Phase controllable synthesis of NaMgF₃:Yb³⁺, Er³⁺ nanocrystals with effective red upconversion luminescence

Synthesizing and controlling lanthanide ions doped upconversion luminescent nanocrystals with effective emission have been researched to satisfy the demand for different applications. In this work, the influence of reaction conditions on crystal composition and upconversion luminescence properties of NaMgF₃:Yb³⁺, Er³⁺ nanocrystals have been explored with XRD and upconversion emission spectra. The experimental results demonstrate that lanthanide ions concentration has great impact on the growth of samples, i.e., a low concentration leads to cube NaMgF₃ nanocrystals, while a high concentration facilitates impurity NaYbF₄ microtube. Adjusting reaction parameters is also crucial for controlling NaMgF₃ crystal structure by shortening reaction time and reducing reaction temperature. In addition, the well-dispersed NaMgF₃:Yb³⁺, Er³⁺ nanocrystals with different red-to-green ratios have been achieved successfully by changing the reaction parameters, resulting in the upconversion luminescence from orange to red, and the single-band red UC luminescence can be observed in NaMgF₃:0.5Yb³⁺, 0.5Er³⁺ nanocrystals. This study explains the formation mechanism of NaMgF₃:Yb³⁺, Er³⁺ nanocrystals and gains the effective red luminescence, which may be helpful to synthesize other similar upconversion nanocrystals in colour display, bioimaging and so on.