Ultrasmall Lanthanide-doped NaMgF3 Nanocrystals: Controlled Synthesis and Optical Properties

Orthorhombic-phase NaMgF3, composed of bio-friendly elements of Na, Mg and F, is considered to be an ideal host matrix for preparing trivalent lanthanide (Ln(3+))-doped luminescent nanocrystals (NCs) with color-tunable emissions for diverse biological applications. However, the preparation and the survey on optical properties of ultrasmall (< 10 nm) Ln(3+)-doped NaMgF3 NCs remain nearly untouched to date. In this paper, we report a series of monodisperse Ln(3+) -doped orthorhombic-phase NaMgF3 NCs with an average size of similar to 10 nm that was synthesised by using a modified high-temperature co-precipitation method. Utilizing Eu3+ ion as an efficient optical/structural probe, the successful hetero-valence doping of Ln(3+) ion into the lattice of NaMgF3 NCs is well-established irrespective of their different valences and radii between the host cation (e.g. Mg2+) and Ln(3+) dopant. Benefiting from this, desirable upconversion luminescence (UCL) ranging from ultraviolet (UV) to visible and to near-infrared (NIR) spectral regions can be easily obtained after the doping of typical UCL couples of Yb3+/Er3+, Yb3+/Tm3+ and Yb3+/Ho3+ into the NaMgF3 NCs upon excitation by using a 980-nm diode laser.