Synthesis of NaYF$_4$:Yb, Er up-conversion luminophore from nitrate flux

The behavior of nanoparticle ensembles was studied using of NaRF4 hexagonal phases. The evolution of particles in the process of rapid and productive synthesis from flux as a result of a chemical reaction was investigated. A low-temperature synthesis process in the medium of sodium nitrate was used. Synthesis of the samples of up-conversion phosphor NaY$_{0.78}$Yb$_{0.2}$Er$_{0.02}$F$_{4}$ was performed from rare-earth nitrates at 350–430$^{\circ}$C for 15–500 min. NaF was used as the fluorinating agent. Powder X-ray phase analysis and scanning electron microscopy revealed a rapid transformation of the cubic alpha modification into a hexagonal phase, followed by the transformation of nanoparticles into hexagonal prisms of micron sizes. The up-conversion luminescence energy yield increased as the reaction time increased.