Tunable green/yellow upconversion emission and enhancement of the NIR luminescence in BaLaAlO4:Er3+ phosphors by codoping with Yb3+ ions

Abstract

This work reports the structural, morphological and luminescent properties of BaLaAlO4 doped with Er3+ and Yb3+ ions (BAL:Er,Yb). These phosphors were synthesized by the combustion method. The Yb concentration was varied from 0 to 12 mol% while the Er3+ concentration was fixed to 3 mol%. According to the analysis by X-ray diffraction, all the samples doped with different content of Yb presented an orthorhombic phase. The scanning electron microscopy revealed that the undoped BAL is formed by microcubes. For Yb concentrations of 0.5 and 1 mol%, the amount of cubes diminished by ≈ 70% and other morphologies such as 3D rectangles, nanorods and coalesced microparticles appeared. If the BAL:Er,Yb phosphors are doped with Yb concentrations of 3–7 mol%, only coalesced microparticles with irregular morphology are visualized. Moreover, nanorods mixed with coalesced microparticles are again observed in the sample doped with 12 mol% of Yb. On the other hand, the BAL:Er,Yb phosphors presented green and red upconversion emission bands after excitation with NIR light at 980 nm. Additionally, the BAL:Er,Yb phosphors showed an intense NIR emission band at 800 nm, which resulted from excitation of Er3+ ions. The BAL phosphors doped with 7 and 12 mol% of Yb were excited with a low power NIR LED of 70 mW and produced luminance values of 1365 and 1813 cd/m2 for the green and yellow emissions, respectively. Such high luminance and the emission of NIR light suggest that the BAL phosphors are good candidates for applications in lighting, displays and bioimaging.