Color-tunable emission in Ca₃Lu₂Ge₃O₁₂: Bi³⁺, Eu³⁺ phosphor through energy transfer for WLEDs

To achieve white light-emitting diodes (WLEDs) with an extensive color gamut, developing phosphors with narrow-band and color-tunable emitting is in great demand in current research. In our work, a straightforward solid-state process was used to create the cyan to orange-red color-tunable phosphor of Ca₃Lu₂Ge₃O₁₂: Bi³⁺, Eu³⁺ (CLGO: Bi³⁺, Eu³⁺). The broad and strong photoluminescence excitation (PLE) band of CLGO: Bi³⁺, Eu³⁺ in the range of 250–450 nm deriving from the superposition of the Bi³⁺ and Eu³⁺ excitations, implying CLGO: Bi³⁺, Eu³⁺ viable for both ultraviolet (UV) and near ultraviolet (NUV) LED chips. By tuning the doing concentrations of Bi³⁺/Eu³⁺ ions, the luminous color of CLGO: Bi³⁺, Eu³⁺ can be finely tuned across an ultra-wide range, transitioning from cyan (Bi³⁺) to cold white, and ultimately to the orange-red region (Eu³⁺). The energy transfer (ET) process has been proven to relate to dipole-dipole interaction, and an efficiency of 53.98 % is achieved. In addition, the CLGO: Bi³⁺, Eu³⁺ phosphor shows good thermal stability. The luminous intensities of Bi³⁺ and Eu³⁺ in the CLGO: 4%Bi³⁺, 8%Eu³⁺ sample (λ_ex = 360 nm) are 62.19 % and 46.3 % (at 423 K) of their respective values. The temperature-controlled PL spectrum exhibited a slight chromaticity shift (Δs = 1.03 × 10⁻² for 303–473 K). The internal quantum efficiency (IQE) value of CLGO: 4%Bi³⁺, 8%Eu³⁺ could reach 59.21 % at the excitation of 360 nm. Thus, the color-tunable CLGO: Bi³⁺, Eu³⁺ phosphor can be applied as a single-component white light phosphor or monochromatic component in WLEDs.