Abstract
The optical properties of SrSi 2O 2N 2 doped with divalent Eu 2+ and Yb 2+ are investigated. The Eu 2+ doped material shows efficient green emission peaking at around 540 nm that is consistent with 4f 7→4f 65d transitions of Eu 2+. Due to the high quantum yield (90%) and high quenching temperature (>500 K) of luminescence, SrSi 2O 2N 2:Eu 2+ is a promising material for application in phosphor conversion LEDs. The Yb 2+ luminescence is markedly different from Eu 2+ 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 Eu 2+ and Yb 2+ relative to the valence and conduction bands of the oxonitridosilicate host material.
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