Bright and tunable up-conversion luminescence through cooperative energy transfer in Yb3+, Tb3+ and Eu3+ co-doped LaPO4 nanocrystals

Abstract

Lanthanum phosphate LaPO₄ nanocrystals doped with Yb³⁺, Tb³⁺ and Eu³⁺ ions, were synthesised by a hydrothermal method followed by annealing at 900 °C. These materials exhibited bright and tunable up-conversion luminescence from green to red colour as the result of Tb³⁺ and Eu³⁺ ions emission. The structural and morphological properties of the products were analysed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The spectroscopic properties of LaPO₄:Yb³⁺,Tb³⁺,Eu³⁺ nanocrystals were investigated using excitation and emission spectra. Also the luminescence decays were measured showing an unusually long rise time of the luminescence as a result of cooperative energy transfer mechanisms (CET) followed by energy migration. Calculated energy transfer rates and efficiencies showed the effectiveness of energy transfer between Yb³⁺, Tb³⁺ and Eu³⁺ ions.