Effect of local environment and Sm³⁺-codoping on the luminescence properties in the Eu³⁺-doped potassium tungstate phosphor for white LEDS

The luminescence properties of Eu³⁺- and Sm³⁺-doped potassium tungstate phosphors were investigated. The K_4-3(x+y) (WO₄)₂:Eu_x³⁺,Sm_y³⁺ phosphor was produced by solid-state reactions, followed by re-firing with a flux. The phosphor showed a strong absorption in the near-UV to green region due to 4f-4f electron transitions of the Eu³⁺ and Sm³⁺ ions, generating a red emission. The excitation spectrum could be adjusted by Sm³⁺-codoping. A small amount of Sm³⁺, acting as a sensitizer, increased the energy absorption peak at 405 nm. The crystal structure and local environment around the Eu³⁺ ions were determined using the Rietveld method. The crystal structure of this phosphor was determined to be monoclinic with a space group of C2/c. The small Eu-0 distance in the crystal led to high energy-level splitting at the ⁵D₀→⁷F₂ transition of the Eu³⁺ ions, resulting in more emission peaks. Crown