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

Abstract

Upconversion by ${\mathrm{Yb}}^{3+}$ sensitization in ${\mathrm{Er}}^{3+}$-doped ${\mathrm{YVO}}_4$ crystals has been studied under excitation with a 976 nm laser diode. In addition to the previously observed upconverted 526 and 554 nm ${\mathrm{Er}}^{3+}$ emission bands, three weak upconverted ${\mathrm{Er}}^{3+}$ 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 ${}^4{I}_{11/2}$ state of ${\mathrm{Er}}^{3+}.$ In addition to these emission bands, downconverted ${\mathrm{Yb}}^{3+}$ and ${\mathrm{Er}}^{3+}$ emission bands are simultaneously observed at 1010 and 1470–1630 nm, respectively. It is observed that the infrared ${\mathrm{Er}}^{3+}$ emission intensity increases linearly with pump power, while the ${\mathrm{Yb}}^{3+}$ emission intensity saturates at higher pump powers.