Enhancement of SrSi₂O₂N₂:Eu²⁺ phosphor by means of oxygen to nitrogen control

In this study phosphor powders with the nominal composition of Sr_0.98Eu_0.02Si₂O_(5–1.5x)N_x (x in the range of 1.33–2.66) was successfully synthesized through the conventional solid-state reaction method. We carried out studies on the N^3- and O^2- ions effects on the structural and photoluminescent properties of the resultant oxonitridosilicates by varying nitrogen content in the initial mixture of materials. Discussion on the multicomposition effect on the luminescent properties is provided since the specimen with the bi-phase composition shows the highest quantum yield (QY) among the examined specimens. We found that luminescence peaked at 540 nm is related to Eu²⁺ located in the triclinic phase SrSi₂O₂N₂. It is shown that QY of the single triclinic phase materials is relatively low. We related low QY to absorption of excitation light by uncontrolled defects. We found that the sample where the ratio of Si in silica to Si in silicon nitride is 0.5:1.5 has high QY equal to 0.68. This sample is a mixture of two phases: the triclinic phase SrSi₂O₂N₂ and another crystal lattice, the most likely Sr₃Si₆O₉N₄. We can relate the parasite defects to the surface states in the triclinic lattice, which in the case of existence, the Sr₃Si₆O₉N₄ phase are removed.