Efficient near-infrared to visible and ultraviolet upconversion in polycrystalline BiOCl:Er3+/Yb3+ synthesized at low temperature

Er3+/Yb3+ co-doped BiOCl poly-crystals were synthesized by the conventional solid state method at 500 °C, which exhibited good crystalline and low phonon energy. Under 980 nm excitation, the samples showed intense red upconversion (UC) luminescence (Er3+: 4F9/2→4I15/2) as well as other four UC emission bands, including ultraviolet (UV) emission at 380 nm, violet emission at 411 nm, green UC emissions at 525 and 545 nm and near-infrared (NIR) emission between 800 and 850 nm, corresponding to the transitions of 4G11/2, 2H9/2, 2H11/2, 4S3/2 and 4I9/2→4I15/2 of Er3+, respectively. Interestingly, including the violet and green UC emissions, the red one originated a nearly three-photon process in this system, and a possible UC mechanism was proposed for the enhanced red emission.