The energy transfer mechanism in Pr3+ and Yb3+ codoped β-NaLuF4 nanocrystals

Abstract

The Pr³⁺ and Yb³⁺ codoped β-NaLuF₄ hexagonal nanoplates with a size of 250 nm × 110 nm were synthesized by a solvothermal process. X-Ray diffraction and scanning electron microscopy were used to characterize the crystal structure and morphology of the materials. The visible and near infrared spectra as well as the decay curves of Pr³⁺:³P₀ level were used to demonstrate the energy transfer from Pr³⁺ ions to Yb³⁺ ions. The downconversion phenomenon has been observed under the direct excitation of the ³P₂ level of Pr³⁺. According to the analysis of the dependence of the initial transfer rate upon Yb³⁺ ion concentration, it indicates that the ET from Pr³⁺ ions to Yb³⁺ ions is only by a two-step ET process when the Yb³⁺ concentration is very low; however, with the increase of the Yb³⁺ concentration, a cooperative ET process occurs and gradually increases; when the Yb³⁺ ion concentration increases to 20 mol%, the ET from Pr³⁺ ions to Yb³⁺ ions occurs only by the cooperative ET process. When the doping concentration of Yb³⁺ ions reaches 20 mol% at a fixed concentration of Pr³⁺ ions (1 mol%), the theoretical quantum efficiency is 192.2%, close to the limit of 200%. The current research has great potential in improving the conversion efficiency of silicon solar cells.