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 K4−3(x+y) (WO4)2:Eux3+,Smy3+ 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.