Enhanced quantum efficiency and controllable emissions of Eu through incorporation of Mn²⁺ in β-NaYF₄ nanocrystals

Monodispersed Eu, Mn co-doped β-NaYF₄ nano-crystals with various morphologies, including nanoplates, hexagonal nanoprisms and microrod, have been prepared via a facile hydrothermal route. The trisodium citrate (Cit³⁻) and pH values, rather than Mn²⁺, play an important role in fine-tuning the morphologies. A broad band emission from the 5d-4f transition of Eu²⁺ as well as line emissions from the 4f-4f transitions of Eu³⁺ are observed in Eu, Mn co-doped β-NaYF₄. The quantum efficiency of Eu³⁺ was improved from 16% to 72% by inhibiting the luminescence of Eu²⁺. In addition, controllable emissions from Eu³⁺/Eu²⁺ can be achieved through the incorporation of Mn²⁺ in β-NaYF₄. The correlation between the tunable emission and enhanced quantum efficiency with Eu³⁺/Eu²⁺ and Mn²⁺ in β-NaYF₄ has been established and discussed in detail.