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.% to 2.3 μm for Er3+ content in the range of 1 ≤ x < 6 mol.%,). In addition, the phosphors presented oval-like and quasipherical shapes for Er3+ content ≤ 1 mol.%. When the Er3+ concentrations are > 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.
Upconversion ytterbium erbium green emission lanthanum strontium aluminum oxide
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C. R. Garcia thanks to PRODEP-SEP 2017 Cuerpos Académicos and FONCYT-COECYT 2016 Projects and Universidad Autónoma de Coahuila (UAdeC) for the partial support to this work. M. Guzman-Rocha thanks CONACYT for the Ph.D. scholarship. Authors also appreciate the technical work performed by R. Valdivia, C. Albor and Martín Olmos from Centro de Investigaciones en óptica León México.
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