Doping induced morphology, crystal structure, and upconversion luminescence evolution: from Na3ScF6:Yb/Er/Y to NaYF4:Yb/Er/Sc nanocrystals

Impurity doping not only provides a fundamental approach to impart unique electronic, magnetic and optical properties to target nanomaterials, but also has critical influence on nucleation and growth of many functional nanocrystals. In the current study, Y3+ and Sc3+ were adopted to tune the shape, size, and upconversion luminescence properties of Na3ScF6:Yb/Er and NaYF4:Yb/Er samples, respectively. When Y3+ doping concentration was lower than 10 mol%, the size and shape of Na3ScF6:Yb/Er (18/2) nanoparticles gradually changed from similar to 18 nm rhombus to 36 nm spheres. Subsequently, the co-existence of Na3ScF6:Yb/Er and NaYF4:Yb/Er nanoparticles was observed during 20 mol%-50 mol% Y3+ doping, and finally NaYF4:Yb/Er nanoparticles became the only product at > 60 mol% Y3+ doping where the role of Sc3+ turned into dopant and the size of nanocrystals decreased from similar to 30 to 20 nm gradually. Both Y3+ and Sc3+ ions doping could enhance the upconversion luminescence intensity of Na3ScF6:Yb/Er and NaYF4:Yb/Er samples, for which possible mechanism was proposed from the perspective of crystal structure. Finally, the upconversion luminescence details were disclosed.