Synthesis and optical properties of efficient orange emitting GdB₅O₉:Sm³⁺ phosphors

In the present study the single phase polycrystalline GdB₅O₉:Sm³⁺ target materials were prepared by aqueous sol–gel method. The powder X-ray diffraction was used to monitor the crystal phase formation. Samples doped with 1 and 2.5% Sm³⁺ showed bright orange–red emission upon excitation with near-UV radiation. The emission possessed excellent colour saturation and good colour coordinate stability. Emission spectra recorded at different temperatures showed that the thermal quenching activation energy is around 35 meV. Moreover, the temperature dependent photoluminescence (PL) decay measurements revealed that PL lifetime values barely change in the temperature range of 77–500 K showing that the external quantum yield decreases much faster than the internal one. The highest quantum yield of ca. 60% was obtained for the sample doped with 1% Sm³⁺ ions. Further increase of Sm³⁺ content resulted in concentration quenching as a consequence of increased probability of cross-relaxation. Rather high quantum yield and well resolved sharp emission lines makes these phosphors suitable for application as an orange–red component in near-UV LEDs, on the one hand, and the luminescent security pigments, on the other hand.