Enhanced upconversion luminescence and single-band red emission of NaErF4 nanocrystals via Mn2+ doping

In this paper, the monodispersed NaErF4:Yb, Mn nanoparticles (NPs) were successfully synthesized by a simple and mild solvothermal method. The as-prepared NPs were characterized by X-ray diffraction, transmission electron microscopy, and spectrophotometer. The crystal phase, size, morphology, and upconversion (UC) properties of these NPs can be readily tuned by doping Mn2+. With increasing Mn2+ contents, the crystal phase of NaErF4:Yb NPs was transferred from hexagonal to cubic, and then a new orthorhombic phase NaMn3F10 appeared. The morphology of NaErF4:Yb was tuned from nanodisks to nanocubes and then to large nanoflakes with increasing Mn2+ dopant contents. Moreover, the UC luminescence (UCL) intensity can be enhanced by increasing Mn2+ content. Interestingly, single-band red emission can be achieved when the Mn2+ content reaches 20%. This is mainly ascribed to the efficient energy transfer between Er3+ and Mn2+. The enhanced UCL intensity and single-band red UCL make these NaErF4:Yb/Mn NPs ideal probes for optical bioimaging owing to the low tissue absorption and deep tissue penetration of red light.