Simultaneously optimizing fluorescent and paramagnetic properties of bifunctional NaGdF4:Yb3+/Er3+ nanocrystals by crystal field tuning

Here, we show the simultaneous enhancement of fluorescent and paramagnetic properties in bifunctional NaGdF4:Yb3+/Er3+ nanocrystals by crystal field tuning. The energy level splitting calculation indicates, that lanthanide ionic pairs La3+/Lu3+ introduced into the NaGdF4 host can modify the crystal field around emitters (e.g., Er3+ and Tm3+) and sensitizers (e.g., Yb3+) that result in the broadening of crystal field splitting of energy levels and the abundant multi-site distribution of upconversion luminescence. The optimization of the paramagnetic properties in NaGdF4 doped with emitters and sensitizers is ascribed to the lowering of anti-ferromagnetic coupling.