808Â nm NIR light excited single-band red upconversion emission in lanthanide-doped KMnF3 nanocrystals

•A strategy to achieve 808 nm excited single-band red UC emission has been provided.•Nd3+/Yb3+/Er3+ tri-doped KMnF3 nanocrystals are synthesized by solvothermal method.•The corresponding energy transfer mechanism have been discussed in detail.•A new type of UCNPs is developed as attractive alternative for deep-tissue imaging.

A new type of upconversion nanoparticles (UCNPs) whose excitation and emission peaks are both located in the biological window has been developed based on the combination of Nd3+ sensitization and efficient energy transfer between Mn2+ and Er3+ ions. In our design, Nd3+ ions act as sensitizers for efficient absorption of 808 nm NIR photons, while the usage of Yb3+ ions as energy migrators facilitates the efficient energy transfer from Nd3+ to Er3+ ions. More importantly, the introduction of Mn2+ ions plays a key role in the realization of single-band red UC emission of Er3+ ions via the efficient energy transfer process between Mn2+ and Er3+. Consequently, upon 808 nm laser excitation, single-band red UC emission can be obtained in the as-synthesized Nd3+/Yb3+/Er3+ tri-doped KMnF3 nanocrystals, which could be considered as attractive alternative to conventionally used UCNPs for deep-tissue imaging with mitigation of the attenuation effect associated with the emission peaks outside biological window and the overheating constraints imposed by the conventional 980 nm laser excitation.