Cooperative and White Light Emission from Yb- and Yb,Er-Doped Y2Si2O7 Nanopowders

We have investigated the luminescence properties of of Y₂Si₂O₇ nanopowders doped with (1) Yb only and (2) Yb and Er.  Under 980 nm excitation of the Yb-only sample, the system exhibits a blue emission, which we attribute to cooperative emission from Yb pairs. When the air pressure in the sample holder is reduced to very low pressures, a broad band “white” emission, extending from the blue into the near IR, appears, and the blue Yb emission band disappears. In the Yb-Er doped system, no cooperative emission from Yb is observed, but the Er emission bands are observed throughout the visible region. These Er emissions result from upconversion processes through energy transfer or through a combination of energy transfer and excited state absorption. The broad band white light emission is also observed in this sample, and becomes the more favorable emission as the pressure is decreased and the pumping intensity increased.