Molten-salt synthesis and upconversion of hexagonal NaYF4:Er3+:Yb3+ micro-/nano-crystals

The NH4NO3 molten solution system was developed to synthesize Er3+/Yb3+-doped hexagonal NaYF4 micro-/nano-crystals with different sizes and morphologies. The influences of the reaction temperature, the reaction time, the usage amounts of reaction materials and flux NH4NO3 on the structure and morphology were studied and discussed in detail. The effect of the sizes and morphologies on the upconversion properties was also investigated detailedly. The rod-like particles exhibit much stronger UC emission than for those with other shapes. The abnormal characteristics of the strong UC emission for the phosphors with the length of 80-100 nm and the diameter of ca. 50 nm was also observed. This work demonstrates a rational approach to synthesis high-quality fluorides and other types of materials in NH4NO3 molten solution system, as well as a possibility to meet the increasing commercial demand.