Influence of Flux on Morphology and Luminescence Properties of Phosphors: A Case Study on Y1.55Ti2O7:0.45Eu3+

A series of Y1.55Ti2O7:0.45Eu(3+) phosphors with orange-red emission under near ultraviolet excitation were prepared in solid-state reaction with NH4Cl, NH4F, H3BO3, LiF, and NaF as flux, respectively. Comparative studies showed that flux could not only modify the morphology and grain size, but have a significant influence on the spatial distribution of Eu3+ activator across the Y2Ti2O7 host. NaF flux, the best one among the five flux materials, helped the phosphor particles to have a sphere-like morphology, micrometer-level grain size as well as uniform spatial distribution of activator, and enhanced the photoluminescence of Y1.55Ti2O7:0.45Eu(3+)+ phosphor by a factor of about 16 at an optimal amount. Other fluxes also exhibited positive effect on photoluminescence of the phosphor in a sequence of NH4Cl < NH4F < H3BO3 < LiF, and influenced the morphology, grain size, activator spatial distribution of the phosphor particles in varied extents. The influence of these flux materials on phosphor grain growth was discussed by the Ostwald ripening mechanism, with consideration of the melting point, boiling point (or decomposition temperature), as well as reactivity of the flux materials. In addition, the influence of flux on photoluminescence intensity and lifetime of Y1.55Ti2O7:0.45Eu(3+) was also discussed.