Luminescence of Eu³⁺ and Sm³⁺ Doped Potassium Tungstate Phosphor

The luminescent properties of Eu³⁺ and Sm³⁺ doped potassium tungstate phosphor are investigated. The K_4–3x (WO₄)₂ : Eu³⁺ _x, Sm³⁺ _y phosphor is produced by firing the mixed precursors, followed by re-firing with a flux. The re-firing process results in the defect-free surface and uniform growth of the particles. The strong absorption in the region of ultra violet light is observed due to the 4f-4f electron transitions of the Eu³⁺ and Sm³⁺ ions. The doping concentration of europium into potassium tungstate is relatively high, compared to other host materials. It is revealed that the crystal structure is a monoclinic with space group, C2/c. This crystal structure facilitated the Eu3+ ions to be located with the Eu-Eu distance larger than 5 Å so that concentration quenching does not occur even at high doping concentration. The excitation spectrum could be adjusted by the introduction of the samarium. A small amount of the Sm3+ ions that acts as a sensitizer increases the energy absorption peak around 405 nm.