Upconversion emission in Er3+/Yb3+-codoped YVO4 crystals

Upconversion by Yb3+ sensitization in Er3+-doped YVO4 crystals has been studied under excitation with a 976 nm laser diode. In addition to the previously observed upconverted 526 and 554 nm Er3+ emission bands, three weak upconverted Er3+ emission bands are observed at 490, 660, and 670 nm at room temperature. From the quadratic pump-power dependence, it is confirmed that the upconversion is induced by a two-photon excitation process involving excited-state absorption from the I-4(11/2) state of Er3+. In addition to these emission bands, downconverted Yb3+ and Er3+ emission bands are simultaneously observed at 1010 and 1470-1630 am. respectively. It is observed that the infrared Er3+ emission intensity increases linearly with pump power, while the Yb3+ emission intensity saturates gt higher pump powers.