Enhanced up-conversion luminescence from NaYF4:Yb,Er nanocrystals by Gd3+ ions induced phase transformation and plasmonic Au nanosphere arrays

Abstract

NaYF₄:Yb,Er nanocrystals with different concentrations of Gd³⁺ ions are prepared via a hydrothermal method. With increasing Gd³⁺ dopant, up-conversion (UC) emission is gradually enhanced and the strongest UC emission is improved by 50-fold for a sample with 15% Gd³⁺ doping compared with the one without Gd³⁺ incorporation. However, further increasing the Gd³⁺ dopant causes the reduction of UC emission which can be ascribed to the increased surface state recombination. Moreover, the self-assembly technique is used to fabricate Au nanosphere arrays with diameters of 300 nm to enhance the UC luminescence. It is found that the luminescence intensity is increased by 2-fold due to the surface plasmon resonance effect which is confirmed by the absorption spectra.