Synthesis and optical properties of highly efficient red-emitting K2LaNb5O15:Eu3+ phosphors

Polycrystalline powders of K2LaNb5O15 doped with Eu3+ ions were prepared by high temperature solid state reaction. The phase formation of these compounds was monitored by X-ray diffraction measurements. Excitation of the prepared phosphors with near-UV or blue radiation resulted in a bright red luminescence, dominated by 5D0 → 7F2 transition at ca. 613 nm, with excellent colour saturation. The colour coordinates were relatively stable regardless the Eu3+ concentration and temperature. Furthermore, sample doped with 75% Eu3+ showed high 66% quantum efficiency if excited at 394 nm. Temperature dependent photoluminescence and decay measurements showed that internal quantum efficiency of the phosphors decreases slower than the external quantum efficiency at elevated temperatures. Moreover, synthesized K2LaNb5O15:Eu3+ phosphors possess rather unique emission spectra with strong and finely split emission lines originating from the 5D0 → 7F4 transition (ca. 700 nm) what makes these materials very attractive for application in luminescent security pigments.