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

Graphical abstract: Crystal field tuning is a powerful approach for simultaneously enhancing the optical and magnetic properties of lanthanide-doped NaGdF₄ bi-functional nanocrystals. - Abstract: 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