Behavior of Eu ions in SrSnO3: Optical properties, XPS experiments and DFT calculations

This study reports the synthesis and characterization of SrSnO3:Eu phosphors with various doping concentrations synthesized via a modified sol-gel method. The samples were characterized by powder X-ray diffraction (PXRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. PXRD and Raman spectroscopy showed that the samples crystallized with the orthorhombic perovskite crystal structure, which density functional theory (DFT) calculations suggest is the most energetically stable modification. In addition, Rietveld refinements and XPS analysis indicate that the Eu3+ ion replaces Sr2+ (noncentrosymmetric site) for samples with 1% and 3% Eu3+, while at higher concentrations of dopant, the Eu3+ ions replace both Sr2+ and Sn4+ (centrosymmetric site). Photoluminescence measurements show the characteristic emission spectra of Eu3+, in which the ratio of the intensities of the red/orange PL peaks is a maximum at 3% Eu3+ and then decreases continuously with concentration. This supports the conclusion that Eu3+ ions replace Sr2+ at low concentrations, but Sr2+ and Sn4+ at higher concentrations.