We have performed a detailed study of the magnetic and electronic properties of highly manganese-doped β-NaGdF4 and β-NaEuF4 nanoparticles with a narrow size distribution. XPS as well as XRF experiments confirm the successful doping of 11 ± 2% Mn into β-NaGdF4 and β-NaEuF4 nanoparticles, i.e., a much higher Mn concentration than has been previously reported for the incorporation of bivalent transition metal ions into the β phase of NaREF4 (RE = rare earth) nanocrystals. Owing to the high manganese concentration, we observed quenching of the Mn2+ emission in both materials and even quenching of the red Eu3+ emission in β-NaEuF4:11% Mn particles. We have investigated the Mn–Mn magnetic interactions by means of EPR spectroscopy, and SQUID magnetometry further supports a significant increase of the magnetization of the Mn-doped β-NaEuF4 nanoparticles compared to pure β-NaEuF4. By using element specific X-ray absorption spectroscopy and X-ray magnetic circular dichroism, we show that the magnetism of Mn-doped β-NaEuF4 is dominated by the divalent Mn ions for Mn-doped β-NaEuF4. A parallel alignment of the gadolinium and manganese magnetic moments is found.

is an interesting shell material for β-NaREF4 particles of the lighter lanthanides (RE = Ce, Pr, Nd), as variation of its strontium content x allows to vary its lattice parameters and match those of the core material.