A novel white Y₂(Ti_0.8Hf_0.2)₂O₇: Eu phosphors regulated by HfO₂ exhibiting low color shifting for high temperature

The development of white phosphors that can be activated in near-ultraviolet light is highly important in the field of LED lighting. In this work, a series of color-tunable Y₂(Ti_1-xHf_x)₂O₇:Eu phosphors were prepared by adjusting the HfO₂ and Eu³⁺ concentrations. In particular, white Y₂(Ti_0.8Hf_0.2)₂O₇:Eu phosphors were successfully synthesized and emitted a broad band covering the entire visible light region upon excitation with 340 nm UV light. The white banded materials were composed of Eu²⁺ and Eu³⁺ emissions and HfO₂ defect emission. The formation of Eu²⁺ ions was caused by the introduction of HfO_2, which causes self-reduction of Eu³⁺ ions but does not require additional reducing agents. The white Y₂(Ti_0.8Hf_0.2)₂O₇:Eu phosphors exhibit low color shifting at high temperature, which is very important for LED applications. The chromaticity shift of the Y₂(Ti_0.8Hf_0.2)₂O₇:0.2Eu phosphor is 2.83 × 10^-2 at 503 K, which is only 54.8 % that of commercial three-color white phosphors at the same temperature. The Ra value did not decrease significantly with increasing temperature and reached 90.2 at 383 K. Y₂ (Ti_0.8Hf_0.2)₂O₇:0.2Eu phosphors were assembled with a 365 nm LED chip to fabricate a WLED device that showed excellent white-colored coordinates (0.345, 0.358) and a high Ra value of 90.1 under a 300 mA current.