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)-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-doped NaMgF3 NCs remain nearly untouched to date. In this paper, we report a series of monodisperse Ln-doped orthorhombic-phase NaMgF3 NCs with an average size of ～10 nm that was synthesised by using a modified high-temperature co-precipitation method. Utilizing Euion as an efficient optical/structural probe, the successful hetero-valence doping of Lnion into the lattice of NaMgF3 NCs is well-established irrespective of their different valences and radii between the host cation(e.g. Mg2+) and Lndopant. 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 Yb/Er, Yb/Tmand Yb/Hointo the NaMgF3 NCs upon excitation by using a 980-nm diode laser.