High upconversion quantum yield at low pump threshold in Er3+/Yb3+ doped La2O2S phosphor

In this letter, we report the absolute upconversion quantum yields (QY) for 9% Yb3+ and 1% Er3+ co-doped La2O2S and its comparison with NaYF4 doped with 20% Yb3+, 2% Er3+ for all the upconversion emissions centered at 410, 550, 667, and 822 nm at various excitation power densities at 977 nm excitation. The maximum upconversion QY for 9% Yb3+ and 1% Er3+ co-doped La2O2S was measured to be 5.83 +/- 0.87% at the excitation power density of 13 W/cm(2). An excitation power dependent study revealed that although absolute upconversion QY measured for NaYF4: 20% Yb, 2% Er is higher at higher excitation power densities, La2O2S: 9% Yb, 1% Er possesses higher QYs at the lower excitation power densities. (c) 2013 Elsevier B.V. All rights reserved.