A new strategy to improve the thermal stability of (Sr, Ba)2SiO4: Eu2+ phosphors by ion substitution engineering

With high quantum efficiency and appropriate excitation & emission wavelength, (Sr, Ba)2SiO4: Eu2+ phosphors exhibit perfect photoluminescence properties in the room temperature. However, limited by its poor thermal stability, they are difficult to be applicated in the high-performance lighting and display fields. In this work, we propose a new strategy of ion substitution engineering to greatly improve the thermal stability of (Sr, Ba)2SiO4: Eu2+ phosphors. Through the conventional high-temperature solid-state reaction, we successfully introduced alkali metal ions K+/Na + into the SrBaSiO4 host lattice, thereby strengthening its structural rigidity, and improving the luminous intensity and narrowing the Full-Width Half-Maximum (FWHM) of the phosphors. The substitution of K+/Na+ ions can also deepen the traps in the phosphor, which proved by the thermoluminescence (TL) measurement. Joint effect of the stronger crystal rigidity and deeper traps leads to a higher thermal stability, and the emission intensity at 150 °C can reach to 81.5% of that at room temperature with Na+ substitution, which is significantly better than the commercial SrBaSiO4: Eu2+ phosphor. The mechanism of alkali metal ions improving thermal stability is explained reasonably through the photoionization and trap compensation. This new strategy makes it possible for (Sr, Ba)2SiO4: Eu2+ phosphors to be wider applicated in the high-performance WLED devices.