The influence of Yb3+ ions on the structural and near infra-red (NIR) emission of the SrF2:Eu2+/Pr3+ down-conversion containing Na+ ions were investigated for solar cell applications. Most of the down-conversion studied materials for solar cell application are based on energy transfer from lanthanide ions to Yb3+ ions. For fluoride materials the charge compensation mechanism is of fundamental importance to maintain the electrical neutrality of the crystals. The x-ray diffraction data indicated that a mixture of cubic SrF2 and NaYbF4 phases gradually formed with increasing Yb3+ doping concentration. X-ray photoelectron spectroscopy (XPS) also confirmed the formation of the mixed fluoride structures. The F 1s peak showed two peaks that were assigned to SrF2 and NaYbF4. A negligible amount of Yb3+ ions that were converted into Yb2+ ions was also detected with XPS. From the photoluminescence data it was evident that the Na+ ions induced noticeable change to the NIR emission. This might reduce the quantum efficiency between the Pr3+ and Yb3+ ions in the system.
