Tunable luminescence and energy transfer properties of KSr4(BO3)3:Dy3+, Eu3+ phosphors for near-UV warm-white LEDs

Dy3+ and Eu3+ codoped KSr4(BO3)3 phosphors were successfully synthesized by solid-state reaction process. Under near-ultraviolet (near-UV) excitation, individual Dy3+ or Eu3+ ion activated sample exhibits characteristic emissions in their respective regions. In KSr4(BO3)3:Dy3+, xEu3+ phosphors, the energy transfer from Dy3+ to Eu3+ was revealed to be resonant type by dipole–dipole mechanism. And the critical distance RDy–Eu was calculated to be 13.95 Å. The energy transfer efficiency of KSr4(BO3)3:Dy3+, xEu3+ reached about 20% when the concentration of Eu3+ was 0.035. Moreover, the emitting colors of Dy3+ and Eu3+ codoped samples can be adjusted from the edge of white area to warm white via tuning the activator (Eu3+) doped concentration. More significantly, the chromaticity coordinates (0.334, 0.351) of KSr4(BO3)3:0.005Dy3+, 0.015Eu3+ sample are extremely adjacent to standard white light (0.33, 0.33). The quantum efficiency of the KSr4(BO3)3:0.005Dy3+, 0.015Eu3+ phosphor with 389 nm excitation is found to be 42%, demonstrating that the obtained single-component white-emitting phosphor exhibits potential applications for solid state lighting.