Ultraviolet to near-infrared downconversion in Yb3+-doped Sr2CeO4

Efficient bluegreen emission is observed for Sr2CeO4 under ultraviolet excitation ranging from 250 to 400?nm and this is ascribed to the emission of the O2-Ce4+ charge transfer (CT) states. Under the excitation of ultraviolet light in the broad absorption band, an intense near-infrared (NIR) emission of Yb3+: 2F5/2???2F7/2 around 1 mu m is observed for Yb3+-doped Sr2CeO4. The Yb3+ concentration-dependent luminescence properties and the lifetimes of both the visible CT emission and the NIR Yb3+ emission are investigated under the excitation of a 266-nm pulsed laser beam. The fast decline of the lifetimes of the CT emission with the increasing Yb3+ concentration suggests efficient energy transfer from the host to Yb3+ ions. A cooperative energy transfer (CET) mechanism is proposed to explain the NIR downconversion process. The Sr2CeO4:Yb3+ phosphors can convert ultraviolet photons into NIR photons around 1 mu m with a twofold increase in the photon number via CET, which has potential application in enhancing the photovoltaic conversion efficiency of silicon-based solar cells.