Luminescence properties of SrSi2O2N2 doped with divalent rare earth ions

The optical properties of SrSi2O2N2 doped with divalent Eu2+ and Yb2+ are investigated. The Eu2+ doped material shows efficient green emission peaking at around 540 nm that is consistent with 4f7→4f65d transitions of Eu2+. Due to the high quantum yield (90%) and high quenching temperature (>500 K) of luminescence, SrSi2O2N2:Eu2+ is a promising material for application in phosphor conversion LEDs. The Yb2+ luminescence is markedly different from Eu2+ and is characterized by a larger Stokes shift and a lower quenching temperature. The anomalous luminescence properties are ascribed to impurity trapped exciton emission. Based on temperature and time dependent luminescence measurements, a schematic energy level diagram is derived for both Eu2+ and Yb2+ relative to the valence and conduction bands of the oxonitridosilicate host material.