Controllable synthesis and upconversion emission of ultrasmall lanthanide-doped Sr2GdF7 nanocrystals

• Sr2GdF7 NCs were synthesized via solvothermal method using oleic acid as capping ligands.
• Apropos Gd3+ ions content (0.30–0.45 mmol) is favorable to the formation of pure phase Sr2GdF7 NCs.
• The average crystalline size of the products can be controlled less than 10 nm.
• By lanthanide ions doping intense green, yellow, and white-color UC emission were obtained under the excitation of a 980 nm laser.
• The doping concentration of lanthanide ions was optimized, which makes the NCs show maximum intensities.

The effect of rare-earth ions content on the phase structure, crystal size and morphology of SrF2–GdF3 system were studied under solvothermal conditions. By tuning the molar ratio of reactants, tetragonal phase Sr2GdF7 nanocrystals (NCs) were synthesized via solvothermal method using oleic acid as capping ligands. The effects of reaction conditions on the phase structure, crystal size, morphology, and upconversion (UC) emission properties of the products were investigated. The results reveal that apropos Gd3+ ions content (0.30–0.45 mmol) is favorable to the formation of pure phase Sr2GdF7 NCs with more uniform size distribution. The average crystalline size of the products can be controlled less than 10 nm. The energy transfer UC mechanisms for the fluorescent intensity were also investigated. Following Yb3+, Er3+, Tm3+ and Ho3+ ions doping, the Sr2GdF7 NCs show intense green, yellow, and white-color UC emission under the excitation of a 980 nm laser, and the doping concentration of lanthanide ions was optimized, which makes the NCs show maximum intensities under the excitation of a 980 nm laser.