Phosphor-converted light-emitting diodes (pc-LEDs) represent a key technology in solid-state lighting. However, their performance and reliability are often limited by the thermal instability of conventional phosphors under high-power operation. To address this challenge, this study reports two thermally stable red-emitting phosphors, NaYMgWO6:Sm3+ and NaYMgWO6:Eu3+, synthesized via a high-temperature solid-state reaction method. A remarkable abnormal thermal quenching behavior is observed in NaY0.97MgWO6:0.03Sm3+, whose luminescence intensity at 348 K exceeds the room-temperature value. Meanwhile, NaY0.7MgWO6:0.3Eu3+ exhibits outstanding thermal stability, retaining 80.82% of its room-temperature emission intensity at 423 K. Under near-UV and blue excitation, NaYMgWO6:Sm3+ and NaYMgWO6:Eu3+ emit intense orange-red (645 nm) and red (615 nm) light with high color purity values of 85.81% and 96.58%, respectively, and show negligible chromaticity drift up to 448 K. Notably, the internal quantum efficiency reaches 27.59% for the Sm3+-doped phosphor and 88.86% for the Eu3+-doped counterpart. Practical application is demonstrated through fabricated pc-LED prototypes, which produce bright orange-red and red emissions. Furthermore, when incorporated into white LED devices along with a commercial yellow phosphor and a blue chip, the developed red phosphors effectively compensate for the spectral deficiency in the red region, significantly improving the color rendering performance and yielding warm white light with a high color quality. These results highlight the promising potential of the developed NaYMgWO6:Sm3+/Eu3+ phosphors for high-stability solid-state lighting applications.
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