Effect of the Er3+ Co-dopant on the Green Upconversion Emission of LaSr2AlO5:Yb3+ Phosphors

Abstract

This work presents the structural, morphological and optical properties of LaSr2AlO5:Yb3+,Er3+ phosphors (LSA:Yb,Er) synthesized by a combustion method. The Yb3+ concentration was kept constant at 2 mol.%, while the Er3+ concentration changed from 0.2 mol.% to 6 mol.%. X-ray diffraction measurements revealed that all the LSA:Yb,Er phosphors presented a pure tetragonal phase. Scanning electron microscopy images show that LSA:Yb,Er phosphors increased their size as the Er3+ concentration increases (from 1.95 μm for Er3+ concentrations 1 mol.%, the LSA:Yb,Er phosphors present a notorious increase of conglomeration, and the particles had irregular morphologies. According to luminescence measurements, the LSA:Yb,Er phosphors present a green luminescence centered at 549 nm (λexc = 968 nm). The strongest green emission was observed for an Er3+ concentration of 1 mol.%, above this concentration, the green emission intensity decreases due to an excess of OH and carbonate groups on the surface of LSA:Yb,Er phosphors, as confirmed by the FTIR spectra. Moreover, the CIE coordinates for the green emission were tuned with the Er3+ concentration. These results suggest that LSA host could be a good candidate to produce upconversion emission when doped with rare earths, which could be attractive for the development of lighting sources.