Concentration-Driven Selectivity of Energy Transfer Channels and Color Tunability in Ba<sub>3</sub>La(PO<sub>4</sub>)<sub>3</sub>:Tb<sup>3+</sup>, Sm<sup>3+</sup> for Warm White LEDs

Here, we report the large-scale emission color tunability in Ba<sub>3</sub>La­(PO<sub>4</sub>)<sub>3</sub>:Tb<sup>3+</sup>, Sm<sup>3+</sup> (BLPO:TS) system based on the detailed discussion on the concentration-driven selectivity of energy transfer (ET) channels from Tb<sup>3+</sup> to Sm<sup>3+</sup>. It is induced by the concentration-dependent <sup>5</sup>D<sub>3</sub> and <sup>5</sup>D<sub>4</sub> emissions of Tb<sup>3+</sup> and the different interaction mechanisms of ET from Tb<sup>3+</sup> to Sm<sup>3+</sup> via <sup>5</sup>D<sub>3</sub> and <sup>5</sup>D<sub>4</sub> channels. In the diluted Tb<sup>3+</sup> scenario, the red emission of Sm<sup>3+</sup> is efficiently sensitized via the <sup>5</sup>D<sub>3</sub> channel, while in the concentrated Tb<sup>3+</sup> case, the contribution of <sup>5</sup>D<sub>4</sub> channel is dominant. Therefore, by simply adjusting the doping concentrations of Tb<sup>3+</sup> and Sm<sup>3+</sup>, the emission color of the phosphors can be tuned from green to red. In view of the phosphors with red emissions are critical to the warm white light-emitting diodes (WLEDs), an orange-red Tb<sup>3+</sup>, Sm<sup>3+</sup> coactivated phosphor Ba<sub>3</sub>La<sub>0.90</sub>Tb<sub>0.05</sub>Sm<sub>0.05</sub>(PO<sub>4</sub>)<sub>3</sub> (BLPO:5T5S) with good thermal and chromaticity stability and internal quantum efficiency ∼67% is developed in the system. Then, a near-UV WLED (CCT ≈ 4500 K, <i>R</i><sub>a</sub> ≈ 81) is fabricated using this phosphor. These findings not only indicate that the orange-red phosphor BLPO:5T5S is available for near-UV warm white LEDs but also deliver new insights into the ET processes in Tb<sup>3+</sup> and Sm<sup>3+</sup> activated phosphors.