Blue-light-pumped wide-band red emission in a new Ce³⁺-activated oxide phosphor, BaCa₂Y₆O₁₂:Ce³⁺: Melt synthesis and photoluminescence study based on crystallographic analyses

Based on a proposed new materials design concept, we succeeded in discovering a new red-emitting oxide phosphor, BaCa₂Y₆O₁₂:Ce³⁺, via a melt synthesis technique using an arc-imaging furnace. Rietveld refinement using X-ray diffraction data gave the crystal structure of the obtained phosphor, which has the same framework as the reported host lattice, hexagonal BaCa₂Y₆O₁₂. However, the structure between the Ba and Ca atoms was partially disordered, and the site symmetry for the Ba site decreased from the 2a and 2b Wyckoff positions to 4e. The phosphor shows a reddish-yellow colour emission with a broad-band spectrum under blue-light irradiation at 460 nm. The emission spectrum was composed of four Gaussian bands, indicating Ce³⁺ is incorporated into two different sites, Ca²⁺-dominant and Y³⁺ sites, and this could be estimated using an empirical equation for determining the emission wavelength from crystallographic data and chemical compositions. Additionally, based on the observation of the particle morphology, the measurement of Ce³⁺ concentration and the thermal dependence of the luminescence intensity and luminescence lifetime property, BaCa₂Y₆O₁₂:Ce³⁺ has high potential as a fundamental material. Crystal-field analysis based on the refinement of the crystal structure revealed the luminescence mechanism. The present work includes unique results on a distinct material design concept for a red-emitting oxide phosphor, which should have great significance for future phosphor material development.