Near-UV-Excitable Sm3+/Eu3+-Activated Na3YB8O15 Red Phosphors with High Thermal Stability for LED Applications

Near-ultraviolet-excitable red phosphors with high thermal stability are desirable for phosphor-converted LED applications, including potential plant-lighting applications. Herein, Sm3+- and Eu3+-activated Na3YB8O15 phosphors were synthesized by a high-temperature solid-state reaction. Among the investigated compositions, the optimal activator contents were identified as x = 0.02 for Na3YB8O15:xSm3+ and y = 0.70 for Na3YB8O15:yEu3+, with concentration quenching in both series mainly governed by dipole–dipole interactions. In the Sm3+/Eu3+ co-doped phosphors, the emission color shifted from orange-red toward red as the Eu3+ content increased. At 433 K, the Sm3+-doped, Eu3+-doped, and Sm3+/Eu3+ co-doped samples retained 119.7%, 93.4%, and 102.3% of their room-temperature integrated emission intensities, respectively. The high thermal stability may be attributed to the structural characteristics of the host, its wide optical band gap, and the temperature-dependent redistribution of Stark and phonon-assisted emission components. A phosphor-converted LED fabricated using Na3YB8O15:0.02Sm3+,0.01Eu3+ and a commercial 400–405 nm, 5 W near-UV LED chip produced multiband emission that partially overlapped with the absorption bands of both chlorophylls and the PR and PFR forms of phytochrome. These results suggest that Sm3+/Eu3+-activated Na3YB8O15 is a promising thermally robust, spectrum-adjustable red phosphor for LED applications.