions by small F − ions under F − -rich reaction conditions. Minimal OH − concentrations can limit nonradiative relaxation and promote excitation energy harvesting for high upconversion efficiency. The presented results not only offer a facile method for the simultaneous production yield and luminescence intensity increase of β-NaREF 4 microcrystals, but also uncover a better insight into the upconversion emission alterations, which is favorable to broaden their practical applications.