Energy transfer processes leading to strong NIR-to-red upconversion in the Yb-concentrated Sr3Yb0.98Er0.02(PO4)3 eulytite

The optical spectroscopy and the decay kinetics of samples with composition Sr3Yb(PO4)3, Sr3Y0.98Yb0.02(PO4)3, Sr3Y0.98Er0.02(PO4)3 and Sr3Yb0.98Er0.02(PO4)3 have been studied at room temperature. The presence of efficient energy transfer and migration processes has been clearly evidenced in the Sr3Yb(PO4)3 and Sr3Yb0.98Er0.02(PO4)3 materials, giving rise to strong visible upconversion upon excitation in the spectral region around 1 μm in the latter material. The strong anti-Stokes emission is connected to fast migration in the 2 F5/2 level of Yb3+, due to the inefficient concentration quenching for this ion. In this class of materials, the upconversion processes could be optimized even in the presence of high concentrations of the Yb3+ sensitizer.