Controlled Synthesis of BaYF5:Er3+, Yb3+ with Different Morphology for the Enhancement of Upconversion Luminescence

In this work, Er3+/Yb3+-codoped BaYF5 with different sizes and shapes have been synthesized by a simple solvothermal method. By changing the fluoride source, pH value, solvent, surfactants, Yb3+ concentration, temperature, and reaction time, the optimum synthetic conditions of BaYF5:Er3+, Yb3+ were found to improve the upconversion luminescent properties. It is found that the emission intensity of green and red light is enhanced for several times by the way of using NaBF4 as a fluoride source with the comparison of NH4F and NaF. Moreover, the effects of different surfactants are not the same. Adding 5% polyetherimide (PEI) as surfactant can also improve the upconversion emission. On the contrary, when sodium citrate (CIT) as another surfactant was used to add, the sizes of the nanocrystals were gradually increased and the luminous properties also declined.