Site occupancy preference of Bi3+ and Bi3+–Eu3+ codoped yttrium galliate phosphors for white LEDs

Abstract

A variety of Bi³⁺-activated and Bi³⁺–Eu³⁺ codoped Y₃GaO₆ phosphor samples were obtained by solid-state reaction. The phase purity and crystal structure of the specimens were characterized via powder X-ray diffraction (XRD) analysis and Rietveld refinement. For the single Bi³⁺-doped Y₃GaO₆ phosphor, two different PL peaks at 410 and 595 nm were obtained, resulting from the two different Bi³⁺ sites occupied. The site occupation is driven by Bi³⁺ ion concentration. There is an energy transfer from the Bi³⁺ to Eu³⁺ ions in the YGO:Bi³⁺,Eu³⁺ phosphors. Besides, the energy transfer mechanism, efficiencies, quantum efficiency and thermal stability have been discussed in detail, demonstrating that the sample possesses high quantum efficiency and good thermal stability. The high color-rendering index R_a (92.9, and 81.6) and low CCT (3286 K, and 3904 K) of the white light-emitting diodes (WLEDs) clearly indicate that these samples are promising candidates for WLEDs.