Potassium ytterbium fluorides with predictable crystal phases and architectures, such as KYb 3 F 10 nanoparticles, KYb 2 F 7 sub-microplates, microrods, KYbF 4 microplates, micro-bipyramids, K 2 YbF 5 microprims and microrods have been successfully synthesized by simply 10 tuning the molar ratio of KF to Yb 3+ via a facile and general solution-based route. The influence of the KF dosage on phase and morphology evolution of potassium ytterbium fluorides has been systematically investigated and discussed. And the mechanism about how KF/Yb 3+ molar ratio influences the anisotropic growth and phase, morphology evolution was proposed. Taking K 2 YbF 5 mcirorods as an example, the possible formation mechanism was presented on the basis of XRD patterns and the corresponding SEM images of the intermediate products obtained at different reaction time intervals. Additionally, the upconversion luminescence properties of Er 3+ ions (2 15 mol%) doped potassium ytterbium fluorides with different crystalline phases and architectures were studied in detail. Importantly, this study may provide a great opportunity for systematical study of the general synthesis and luminescence properties of potassium ytterbium fluorides with predictable crystal phases and well-defined morphologies, which can offer a reference for the precisely controlled synthesis of other rare earth fluoride compounds.