Tin-(IV) dopant-controlled synthesis of Yb3+/Er3+:NaGdF4 nanocrystals: Morphology transformation and intensified upconversion performance

Hexagonal Yb³⁺/Er³⁺:NaGdF₄ nanocrystals codoped with Sn⁴⁺ ions were produced via an adjustive solvothermal approach. Simultaneous morphology regulation and intensified upconversion (UC) luminescence of Yb³⁺/Er³⁺:NaGdF₄ nanocrystals were achieved through Sn⁴⁺ ions doping. Upon introducing Sn⁴⁺ ions into the NaGdF₄ host, a part of the nanocrystals were converted to nanocubes. By optimizing the Sn⁴⁺ ions doping content to 40 mol%, UC luminescence intensity of the green and red emissions were intensified by 21 and 31 times, respectively. Moreover, the possible mechanisms for morphology transformation and UC luminescence enhancement of Sn⁴⁺-doped Yb³⁺/Er³⁺:NaGdF₄ nanocrystals were discussed elaborately. Additionally, in contrast to the sample fabricated by co-precipitation method, the result indicated that the UC luminescence intensity with 40 mol% Sn⁴⁺ ions doping was about 2.5 times higher than the former one. This research could be helpful for designing high-performance UC materials and fulfilling their practical applications.