Highly efficient and thermally stable single-activator white-emitting phosphor K2Ca(PO4)F:Eu2+ for white light-emitting diodes

Abstract

Phosphor-converted white light-emitting diodes (w-LEDs) have become the new generation of lighting. Several strategies have been introduced to realize a high CRI value for illumination. However, these strategies suffer from new problem(s), such as reabsorption, different deterioration rates among the phosphors, different thermal stability for diverse emission bands, and/or the decrease of quantum efficiency for the phosphor. Therefore, it is desired to develop new phosphors that not only realize a high CRI value for w-LEDs, but also resolve the above problems. In this work, a site-preference driven color-tunable Eu²⁺-activated K₂Ca(PO₄)F phosphor was prepared. The color-tunable phosphor exhibits two broad emission bands peaking at 485 and 660 nm upon UV excitation. White emission is realized in K₂Ca(PO₄)F:0.006Eu²⁺. The internal and external quantum efficiencies of the white-emitting phosphor are 91.5 and 66.9%, respectively. The phosphor also exhibits good thermal stability, namely, the emission intensity at 423 K maintains >80% of that at room temperature, and the intensity ratio between the two emission bands remains nearly unchanged within 423 K. A white LED device has also been fabricated using a 365 nm LED chip and K₂Ca(PO₄)F:0.006Eu²⁺, showing a high color rendering index (R_a = 87.6). These results indicate that the K₂Ca(PO₄)F:Eu²⁺ phosphor is a promising candidate for UV-pumped w-LEDs.