Bifunctional NaGdF4:Yb, Er, Fe nanocrystals with the enhanced upconversion fluorescence

• NaGdF4:Yb, Er, Fe nanocrystals were synthesized by a facile hydrothermal method.
• The luminescence intensity can be improved greatly by Fe3+ doping.
• Fe3+ can enter crystal sites interstitially and substitutionally.
• These nanocrystals exhibit paramagnetic properties.

NaGdF4:Yb, Er nanocrystals doped with Fe3+ were synthesized by a facile hydrothermal method. The upconversion emissions in a broad range from 200 to 700 nm were measured under 980 nm laser excitation. The luminescence intensity can be improved greatly by Fe3+ doping. In addition to the typical upconversion emission of Er3+ ions, the violet emission from Gd3+ is explained by the energy transfer from Er3+ to Gd3+. Powder X-ray diffraction patterns reveal that Fe3+ can enter crystal sites interstitially and substitutionally. The effects of Fe3+ doping on morphology, crystal growth and emission properties of particles are discussed in detailed. Furthermore, these nanocrystals exhibit paramagnetic properties and have the potential applications in bimodal bioimaging in virtue of their upconversion luminescent and paramagnetic properties.