Enhanced red upconversion luminescence by codoping Ce3+ in β-NaY(Gd0.4)F4:Yb3+/Ho3+ nanocrystals

Abstract

In this work, hexagonal phase NaY(Gd_0.4)F₄:Yb³⁺/Ho³⁺ nanocrystals were obtained by solvothermal method. The upconversion emission tuning from green to red in NaY(Gd_0.4)F₄:Yb³⁺/Ho³⁺ nanocrystals was successfully achieved by replacing Y³⁺ ions in the nanocrystal structure with Ce³⁺ ions under 980 nm excitation. The red upconversion emission intensity was enhanced with Ce³⁺ concentration increasing. The output colors for the samples can be clearly observed in a confocal microscopy setup. It was found that two efficient cross-relaxation processes between Ho³⁺ and Ce³⁺ ions had been employed to enhance red emission and suppress green emission. The possible upconversion mechanisms and conversion efficiency between Ho³⁺ and Ce³⁺ ions were investigated in detail. In addition, the influence of the matrix and surface properties on the upconversion emission of the samples was also discussed. The red upconversion emission of Yb³⁺, Ho³⁺ and Gd³⁺ codoped nanocrystals in this work will have great potential applications in biological imaging, magnetic resonance imaging agents, and display and anti-counterfeiting applications.