A competitive trivalent-europium-activated phosphor: Achieving highly efficient red light emission in a sodium-rich garnet host

The reaction temperature is key factor for light-emitting phosphors synthesized by solid state method because it directly determines the crystallinity and further affects the luminescence property of the phosphors. While high temperature certainly benefits to the solid diffusion in reaction, it would waste enormous energy during long time heating. Herein, a novel Eu3+-activated and highly efficient red phosphor, NaGd2Ga3Ge2O12:Eu3+, is reported. By the reconstruction of the traditional Y3Al5O12 garnet host into the sodium-rich NaGd2Ga3Ge2O12 one, huge decrease of the synthesis temperature is successfully achieved. More importantly, such decrease of the synthesis temperature does not dissatisfy the luminescence property of the NaGd2Ga3Ge2O12:Eu3+ phosphors. Instead, the Eu3+ in the NaGd2Ga3Ge2O12 exhibits extremely high quantum yield up to 96.78% upon 394 nm excitation, showing great competitiveness among other iso-structral garnet hosts. This work indicates that the introduction of sodium in the eight-coordinated rare earth site of the garnet host can not only reduce the energy consumption during the stage of phosphor synthesis but also avoid the loss of excitation energy during the light converting stage of the Eu3+ to a large extent. By fabricating the as-synthesized red phosphor into a near-UV chip together with commercial green and blue phosphors, quality white light-emitting diodes with satisfactory color rendering index (as high as 90) and correlated color temperature (as low as 3986 K) can be easily obtained.