Dipole – dipole and dipole – quadrupole interactions between Sm³⁺ ions in K₄BaSi₃O₉

K₄BaSi₃O₉ (KBSO) doped with Sm³⁺ was synthesized for the first time by conventional solid-state method. Results of XRD measurements confirm that the obtained powder is K₄BaSi₃O₉ single phase. The new material exhibits red luminescence with maximum at 641 nm under 407 nm excitation. At 300 K the luminescence intensity is quenched for Sm³⁺ concentration above 0.5%. The decay profiles revealed the non-radiative energy transfer between the Sm³⁺ ions. The interaction has dipole – dipole character for low Sm³⁺ concentrations (up to 1%) then dipole – quadrupole for higher dopant concentration (over 1%). The critical distances are 8.8 Å and 9.5 Å for dipole – dipole and the latter interactions, respectively. This phenomenon is explained by analyzing the probability of occupation of all possible sites available for Sm³⁺ in KBSO taking into account local charge compensation. The site occupation preference by Sm³⁺ ions depends on the distances between available cation sites.