Realizing efficient Mn2+ red emission via synergistic sensitization of Eu2+ and Tb3+ for white light-emitting diodes

Abstract

Mn2+-activated red-emitting phosphors have emerged as promising candidates for phosphor-converted white light-emitting diodes (WLED). Unfortunately, optical center Mn2+ suffers from weak emission and inefficient excitation due to its forbidden d-d transition. Often, a sensitizer (e.g., Eu2+/Ce3+ or Tb3+) is required to pair with Mn2+ (mono-sensitization strategy) to enhance emission/excitation efficiency of Mn2+ (e.g., Eu2+/Ce3+/Tb3+→Mn2+), with the energy transfer (ET) principle. However, at present, sufficiently sensitizing Mn2+ by using the above strategy to yield a nearly pure, efficient Mn2+ red emission still remains challenging. Herein, we demonstrate a sufficient sensitization of Mn2+ in Sr3La3(PO4)3 compounds by utilizing two sensitizer ions, Eu2+ and Tb3+, to synergistically sensitize one Mn2+, which brings out a new, high-efficient Eu2+→Tb3+→Mn2+ ET, achieving almost pure, bright Mn2+ red emission without seeing the emissions from Eu2+ and Tb3+ in a composition-optimized sample. The intensity of the resulting Mn2+ red emission is better than that of each mono-sensitization strategy. Moreover, a high-quality WLED with high color-rendering-indexing of 91 and low correlated color temperature of 4436 K is achieved by using as-prepared red-emitting phosphor. We believe that such a strategy can be easily expanded to other systems, initiating a new pathway in designing the Mn2+-activated red phosphors.