A novel red-emitting phosphor K2MgGeO4:Eu3+ for WLEDs: zero-thermal quenching induced by heterovalent substitution

Abstract

The popularity of high-power LEDs drives mounting demands for thermal stability of luminescent materials, of which the satisfactory performance via subjective structural design is still a great challenge. Herein, we propose an effective defect-modulated strategy to fulfill the excellent performances of red-emitting phosphors K₂MgGeO₄:Eu³⁺, including high quantum efficiency (94.98%) and zero-thermal quenching. The distribution of lattice defects was studied in detail through experimental investigations and first principles calculations. It is demonstrated that the heterovalent substitution process (Eu³⁺–K⁺) creates quantitative potassium vacancies, and interstitial oxygen atoms are also observed in the host. Those defects form trap levels, and most of them are in the deep position of the forbidden band (E = 1.30 eV). Under the stimulus of thermal activation, the electrons detrapped from the defect levels return to the luminescent center to realize radiative recombination and compensate for the energy loss caused by non-radiative transition at high temperatures. Correspondingly, a defect-assisted model was constructed to depict the whole photoluminescence process. Finally, a fabricated WLED with a good color rendering index (R_a = 91.7) manifests the prominent application potential of the as-prepared sample. This study not only deepens the understanding of the response mechanism between optical properties and defects, but also broadens the channel to explore novel functional materials with good thermal stability.