Relationship between Eu3+ substitution sites and photoluminescence properties of SrIn2O4:Eu3+ spinel phosphors

Eu3+-doped SrIn2O4 phosphors were synthesized by the solid solution method at 1400 °C in air. The chemical composition of the phosphors was systematically changed to study the relation between the Eu3+ substitution site and photoluminescence (PL) properties. Under excitation of the 7F0→5L6 transition of Eu3+ at 393 nm, the SrIn2O4:Eu3+ exhibited dominant red emission peaks at 611, 616 and 623 nm, which are attributed to the electric dipole transition 5D0→7F2 of Eu3+. The results of X-ray diffraction analysis combined with PL spectroscopic analysis revealed that Eu3+ ions occupied two different crystallographic In3+ sites in the host SrIn2O4, while it was found to be impossible to substitute Sr2+ with Eu3+ prior to the Eu3+ substitution at the In3+ sites in the SrIn2O4. The intensity of the red emission peaks increased with the total amount of dopant Eu3+ ion at the two In3+ sites, and reached a maximum at 25 mol% Eu3+-doping (SrIn2−xO4:xEu3+, x=0.25). Moreover, a small amount (<10 mol%) of Eu3+ at the Sr2+ site in the SrIn2−xO4:xEu3+ was found to contribute to enhance the red emission peak intensity at 616 nm. As a result, the highest red emission intensity evaluated as the total emission peak intensities at the 611, 616 and 623 nm was achieved for Sr0.92In1.75O4:0.33Eu3+ in which Eu3+ ion concentrations at the In3+ and Sr2+ sites were simultaneously optimized as 25 and 8 mol%, respectively (Sr1−yIn2−xO4:(x+y)Eu3+, x=0.25, y=0.08). This red emission intensity was 2.2 times higher than that of the phosphor without contribution of the Eu3+ at the Sr2+ site (SrIn2−xO4:xEu3+, x=0.25). The critical energy transfer distance of Eu3+ ion in the Sr0.92In1.75O4:0.33Eu3+ phosphor was determined to be 0.817 nm, and the electric multipolar interaction was suggested as the dominant mechanism for concentration quenching of PL emission due to Eu3+ ions in the Eu3+-doped SrIn2O4 phosphors investigated in this study.