Effect of Yb3+ concentration on the green-yellow upconversion emission of SrGe4O9:Er3+ phosphors


C.R García

This work presents the structural, morphological and luminescent, properties of SrGe4O9 (SGO):Er3+,Yb3+
phosphors. These phosphors were synthesized by simple combustion synthesis and subsequently annealed at
1100 °C. The XRD patterns revealed that all the SGO samples doped with Yb3+ concentrations from 2 to 10 at.%
presented a trigonal pure phase (the Er3+ concentration was fixed to 1 at.%). The morphology of the SGO
samples was analyzed by scanning electron microscopy and found that they are formed by microparticles with
irregular shapes and average sizes in the range of 0.2 μm–3 μm. The luminescence measurements of the
SGO:Er3+,Yb3+ samples showed the presence of two main emission bands at 551 nm (green) and at 662 nm (red)
under excitation at 980 nm, which are associated to Er3+ transitions. For Yb concentration of 2 and 3 at.% the
green band dominated, but the red band became more intense for Yb concentrations above 5 at.%. As result, the
CIE coordinate changed from the green to the yellow region. The increase for the Yb content from 2 to 10 at.%
also enhanced of the NIR emission of Er3+ ≈5 times and the maximum upconversion emission was observed for
8% of Yb concentration. Further, the surface of the SGO samples was analyzed by the FTIR technique in order to
find OH groups which are common luminescent quenching centers, but these groups were not detected on the
samples. Since the SGO samples presented tunable emission, absence of OH groups on their surface and stable
crystalline structure for high Yb dopant concentrations, they could be good candidates as phosphors for solid
state lighting or displays applications.

Artículo-CERG 7 2019