Abstract
Abstract CaSc2O4 phosphors codoped with 0.2% Er3+ and various concentrations (0–15%) of Yb3+ are prepared by high temperature solid-state reaction. Two Er3+ luminescence centers are observed and they are assigned to substitution for Ca2+ site (Er3+(I)) and Sc3+ site (Er3+(II)), respectively. We find that the Er3+(I) centers are preferentially formed at low doping concentration and their number starts to decrease along with the increase of the Er3+(II) centers on increasing Yb3+ concentration. Meanwhile, intense upconversion luminescence (UCL) with color tuning from green to red is observed upon 980 nm excitation. The decomposition of the UCL spectra exhibits the main contribution from the Er3+(I) centers in the range of Yb3+ concentration of this work. This result is attributed to efficient emissions of the Er3+(I) centers for the long lifetimes of Er3+(I) both on the green and red emitting levels. Furthermore, we have observed the UCL intensity of CaSc2O4: 0.2% Er3+, 15% Yb3+ is 4 times as strong as that in Y2O3: 0.2 Er3+, 15% Yb3+.
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