Mechanism and efficiency of quantum cutting luminescence in Pr3+/Yb3+ co-doped NaLu(WO4)2 phosphors

This work aims to explore the quantum cutting mechanisms and efficiency of Pr 3+ /Yb 3+ co-doped NaLu(WO 4 ) 2 phosphors synthesized via a high-temperature solid state reaction. To optimize Pr 3+ doping concentration, the spectral properties of Pr 3+ single-doped NaLu(WO 4 ) 2 phosphors were examined. The optimum Pr 3+ concentration was found to be 5 mol%, at which the emission intensity from the 3 P 0 level reaches a maximum. Moreover, spectroscopic and dynamic analyses further indicated that the concentration quenching of 3 P 0 and 1 G 4 levels occurs via electric dipole-dipole interaction between Pr 3+ ions. The luminescence mechanisms in NaLu(WO 4 ) 2 : 5 mol% Pr 3+ , x mol% Yb 3+ phosphors were elucidated through the dependence of the steady spectroscopic properties on the Yb 3+ concentration. It was found that the infrared emission of Yb 3+ originates via two distinct pathways: one involves two-step energy transfers from Pr 3+ in 3 P 0 and 1 G 4 to Yb 3+ , namely 3 P 0 + 2 F 7/2  →  1 G 4 + 2 F 5/2 and 1 G 4 + 2 F 7/2  →  3 H 4 + 2 F 5/2 , and the other arises from direct sensitization of Yb 3+ by Pr 3+ in 1 D 2 via one-step energy transfer 1 D 2 + 2 F 7/2  →  3 F 4 + 2 F 5/2 . In addition, the Pr 3+ itself could produce an infrared emission from 1 G 4 to 3 H 4 . Based on the confirmed luminescence mechanisms, the luminescence efficiencies of the Pr 3+ /Yb 3+ co-doped NaLu(WO 4 ) 2 phosphors were calculated by taking the corresponding energy transfer efficiencies, radiative transition efficiencies, and non-radiative transition efficiencies, and the factors influencing the total luminescence efficiency were analyzed.