Controllable hydrothermal synthesis of NaYbF4 and YbF3 with diverse morphologies and emission enhancement in β-NaYbF4: Er3+ upconversion micro-crystals via solvents codoping and Na+ dosage

As a matrix material, NaYbF4 has attracted more and more attention due to its large absorption cross section and high energy transfer efficiency. In this study, lanthanide doped NaYbF4 upconversion (UC) nano-/micro-crystalline was carefully synthesized by hydrothermal method. The influence of kinds of external conditions, including reaction time, initial reaction solution pH value, organic solvents codoping, and Na+ concentration on crystalline phase, size, morphology and especially luminescent property are systematically studied and the possible formation mechanism based on PH values is emphatically proposed. The products of NaYbF4 with various morphologies range from nanospheres, microprisms, microdisks, hexagonal crown-capped shapes, hexagonal clam-like shapes and hexagonal flower-like shapes were successfully prepared. The results show that the up-conversion luminescence property is positively correlated with the slenderness ratio. Solvents codoping and Na+ concentration can greatly improve the luminescence property, especially for red emission. Impressively, the emission colors and intensities might be finely tuned through finely tuning the PH values, solvents co-doping and Na+ dosage. Furthermore, this study will be expected to contribute to the synthesis of various morphologies and improving the UC intensity of lanthanide doped crystals.